45 MCP Tools: Everything Your Claude Agent Can Do with a Wallet

Ever tried asking Claude to check your crypto balance or swap tokens? You probably got a polite “I can’t access external wallets” response. That changes today.

WAIaaS is an MCP server that gives Claude Desktop a complete wallet toolkit. Add one configuration block, and your AI assistant can check balances, send transactions, execute DeFi strategies, and manage NFTs — all through natural conversation.

Why MCP + Wallets Matter

Claude’s Model Context Protocol (MCP) lets you extend the AI with custom tools. But most MCP servers focus on file systems, databases, or APIs. WAIaaS fills the blockchain gap.

Instead of switching between Claude for analysis and MetaMask for execution, you get both in one interface. Ask Claude to “check my DeFi positions and rebalance if necessary” — and it can actually do it.

The stakes are real money, so WAIaaS includes production-grade security: policy engines, approval workflows, and default-deny enforcement. Your agent gets superpowers, but you stay in control.

45 MCP Tools in One Package

WAIaaS provides 45 MCP tools across five categories:

Wallet Management (8 tools)

  • get-balance — Native token balance
  • get-assets — All token balances with prices
  • get-address — Wallet address and chain info
  • get-wallet-info — Complete wallet overview
  • list-nfts — NFT collection with metadata
  • get-nft-metadata — Individual NFT details
  • get-health-factor — DeFi health across protocols
  • resolve-asset — Token info by symbol/address

Transaction Operations (11 tools)

  • send-token — Native and token transfers
  • transfer-nft — NFT transfers with metadata
  • send-batch — Multiple transactions atomically
  • approve-token — Token spending approvals
  • call-contract — Arbitrary contract calls
  • sign-transaction — Raw transaction signing
  • sign-message — Message signing for auth
  • simulate-transaction — Dry-run before execution
  • get-transaction — Transaction details by ID
  • list-transactions — Transaction history
  • get-nonce — Account nonce for advanced usage

DeFi Integration (8 tools)

  • get-defi-positions — All lending/staking positions
  • action-provider — Execute DeFi actions
  • hyperliquid — Perpetual futures trading
  • polymarket — Prediction market trades
  • get-provider-status — DeFi protocol health
  • list-offchain-actions — Available DeFi operations
  • encode-calldata — Generate transaction data
  • x402-fetch — HTTP requests with automatic payment

Here’s Claude executing a Jupiter swap on Solana:

# Behind the scenes when Claude calls action-provider
curl -X POST http://127.0.0.1:3100/v1/actions/jupiter-swap/swap 
  -H "Content-Type: application/json" 
  -H "Authorization: Bearer wai_sess_<token>" 
  -d '{
    "inputMint": "So11111111111111111111111111111111111111112",
    "outputMint": "EPjFWdd5AufqSSqeM2qN1xzybapC8G4wEGGkZwyTDt1v",
    "amount": "100000000"
  }'

Advanced Features (10 tools)

  • build-userop — ERC-4337 Account Abstraction
  • sign-userop — Gasless transaction signing
  • erc8004-get-agent-info — Onchain agent reputation
  • erc8004-get-reputation — Trust scoring
  • erc8004-get-validation-status — Agent validation
  • erc8128-sign-request — HTTP request signing
  • erc8128-verify-signature — Signature verification
  • wc-connect — WalletConnect pairing
  • wc-disconnect — WalletConnect termination
  • wc-status — Connection status

System Management (8 tools)

  • get-policies — Security policy overview
  • list-sessions — Active agent sessions
  • list-credentials — Stored credentials
  • connect-info — Network and RPC status
  • get-rpc-proxy-url — Blockchain RPC access
  • list-incoming-transactions — Deposit monitoring
  • get-incoming-summary — Deposit analytics
  • get-tokens — Supported token list

Quick Setup: 5 Minutes to AI Wallet

Step 1: Install WAIaaS

npm install -g @waiaas/cli
waiaas init
waiaas start

Step 2: Create a wallet and session

waiaas quickset --mode mainnet

This creates wallets for both Ethereum and Solana, plus MCP sessions for each. You’ll see output like:

Created wallet: ethereum-mainnet (0x742d35Cc...)
Created wallet: solana-mainnet (5Fz9k2bN...)
Created session: wai_sess_eyJhbGciOiJIUzI1NiJ9...

Step 3: Configure Claude Desktop

Add this to ~/Library/Application Support/Claude/claude_desktop_config.json:

{
  "mcpServers": {
    "waiaas": {
      "command": "npx",
      "args": ["-y", "@waiaas/mcp"],
      "env": {
        "WAIAAS_BASE_URL": "http://127.0.0.1:3100",
        "WAIAAS_SESSION_TOKEN": "wai_sess_eyJhbGciOiJIUzI1NiJ9...",
        "WAIAAS_DATA_DIR": "~/.waiaas"
      }
    }
  }
}

Or use the auto-setup command:

waiaas mcp setup --all

Step 4: Restart Claude Desktop

Claude will now see 45 new tools. The MCP connection indicator shows “waiaas” as connected.

Step 5: Try it out

Open a new Claude conversation and ask:

  • “Check my wallet balance”
  • “What tokens do I own?”
  • “Show my DeFi positions”
  • “Swap 0.1 SOL for USDC on Jupiter”

Multi-Wallet Configuration

For production agents, configure separate MCP servers per wallet:

{
  "mcpServers": {
    "waiaas-trading": {
      "command": "npx", 
      "args": ["-y", "@waiaas/mcp"],
      "env": {
        "WAIAAS_BASE_URL": "http://127.0.0.1:3100",
        "WAIAAS_AGENT_ID": "019c47d6-51ef-7f43-a76b-d50e875d95f4",
        "WAIAAS_AGENT_NAME": "trading-agent"
      }
    },
    "waiaas-defi": {
      "command": "npx",
      "args": ["-y", "@waiaas/mcp"],
      "env": {
        "WAIAAS_BASE_URL": "http://127.0.0.1:3100", 
        "WAIAAS_AGENT_ID": "019c4cd2-86e8-758f-a61e-9c560307c788",
        "WAIAAS_AGENT_NAME": "defi-manager"
      }
    }
  }
}

Each agent sees only its assigned wallet and tools. Perfect for specialized trading bots or portfolio managers.

Real-World Example: DeFi Portfolio Manager

Here’s what happens when you ask Claude to “optimize my DeFi yield”:

  1. Assessment: Claude calls get-defi-positions to see your current lending/staking
  2. Analysis: Compares yields across Aave, Lido, Kamino using get-provider-status
  3. Strategy: Identifies better opportunities (e.g., “Your USDC earns 3% on Aave, but Kamino offers 5.2%”)
  4. Execution: Calls action-provider to withdraw from Aave and deposit to Kamino
  5. Confirmation: Uses get-transaction to verify completion

All in natural conversation. No switching apps, no manual transaction building.

Security Without Friction

WAIaaS enforces 21 policy types across 4 security tiers:

  • INSTANT: Small amounts (under $10) execute immediately
  • NOTIFY: Medium amounts ($10-$100) execute with notifications
  • DELAY: Large amounts ($100-$1000) wait 5 minutes (cancellable)
  • APPROVAL: Very large amounts (over $1000) require human approval

The policy engine uses default-deny enforcement. Without explicit ALLOWED_TOKENS or CONTRACT_WHITELIST policies, transactions are blocked. Your agent can’t accidentally drain funds or interact with malicious contracts.

For approval-tier transactions, Claude shows you the details and waits. You approve via WalletConnect, Telegram, or push notification. The agent then completes the workflow.

What’s Next

You’ve got 45 MCP tools and production-grade wallet infrastructure. Start with simple balance checks and token transfers, then explore DeFi automation as you get comfortable.

The MCP ecosystem is growing fast — WAIaaS puts you at the intersection of AI and onchain activity. Ready to give your Claude agent a wallet? Check out the complete setup guide at https://github.com/minhoyoo-iotrust/WAIaaS or explore the full documentation at https://waiaas.ai.

Back to the terminal — I built an invoicing tool that lives where you work

I love my terminal. It keeps me focussed and efficient. And it may sound silly, but it also makes me feel like I’m part of a community.

In a world increasingly shaped by LLMs and AI agents, I’ve found myself feeling nostalgic for the basics.

That’s why, for all my freelancer CLI-friends who struggle with context-switching; hate the complexity of today’s invoicing tools; or simply like the idea of more CLI <3, I have created Billed.

All you need to do is to run npm i billed and get started with bill --init-config.

It’s all run locally, there are no integrations needed and you can customise.

I’d love to know what you think!

Sub-Agent Documents Everything in Notion

The Prompt that birthed Escriber

I have a problem. Not a “my code does not compile” problem. A “I have so many ideas and projects and notes that my brain just gives up and reboots” problem. 😵‍💫

So I did what any reasonable developer would do: I built an AI agent inside Open Claw whose only job is to document everything beautifully in Notion. His name is Escriber.

The Prompt that birthed Escriber

This is my submission for the Notion MCP Challenge. Let me tell you, building a focused single-purpose agent with 14 Notion tools is exactly as satisfying as it sounds.

What I Built

Escriber is agent #2 of 5 on my OpenClaw multi-agent team.

Escriber telling me about himself

His SOUL.md says exactly this: “I document. Beautifully. In Notion.” And for anyone who has not used OpenClaw, they give these agents Soul.md files that define who the agent is and give them a small personality.

That is it. Full stop. He cannot debug your code. He cannot give life advice. He has one lane and he stays in it — which, honestly, is more discipline than I have most the time. 😆

He lives in Discord as a bot or I can use the web chat interface to call on him directly. He can be slightly artisanal. Dry wit is baked in by design, because documentation does not have to be soulless. He makes use of my Synap bot to write summaries for projects and clean them up like I would say them, then he will store what Synap sends back.

He is not a Swiss Army knife. He is a scalpel. And sometimes that is exactly what you need.

Video Demo

Show Us the Code

Escriber talks to Notion through mcporter — an MCP relay that proxies tool calls to Notion’s official MCP server. Every Notion interaction looks like this:

mcporter call notion.<tool_name> --args '{ ... }'

Clean. Consistent. One pattern to rule them all.

Here is the full arsenal — 14 tools, one agent, zero excuses for undocumented projects:

Tool What It Does
notion.search Find existing pages/databases before creating duplicates
notion.create_page Spin up a new page anywhere in the workspace
notion.retrieve_page Read a page’s metadata
notion.update_page Update page properties
notion.append_block_children Add content blocks to an existing page
notion.retrieve_block_children Read what is already on a page
notion.retrieve_block Fetch a specific block
notion.update_block Edit an existing block
notion.delete_block Remove a block
notion.create_database Create a new database
notion.retrieve_database Read database structure
notion.update_database Modify database schema
notion.query_database Filter and search database entries
notion.create_database_item Add a row to a database

Escriber also has workflow rules baked into his instructions. Because tools without discipline are just chaos with an API:

  • Search first. Always check if the page already exists before creating a new one.
  • Read before writing. Retrieve block children before appending to avoid structural disasters.
  • Right block type. Callouts for decisions. Toggles for details. Headings for structure. Not everything is a paragraph.
  • Structure intentionally. Measure twice, cut once. 🤣

How I Used Notion MCP

Let me tell you how this actually works.

mcporter connects Escriber to Notion’s official MCP server at https://mcp.notion.com/mcp. Every tool call gets proxied through that relay — no direct API wrangling, no custom request builders. The MCP layer handles it. Escriber just speaks tool.

Here is what that looks like day-to-day:

New project starts?
create_page to spin up the project hub. create_database_item to log it in the master projects database. Done in seconds.

Wrapping up a build session?
append_block_children to the existing project page. Build notes, decisions made, what broke, what did not. Structured. Timestamped. Actually findable later.

JB’s Job Listings
create_page My recruiter agent stored a list of jobs using Esciber every morning. Future-me will be grateful. Past-me was not doing this. These are stored in Notion daily, and sortable ☠️

Notion Job Notes

Let me tell you about the shame moment that made this real.

I went back through my own Notion workspace a few weeks ago. Pages with titles like “ideas v3 FINAL” and “project notes DO NOT DELETE” containing exactly… three bullet points and a YouTube link. That is it. That is the legacy. A graveyard of good intentions. ☠️

Escriber exists because I needed someone with more documentation discipline than me. Turns out that someone is a focused AI agent with a soul file and 14 Notion tools.

One job. One lane. Real personality. And the docs actually get written now.

“Optimization starts with a single point of failure—or a single point of success. Own the lane.”

Also, thanks to Bloggy, for taking the time to help with this post.

Escriber is part of my OpenClaw agent team. If you are curious about building multi-agent setups in openclaw, drop a comment — I am writing more about this whole stack as it comes together.

How I Tried to Handle Customer Support in Telegram and Ended Up Building a Tool for It

This didn’t start as a startup idea. I wasn’t trying to build a SaaS product. I just needed a simple way to handle customer support for my own projects without exposing my personal Telegram account or dealing with complex tools.

At first, Telegram felt perfect. Everyone already uses it, there’s no onboarding, no friction, no extra accounts. A client just sends a message and you reply. It’s fast, natural, and works out of the box.

And for a while, it really does work.

The problems don’t show up immediately. In the beginning, you have a few conversations per day, everything is manageable, and you can keep context in your head. Then you launch another project. Then another. Messages start coming in at different times, from different people, about different things.

You reply from your personal account, then maybe create a separate work account, then start forwarding messages to yourself or teammates. Over time, Telegram turns into a mix of personal chats, client conversations, and random forwarded messages. It becomes harder to understand what’s going on at any given moment.

The tricky part is that it doesn’t break in an obvious way. It slowly degrades. Responses get delayed, some messages are missed, sometimes two people reply to the same client, sometimes no one replies because everyone assumes someone else already did. Nothing critical, but enough to hurt the overall experience.

I tried a few workarounds. Multiple accounts, groups, pinned messages, manual labeling, forwarding flows. All of them help a bit, but none of them solve the core issue. Telegram is just a list of chats. There is no structure, no clear overview, no shared context.

Switching to a CRM or helpdesk didn’t feel right either. Not because those tools are bad, but because they’re often overkill for small teams or solo projects. You get dashboards, ticket statuses, workflows, onboarding, and another system you need to constantly keep open. Meanwhile, your actual communication still happens in Telegram, just routed through something else.

At some point it became clear that I didn’t need another tool. I needed a way to make Telegram itself more structured.

The idea ended up being very simple. Instead of clients messaging me directly, they message a bot. Every incoming message is forwarded into a private Telegram group where each client gets their own thread. One client, one thread. All history stays in one place, no forwarding, no confusion.

You reply directly inside that thread, and the bot sends the response back to the client.

Nothing fundamentally changes from the user’s perspective. It still feels like a normal Telegram chat. But internally, everything becomes structured. You can immediately see all active conversations, understand which ones need attention, and multiple people can work in parallel without stepping on each other.

Most importantly, your personal account is no longer part of the support flow at all.

I originally built this just to solve my own problem. But after using it for a while, I realized this pattern applies to a lot of people. Freelancers, small teams, indie projects, small businesses. Many of them rely on Telegram for communication, run into the same limitations, and don’t want to switch to heavy tools.

That’s how it turned into a small product.

If you’re curious how this approach works in practice, I put together a simple explanation here:

👉 https://gramdeskbot.com

It’s not trying to replace a CRM or compete with full helpdesk platforms. It’s just adding a missing layer to Telegram so it can function as a lightweight support system.

And in practice, for small setups, that turned out to be a much better fit than anything more complex.

If you’re already using Telegram as your main communication channel, you’ll likely run into the same issues at some point. The question is whether you keep patching it manually or introduce a bit of structure on top of what you already use.

RustCheat: A Minimal CLI Cheat Sheet for Rust

It’s been a little while since I really used Rust. Understanding this, I Noticed I forgot some of my syntax. Usually when I forget syntax I do a “quick” google search which might take me down a rabbit hole of where I either get distracted or need to google a bunch of other things. so I created a simple cli app so that for little things I never have to leave my terminal

DISCLAIMER this is my first cli app that I’ve published to a registry so any constructive criticism would be appreciated. the original cheatsheet that I had inspiration from was by Francesco Ciulla.

Rust Cheat Crate

If you would like to contribute to this project you can checkout the repo here thanks so much for your contribution!

NoxKey — A macOS Secrets Manager With Touch ID and AI Agent Detection

We were debugging a Stripe integration at 1am when Claude printed a live API key in its debug output. Full key. Right there in the conversation log.

The agent was not malicious. The system was broken. The secret sat in a .env file. The agent read the file and included the value in its response. That is what agents do — they read project files and use what they find. The .env file was the vulnerability, not the agent.

That night we started building NoxKey.

A macOS secrets manager built for developers

NoxKey is a macOS menu bar app and CLI that stores secrets in the macOS Keychain, protected by Touch ID. No cloud. No accounts. No subscription. Your secrets live in Apple’s encrypted storage on your machine and nowhere else.

When an AI agent requests a secret, NoxKey detects it automatically and delivers the value through an encrypted handoff — the secret reaches the agent’s process environment without ever appearing in its conversation context.

Keychain storage. Touch ID authentication. Encrypted handoff for AI agents.

0
cloud connections

30s
to install


0
config needed

Architecture: menu bar app + CLI over a Unix socket

NoxKey has two pieces:

Menu Bar App
SwiftUI · Native macOS

Touch ID

Agent Detection

Keychain Access

Session Manager

Unix
Socket

CLI
Swift · /usr/local/bin/noxkey

get / set / ls

import / unlock

peek / strict

Encrypted Handoff

macOS Keychain

The menu bar app is a native SwiftUI application. It manages the Keychain, handles Touch ID prompts, performs process-tree agent detection, and serves requests over a Unix domain socket. This is the server. It has Keychain entitlements, biometric access, and full control over what gets returned to whom.

The CLI (noxkey) talks to the menu bar app over that Unix socket. It does not touch the Keychain directly — every request goes through the server, which validates the caller independently.

Why a Unix socket instead of XPC or HTTP? Unix sockets provide LOCAL_PEERPID — the kernel tells the server exactly which process connected. No authentication tokens to manage. No port conflicts. No network exposure. The socket file lives at a user-specific path, accessible only to your user account.

Install this macOS secrets manager in 30 seconds

$ brew install no-box-dev/noxkey/noxkey

==> Downloading noxkey-0.6.43.tar.gz
==> Installing noxkey
==> Caveats
NoxKey menu bar app installed to /Applications.
CLI installed to /usr/local/bin/noxkey.
==> Summary
  /Applications/NoxKey.app
  /usr/local/bin/noxkey

Launch NoxKey.app from your Applications folder. It appears in the menu bar — a small key icon. That is the server running. The CLI works immediately.

$ noxkey --version
noxkey 0.6.43

No account creation. No master password. No onboarding wizard. It uses your existing macOS login Keychain and your existing fingerprint.

Replace your .env files with Keychain storage

If you have dozens of .env files scattered across your machine, the first step is importing them.

$ noxkey import myorg/api .env
[Touch ID prompt]
Imported 6 secrets:
  myorg/api/STRIPE_KEY
  myorg/api/DATABASE_URL
  myorg/api/REDIS_URL
  myorg/api/CLOUDFLARE_TOKEN
  myorg/api/SENDGRID_KEY
  myorg/api/JWT_SECRET

$ noxkey ls myorg/api/
  myorg/api/CLOUDFLARE_TOKEN
  myorg/api/DATABASE_URL
  myorg/api/JWT_SECRET
  myorg/api/REDIS_URL
  myorg/api/SENDGRID_KEY
  myorg/api/STRIPE_KEY

$ rm .env

Secrets are organized as org/project/KEY. One secret, one location, accessible from any terminal in any project directory. No more duplicating the same Cloudflare token across six repos.

Daily usage: Touch ID for every API key access

The core pattern is one line:

$ eval "$(noxkey get myorg/api/STRIPE_KEY)"
[Touch ID prompt]
$ echo $STRIPE_KEY
sk_live_...  # available in your shell environment

Touch ID fires. The secret loads into your shell environment. Your script or application reads it from $STRIPE_KEY like any environment variable.

Session unlock eliminates friction
For batch operations — say you need five secrets to run your dev server — run noxkey unlock myorg/api once with Touch ID. All subsequent get calls under that prefix skip biometric auth for a configurable window. The session is bound to your PID and process start time, so PID recycling cannot hijack it.

Need multiple secrets at once? Session unlock handles that:

$ noxkey unlock myorg/api
[Touch ID prompt — once]
Session unlocked for myorg/api/* (expires in 15 minutes)

$ eval "$(noxkey get myorg/api/STRIPE_KEY)"    # no Touch ID
$ eval "$(noxkey get myorg/api/DATABASE_URL)"   # no Touch ID
$ eval "$(noxkey get myorg/api/REDIS_URL)"      # no Touch ID

One fingerprint, then flow. The session is bound to your process ID and its start time — PID recycling cannot hijack it.

For your most sensitive secrets, strict mode overrides sessions:

$ noxkey strict myorg/api/STRIPE_KEY
# This key ALWAYS requires Touch ID, even during an active session

How AI agent detection works

When Claude Code runs noxkey get, you do not configure anything. Detection is automatic.

noxkey PID 61023 — get myorg/api/STRIPE_KEY    └─ zsh PID 61020 — spawned shell      └─ node PID 58401 — Claude Code runtime        └─ claude PID 58399 — MATCH! Agent detected Encrypted Handoff ← AES-256-CBC → temp script → source → self-delete Result: $STRIPE_KEY in shell env. Raw value never in conversation context.

The agent can make API calls, run your test suite, and deploy your app. It just cannot see, log, or echo the raw secret value. If it tries to use --raw or --copy, the CLI blocks it.

The six most common agent leak patterns — reading .env files, echoing secrets in debug output, storing values in conversation logs, hardcoding them in generated code, passing them to spawned processes — are all mitigated by this approach.

Security, DX, and agent safety features

Security

&#x1F91A;
Touch ID on every access

Not a password, not a PIN. Your fingerprint. Every time.

&#x1F512;
macOS Keychain storage

Apple’s Data Protection Keychain, backed by the Secure Enclave. Not a custom vault.

&#x1F6AB;
Zero network connections

NoxKey never phones home. No telemetry, no sync. Your secrets never leave your machine.

&#x1F6E1;
Strict mode

High-value secrets always require Touch ID, even during unlocked sessions.

&#x1F6A8;
DLP guard

Scans agent output for leaked secret values using 8-character fingerprints. Blocks leaks before they enter AI context.

Developer experience

&#x26A1;
One command

eval "$(noxkey get org/proj/KEY)"

&#x1F513;
Session unlock

One Touch ID, then batch operations flow without interruption.

&#x1F4E5;
.env import

noxkey import org/proj .env — migrate in one step.

&#x1F440;
Peek

noxkey peek org/proj/KEY — first 8 characters for verification, without exposing the full value.

&#x1F4C1;
Org/project hierarchy

Secrets are namespaced, searchable, and never duplicated across projects.

&#x1F5A5;
Menu bar UI

Browse, add, edit, and organize secrets without touching the terminal.

AI agent security

&#x1F916;
Automatic agent detection

Process-tree walking identifies Claude, Cursor, Codex, Windsurf, Copilot, and others.

&#x1F510;
Encrypted handoff

Agents get secrets in their process environment, never in conversation context.

&#x1F6D1;
Command blocking

--raw, --copy, load, export, bundle, env are all blocked for agent callers.

&#x1F50D;
DLP scanning

Catches leaked values in agent output before they persist.

What NoxKey does not do

Deliberate scope
NoxKey is for individual developers on macOS who need to keep API keys and tokens out of .env files and AI agent contexts. It is not a team vault, not cross-platform, not a password manager, and has no cloud sync.

Not a team tool. NoxKey is for individual developers. No shared vault, no role-based access, no audit log. For team secret management, look at Doppler or HashiCorp Vault.

Not cross-platform. macOS only. The security model depends on the macOS Keychain, Touch ID, and the Secure Enclave. These do not exist on Linux or Windows. The concepts are portable — this implementation is not.

Not a password manager. NoxKey manages developer credentials — API keys, tokens, database URLs, webhook secrets. It does not autofill browser forms or sync across devices. Use 1Password or Bitwarden for that.

No cloud sync. Your secrets exist on one machine. If your laptop dies, you re-import. This is a feature — no server to breach, no sync protocol to exploit, no third party with your data. Backups are your responsibility.

Why we built a dotenv alternative for macOS

We were using .env files like everyone else. We had a .gitignore entry. We thought we were fine.

Then AI coding assistants became part of the daily workflow. Every project file became fair game for an agent to read, reference, and include in responses. The .env file went from “slightly risky convenience” to “active liability.” The dotenv pattern was designed in 2012, before AI agents existed. It assumes the only thing reading your project files is your code.

We looked at existing options. 1Password CLI is solid but requires a subscription and has no agent detection. HashiCorp Vault targets infrastructure teams, not solo developers. Doppler is cloud-hosted. None of them distinguish between a human caller and an AI agent.

The macOS Keychain was sitting right there. Encrypted. Biometric. Local. Already on every Mac. All it needed was a developer-friendly interface and awareness of AI agents.

Get started

brew install no-box-dev/noxkey/noxkey

Free. No account. No cloud. Your Keychain and your fingerprint.

Key Takeaway
NoxKey stores your secrets in the macOS Keychain with Touch ID protection and zero cloud connections. When an AI agent requests a secret, process-tree detection delivers the value through an encrypted handoff — the secret reaches the agent’s shell environment without appearing in its conversation context. Install with brew install no-box-dev/noxkey/noxkey and your .env files become obsolete.

Read more: how we migrated 47 .env files, how Touch ID protects your API keys, or six ways AI agents leak secrets.

noxkey.ai

Frequently asked questions

*What is NoxKey?*
NoxKey is a free, open-source macOS menu bar app that stores developer secrets (API keys, tokens, passwords) in the macOS Keychain with Touch ID. It replaces .env files with hardware-encrypted storage and adds AI agent detection with encrypted handoff.

*How does NoxKey detect AI agents?*
NoxKey walks the macOS process tree when a secret is requested. If it detects an AI agent (Claude Code, Cursor, Copilot) in the calling chain, it switches to encrypted handoff — the secret reaches the agent’s shell environment through a self-deleting encrypted script, never entering the conversation context.

*Is NoxKey free?*
Yes. NoxKey is MIT-licensed, open source, and completely free. No account, no subscription, no cloud. Install with brew install no-box-dev/noxkey/noxkey.

*How do I migrate from .env files?*
One command: noxkey import myorg .env. This imports all key-value pairs into the macOS Keychain. Then delete the .env file. Access secrets with eval "$(noxkey get myorg/KEY)".

*Does NoxKey send data to the cloud?*
No. NoxKey makes zero outbound network connections. All secrets are stored locally in the macOS Keychain, which uses Apple’s Secure Enclave for hardware encryption. This is verifiable via macOS network monitoring.

*What’s the difference between NoxKey and 1Password CLI?*
NoxKey is local-only (no cloud, no account), free, and includes AI agent detection with encrypted handoff. 1Password CLI requires a cloud subscription and has no AI-specific security features. Full comparison.

NoxKey is free and open source. brew install no-box-dev/noxkey/noxkey — GitHub | Website

Stop Putting API Keys in .env Files — Use Your OS Keychain Instead

Last year, a developer at a YC startup pushed a .env file to a public GitHub repo. It contained their Stripe live key, an OpenAI API key, and a production database URL. Automated scanners picked it up in under 30 seconds. By the time GitHub’s secret scanning revoked the tokens it recognized, someone had already racked up $14,000 in OpenAI API charges.

This is not rare. GitGuardian’s 2024 State of Secrets Sprawl report found 12.8 million new secrets exposed in public GitHub repositories in a single year. A 28% increase from the year before. And those are just the public repos — private ones are worse, because nobody is scanning them.

12.8M
secrets exposed in public repos (2024)

28%
increase year over year

Your .env file is a liability. Here is why, and what to do about it.

The dotenv pattern was never a security mechanism

The dotenv pattern came out of the Ruby community in 2012. It solved a real problem: developers were hardcoding database passwords and API keys directly into source files. Moving them to a separate file that you .gitignore was a genuine improvement.

But here is what a typical .env looks like on a developer’s machine right now:

OPENAI_API_KEY=sk-proj-abc123...
STRIPE_SECRET_KEY=sk_live_...
DATABASE_URL=postgresql://admin:[email protected]:5432/main
CLOUDFLARE_API_TOKEN=v4x...
AWS_SECRET_ACCESS_KEY=wJalrXUtnFEMI...

Five production credentials. Plaintext. No authentication to read them. No encryption at rest. No audit trail. Any process running as your user — a rogue npm postinstall script, a compromised VS Code extension, a careless docker build — can read that file without you knowing.

That is not security. That is a Post-it note on your monitor with the vault combination.

Why .env file security breaks down at scale

A single .env file is manageable. Nobody has a single .env file.

We counted ours. 47. Some in active projects, some in archived repos, some in Docker contexts that got copied into images. The same Cloudflare API token appeared in six different files. When we rotated it, we updated three and missed the other three for weeks. (Full story of that audit here.)

There is no expiry tracking. No way to know which secrets are still valid. No audit trail of which process read which key. When a breach happens, incident response starts with “wait, where do we even have this key?” and ends with grep -r across the entire home directory.

Warning
GitHub’s push protection auto-revokes tokens from GitHub, AWS, Google Cloud, and a handful of other providers. But most services lack that integration. Your Stripe key, your Postmark token, your custom API credentials — if those hit a public repo, nobody revokes them automatically. You find out when the bill arrives or the data is gone.

AI agents turned .env files into a critical vulnerability

The .env pattern assumed that only your application would read the file. That assumption broke in 2025.

AI coding agents — Claude Code, Cursor, GitHub Copilot, Codex — routinely read project files to build context. Your .env is a project file. When an agent reads it, every secret in that file enters the model’s context window. From there, values can appear in generated code, debug output, error messages, or conversation logs.

The agent is not being malicious. It is trying to help. “Here is the error — your DATABASE_URL returns connection refused” — and now your production database hostname and credentials are in the chat history. Shared with your team. Logged by the provider. Potentially used as training data.

We wrote more about specific leak vectors in 6 Ways AI Agents Leak Your Secrets. The short version: if a secret is in a file that an agent can read, assume it will be read.

The env file alternative: macOS Keychain with Touch ID

The macOS Keychain is an encrypted credential store that has been on every Mac for over 20 years. It is backed by the Secure Enclave, protected by Touch ID, and used by Safari, SSH, and every Apple-signed application. Not a startup’s custom vault — infrastructure that Apple maintains and audits.

NoxKey is a thin layer on top of the Keychain, purpose-built for developer secrets:

Before: plaintext .env
# Plaintext file anyone can read
$ cat .env
STRIPE_SECRET_KEY=sk_live_51Hx...
After: Keychain + Touch ID
# Encrypted in Keychain, Touch ID on every access
$ noxkey set myorg/project/STRIPE_KEY --clipboard
✓ Stored myorg/project/STRIPE_KEY

$ eval "$(noxkey get myorg/project/STRIPE_KEY)"
# → Touch ID prompt → secret loaded into shell
# → raw value never written to disk

$ echo $STRIPE_KEY
sk_live_51Hx...

One secret, one location, accessible from any project directory. No files on disk. Touch ID every time. When an AI agent calls noxkey get, it detects the agent’s process tree and returns an encrypted handoff instead of the raw value — the secret reaches the environment but never enters the conversation context.

Agent calls noxkey get → Process tree detected → AES-256-CBC encryption → Secret in env, never in context

Migrate from .env to Keychain in minutes

# Import your existing .env file
$ noxkey import myorg/project .env
✓ Imported 5 secrets

# Verify everything landed
$ noxkey ls myorg/project/
myorg/project/STRIPE_SECRET_KEY
myorg/project/OPENAI_API_KEY
myorg/project/DATABASE_URL
myorg/project/CLOUDFLARE_API_TOKEN
myorg/project/AWS_SECRET_ACCESS_KEY

# Peek at a value to confirm (shows first 8 chars)
$ noxkey peek myorg/project/STRIPE_SECRET_KEY
sk_live_...

# Now delete the liability
$ rm .env

Do that for every project. We did 47 in one afternoon. The find command that started it:

$ find ~/dev -name ".env" -not -path "*/node_modules/*" -not -path "*/.git/*" | wc -l
47

What about CI/CD?

This approach is for local development — your machine, your secrets, your Touch ID. CI/CD systems have their own secrets management: GitHub Actions secrets, Cloudflare environment variables, AWS Parameter Store, Vault. Those are purpose-built for that environment and they work.

The problem is the gap between “secrets managed in CI” and “secrets on your laptop.” That gap is currently filled by plaintext files with no authentication, no encryption, and no access control. It should be filled by your operating system’s credential store.

The honest tradeoffs of leaving dotenv behind

This is macOS only. If your team is on Linux or Windows, NoxKey is not the answer for them (though the principle holds — use your OS credential store, not plaintext files).

There is friction. Touch ID on every access means authenticating more than before. Session unlock (noxkey unlock myorg/project) reduces this to one authentication per batch, but it is still more than the zero authentication that .env offers. That friction is the point — it means something is actually guarding access.

You will need to update your workflow. Instead of copying .env.example and filling in values, you run noxkey import once and use eval commands. It took us about a day to stop reaching for .env instinctively.

Your API keys deserve better than plaintext files

12.8 million secrets exposed in public repos last year. AI agents reading every file in your project directory. Supply chain attacks targeting plaintext credentials. The .env pattern was a good idea in 2012. It is a liability in 2026.

Your operating system has an encrypted, hardware-backed credential store with biometric authentication. Use it.

Key Takeaway
Your .env file has no encryption, no authentication, and no access control. Every AI agent, every rogue script, and every accidental git push can read it. Move your secrets to the macOS Keychain — one location, Touch ID on every access, and AI agents never see the raw values. The migration takes minutes per project.

brew install no-box-dev/noxkey/noxkey

Free. No account. No cloud. Your secrets stay on your machine.

Frequently asked questions

*Why are .env files insecure?*
.env files store secrets as plaintext on disk with no encryption, no authentication, and no access control. Any process, script, or AI agent with file system access can read them. They frequently get committed to git — 12.8 million secrets were exposed on GitHub in 2024.

*What should I use instead of dotenv?*
Use your operating system’s credential store. On macOS, the Keychain provides hardware-encrypted storage with Touch ID authentication. NoxKey wraps the Keychain in a developer-friendly CLI: eval "$(noxkey get myorg/KEY)" replaces process.env.KEY.

*Can AI agents read .env files?*
Yes. AI coding tools like Claude Code, Cursor, and Copilot have file system access and can read any .env file in your project directory. NoxKey prevents this by storing secrets in the Keychain and delivering them through encrypted handoff when an AI agent is detected.

*How do I migrate from .env to the macOS Keychain?*
Install NoxKey (brew install no-box-dev/noxkey/noxkey), then run noxkey import myorg .env to move all secrets to the Keychain. Delete the .env file afterward. The migration takes about a minute per project.

NoxKey is free and open source. brew install no-box-dev/noxkey/noxkey — GitHub | Website

Getting Started with Seal Report: Static and Dynamic Select Lists

vladg_dev profile

This is the third post in the series.

In the previous post, we created a pivot table with custom filters. While those filters allowed us to apply constraints such as Equals, Contains, and Between, it would be useful to extend the example further by introducing static and dynamic select lists as filtering options.

In this post, we will enhance the existing solution by integrating these select lists and exploring how they improve the filtering experience.

Below is the link to the previous post:

Adding a Static Enumeration

In the context of Seal Report, a static enumeration is a collection of key-value pairs defined directly in the report’s XML document definition.

For example, instead of retrieving the distinct values of PayFrequency from the HumanResources.EmployeePayHistory table, it is often more efficient to store these values directly in the data model used for rendering the report. Even executing a hardcoded SQL query each time the report runs would be less efficient than using a predefined collection.

In this case, the static enumeration behaves like a constant list that is already available at runtime and does not require additional database queries.

Select the Add Enum option available under Sources → Data Source → Enumerated Lists. A contextual configuration panel will appear on the right side.

Within the enum definition, provide a meaningful Name, and configure the following options if needed:

  • whether the list is dynamically loaded from a SQL Select Statement or from a Load Script

  • whether the list should be refreshed before report execution

  • whether the list values depend on the connection.

These settings allow you to control how enumeration values are loaded and updated during report execution.

For the current scope, all these options remain set to False, since we are defining a static enumeration.

The SQL Select Statement used to define the enumeration values is the following:

SELECT *
FROM (VALUES
    (1, 'Monthly'),
    (2, 'Biweekly')
) AS PayFrequencyEnum([Key], [Value])

The enum’s configuration looks this way:

Static Enum Configuration

Note that the Refresh values option may not appear immediately in the UI. If it is not visible, reopen the enum definition or temporarily enable a dynamic loading option so the two values become available in the final collection.

The enumeration created in the UI is persisted in the report definition as a <MetaEnum> element. A simplified example looks like this:

<MetaEnum>
  <GUID>a90b0ce6-bde8-4199-8869-f2ce0c1218ce</GUID>
  <Name>PayrollFrequency</Name>
  <Sql>SELECT *
FROM (VALUES
    (CAST(1 AS INT), 'Monthly'),
    (CAST(2 AS INT), 'Biweekly')
) AS PayFrequencyEnum([Key], [Value])</Sql>
  <Values>
    <MetaEV>
      <Id>1</Id>
      <Val>Monthly</Val>
    </MetaEV>
    <MetaEV>
      <Id>2</Id>
      <Val>Biweekly</Val>
    </MetaEV>
  </Values>
</MetaEnum>

If the enumeration is configured as static, the actual values used at runtime are stored inside the <Values> section. In this case, the <Sql> element is not required for execution and mainly serves as a definition template.

You can even remove the <Sql> element and keep only the <Values> collection to preserve the same static behavior.

Adding a Dynamic Enumeration

For a dynamic enumeration, let’s select a set of properties directly from the database that are expected to change over time.

For example, the HumanResources.EmployeeDepartmentHistory table references the HumanResources.Shift table. This means that the available shift values may change in the future as new shifts are added or existing ones are modified.

In such scenarios, using a dynamic enumeration ensures that the list of available values is always loaded from the database and reflects the current state of the data.

For this particular case, the list will be dynamically loaded from the SQL Select Statement, and its values will depend on the connection.

I’ve chosen the following SQL Select Statement:

SELECT 
    [ShiftID] AS [KEY],
    CONCAT(
        [Name], 
        ' (',
        FORMAT(CAST([StartTime] AS datetime2), 'HH:mm'),
        ' - ',
        FORMAT(CAST([EndTime] AS datetime2), 'HH:mm'),
        ')'
    ) AS [VALUE]
FROM [AdventureWorks2025].[HumanResources].[Shift]

The configuration looks the following way:

Dynamic Enum Configuration

The enumeration will be reflected in the report definition like this:

<MetaEnum>
            <GUID>c107bf33-5f3a-4f26-908d-48a8f768d0d9</GUID>
            <Name>Shifts</Name>
            <IsDynamic>true</IsDynamic>
            <ValuesPerConnection>true</ValuesPerConnection>
            <Sql>SELECT 
    [ShiftID] AS [KEY],
    CONCAT(
        [Name], 
        ' (',
        FORMAT(CAST([StartTime] AS datetime2), 'HH:mm'),
        ' - ',
        FORMAT(CAST([EndTime] AS datetime2), 'HH:mm'),
        ')'
    ) AS [VALUE]
FROM [AdventureWorks2025].[HumanResources].[Shift]</Sql>
          </MetaEnum>

Note that the report definition may also include a key–value collection inside a <Values> section. This typically appears after selecting Refresh values or pressing F9, which materializes the current enumeration entries in the report model.

Applying Enumerations on Restrictions

The process of applying a select-based filter is very similar to the one used for expression-based filters. The key difference is that, within the Advanced section, you must select the appropriate Custom enum.

Drag and drop the PayFrequency property from the HumanResources.EmployeePayHistory table into the Restrictions section. Then click on the newly created [PayFrequency Equals] expression. In the contextual panel on the right side, navigate to the Advanced section and select the PayrollFrequency enumeration.

Execute the report, and you will see the available filters as shown in the screenshot below.

Mapping Restriction with an Enumeration

It does not matter whether the enumeration is static or dynamic — both are applied in the same way when configuring a restriction or filter.

Skill Check

Apply the Shifts enumeration to the ShiftID property from the HumanResources.Shift table. The process is similar to the one discussed in the previous section.

Hint: combine restrictions using both the PayrollFrequency and Shifts enumerations.

If you’ve configured it successfully, try answering the following questions:

  • How many employees from the Engineering department have agreed to a Biweekly payroll frequency and are working the Day shift (07:00 – 15:00)?

  • How many employees with a FirstName starting with Chris are assigned to either the Evening or Night shift?

Dependent select lists allow one enumeration to react dynamically to the selection of another. In one of the following posts, I will show you how to apply dependent select lists.

Quick Summary

Static vs Dynamic Enumerations

Feature Static Dynamic
Loaded at runtime ❌ No ✅ Yes
Requires SQL execution ❌ No ✅ Yes
Stored in <Values> ✅ Yes Optional
Reflects DB changes automatically ❌ No ✅ Yes
Depends on connection ❌ No Optional

Use static enumerations for constant lookup lists and dynamic enumerations when values must reflect the current database state.

How to Set Up Semgrep in 2026 – Complete Installation and Configuration Guide

Semgrep screenshot

Why Semgrep and why now

Semgrep is a fast, open-source static analysis tool that finds bugs and security vulnerabilities by letting you write rules that look like the code you are searching for. Unlike legacy SAST tools that require specialized security expertise to configure and produce overwhelming false positive rates, Semgrep was designed from the ground up for developers. Its pattern syntax mirrors your actual source code, its CLI runs in seconds, and its rule library covers over 30 programming languages with thousands of pre-written checks.

Since its launch by r2c (now Semgrep, Inc.) in 2020, Semgrep has become the default security scanner for thousands of engineering teams – from startups running the free open-source engine to enterprises using the full cloud platform. Dropbox, Figma, Snowflake, and Hashicorp all use Semgrep in their development pipelines. The tool scans over 100 million lines of code daily across its user base.

The reason to set up Semgrep now is straightforward. Every major compliance framework – SOC 2, PCI DSS 4.0, ISO 27001 – requires or strongly recommends static analysis in the development lifecycle. Semgrep gives you that compliance evidence while also catching real vulnerabilities. The open-source engine is free, and the full platform is free for teams of up to 10 contributors. There is no licensing cost barrier to getting started.

This guide walks through every step of setting up Semgrep – from installing the CLI on your local machine to running it in CI/CD pipelines with automatic PR comments. By the end, you will have a production-ready Semgrep configuration that catches security issues before they reach your main branch.

Semgrep screenshot

Step 1 – Install the Semgrep CLI

Semgrep provides three installation methods. Choose the one that fits your environment.

Install with pip (all platforms)

The pip installation is the recommended method and works on macOS, Linux, and Windows (via WSL). Semgrep requires Python 3.8 or later.

# Install Semgrep
pip install semgrep

# Verify the installation
semgrep --version

If you prefer to isolate Semgrep from your system Python, use pipx:

# Install with pipx for isolated environment
pipx install semgrep

# Verify
semgrep --version

Install with Homebrew (macOS)

On macOS, Homebrew provides a straightforward installation:

# Install via Homebrew
brew install semgrep

# Verify
semgrep --version

Install with Docker (any platform)

Docker is useful for CI environments or when you do not want to install anything on the host system:

# Pull the Semgrep image
docker pull semgrep/semgrep

# Run a scan using the Docker image
docker run --rm -v "${PWD}:/src" semgrep/semgrep semgrep --config auto /src

The Docker approach mounts your current directory into the container at /src and runs the scan against it. This method ensures a consistent environment regardless of the host operating system.

Verify your installation

After installing through any method, confirm that Semgrep is working:

semgrep --version
# Expected output: semgrep 1.x.x

If you see a version number, the installation was successful. If you encounter a “command not found” error, ensure that the installation directory is in your system PATH. For pip installations, this is typically ~/.local/bin on Linux or ~/Library/Python/3.x/bin on macOS.

Step 2 – Run your first scan

With Semgrep installed, you can run your first scan immediately without any configuration files.

Scan with the default rule set

Navigate to any project directory and run:

cd /path/to/your/project
semgrep --config auto

The --config auto flag tells Semgrep to automatically select rules that are relevant to the languages and frameworks detected in your project. Semgrep downloads the appropriate rules from the Semgrep Registry, runs the scan, and prints findings to your terminal.

Scan with a specific rule set

For more control over which rules run, specify a rule set by name:

# Run the default curated rule set
semgrep --config p/default

# Run security-focused rules
semgrep --config p/security-audit

# Run language-specific rules
semgrep --config p/python
semgrep --config p/javascript
semgrep --config p/golang

Scan a specific file or directory

You do not have to scan your entire project. Target specific paths:

# Scan a single file
semgrep --config p/default src/auth/login.py

# Scan a specific directory
semgrep --config p/default src/api/

# Scan multiple paths
semgrep --config p/default src/auth/ src/api/ src/middleware/

Understand the output

A typical Semgrep finding looks like this:

src/api/users.py
  security.python.sql-injection.sql-injection
    Detected string concatenation in SQL query. Use parameterized queries instead.

    14│ query = "SELECT * FROM users WHERE id = " + user_id

Each finding includes the file path, the rule ID that triggered the match, a human-readable message explaining the issue, and the exact line of code that was matched. The rule ID is important because you will use it later to customize which rules run and to suppress false positives.

Output in different formats

Semgrep supports multiple output formats for integration with other tools:

# JSON output for programmatic processing
semgrep --config p/default --json > results.json

# SARIF output for GitHub Code Scanning integration
semgrep --config p/default --sarif > results.sarif

# JUnit XML for CI/CD integration
semgrep --config p/default --junit-xml > results.xml

# Emacs/Vim compatible output
semgrep --config p/default --emacs

Step 3 – Understand Semgrep rule sets

Rule sets are collections of rules curated for specific use cases. Choosing the right rule sets determines what Semgrep looks for and how many findings you get.

Core rule sets

p/default is the starting point for most teams. It contains high-confidence security and correctness rules curated by the Semgrep team. These rules have low false positive rates and focus on issues that are almost always worth fixing. Start here and expand later.

p/security-audit is a broader security-focused set that includes rules with moderate confidence. It catches more potential issues but produces more findings that may require manual review. Use this when you want comprehensive security coverage and have the bandwidth to triage additional findings.

p/owasp-top-ten maps rules to the OWASP Top 10 vulnerability categories – injection, broken authentication, sensitive data exposure, and so on. This set is useful for compliance-driven teams that need to demonstrate OWASP coverage in their security program.

Language-specific rule sets

Semgrep provides curated rule sets for individual languages and frameworks:

Rule set Focus
p/python Python security and correctness
p/javascript JavaScript and Node.js security
p/typescript TypeScript-specific patterns
p/golang Go security and error handling
p/java Java security patterns
p/ruby Ruby and Rails security
p/csharp C# security patterns
p/php PHP security patterns
p/rust Rust safety and correctness

Infrastructure rule sets

For infrastructure-as-code scanning:

Rule set Focus
p/terraform Terraform misconfigurations
p/dockerfile Dockerfile security
p/docker-compose Docker Compose issues
p/kubernetes Kubernetes YAML security

Combining multiple rule sets

You can run multiple rule sets in a single scan by passing multiple --config flags:

semgrep --config p/default --config p/security-audit --config p/python

Start with p/default alone, review the findings, and then add additional sets incrementally. Adding too many rule sets at once can generate an overwhelming number of findings that make it hard to prioritize what to fix first.

Step 4 – Write custom Semgrep rules

One of Semgrep’s most powerful features is how easy it is to write custom rules. Unlike tools that require a proprietary query language, Semgrep rules use patterns that look like the code they are matching.

Basic rule structure

Create a file called custom-rules.yaml:

rules:
  - id: no-hardcoded-passwords
    patterns:
      - pattern: password = "$VALUE"
    message: >
      Hardcoded password detected. Use environment variables or a
      secrets manager instead of embedding credentials in source code.
    severity: ERROR
    languages:
      - python
    metadata:
      cwe:
        - "CWE-798: Use of Hard-coded Credentials"
      category: security

Every rule needs five required fields:

  • id – a unique identifier for the rule, used in output and for suppression
  • pattern or patterns – the code pattern to match, using metavariables like $VALUE as placeholders
  • message – a human-readable explanation shown when the rule matches
  • severity – one of ERROR, WARNING, or INFO
  • languages – an array of languages this rule applies to

Using metavariables

Metavariables are placeholders that match any expression. They start with $ and an uppercase name:

rules:
  - id: insecure-hash-algorithm
    patterns:
      - pattern: hashlib.$ALGO(...)
      - metavariable-regex:
          metavariable: $ALGO
          regex: (md5|sha1)
    message: >
      Insecure hash algorithm '$ALGO' detected. Use SHA-256 or
      stronger for cryptographic hashing.
    severity: WARNING
    languages:
      - python

This rule matches any call to hashlib.md5(...) or hashlib.sha1(...) regardless of the arguments passed.

Combining patterns with pattern-either and pattern-not

Use pattern-either to match multiple patterns and pattern-not to exclude safe patterns:

rules:
  - id: dangerous-eval
    patterns:
      - pattern-either:
          - pattern: eval($INPUT)
          - pattern: exec($INPUT)
      - pattern-not: eval("literal_string")
    message: >
      Use of eval() or exec() with dynamic input is a code injection
      risk. Consider using ast.literal_eval() or a safer alternative.
    severity: ERROR
    languages:
      - python

A more advanced example – detecting SQL injection

rules:
  - id: flask-sql-injection
    patterns:
      - pattern: |
          $CURSOR.execute("..." + $INPUT + "...")
      - pattern-not: |
          $CURSOR.execute("..." + "..." + "...")
    message: >
      SQL query built using string concatenation with variable input.
      Use parameterized queries with placeholders to prevent SQL injection.
      Replace: cursor.execute("SELECT * FROM users WHERE id = %s", (user_id,))
    severity: ERROR
    languages:
      - python
    metadata:
      cwe:
        - "CWE-89: SQL Injection"
      owasp:
        - "A03:2021 - Injection"

Testing your custom rules

Run your custom rules against your codebase:

# Run a single custom rule file
semgrep --config custom-rules.yaml

# Run custom rules alongside registry rules
semgrep --config custom-rules.yaml --config p/default

# Test a rule against a specific file
semgrep --config custom-rules.yaml src/database/queries.py

Organizing custom rules

For teams with multiple custom rules, organize them in a directory:

.semgrep/
  security/
    sql-injection.yaml
    auth-bypass.yaml
    secrets.yaml
  correctness/
    null-checks.yaml
    error-handling.yaml
  style/
    naming-conventions.yaml

Then scan with the entire directory:

semgrep --config .semgrep/

Step 5 – Set up Semgrep in GitHub Actions

Running Semgrep in CI ensures every pull request is scanned automatically. Here is how to set up a production-ready GitHub Actions workflow.

Basic GitHub Actions workflow

Create .github/workflows/semgrep.yml:

name: Semgrep

on:
  pull_request: {}
  push:
    branches:
      - main

jobs:
  semgrep:
    name: Semgrep Scan
    runs-on: ubuntu-latest
    container:
      image: semgrep/semgrep
    steps:
      - name: Checkout code
        uses: actions/checkout@v4

      - name: Run Semgrep
        run: semgrep ci
        env:
          SEMGREP_APP_TOKEN: ${{ secrets.SEMGREP_APP_TOKEN }}

This workflow runs Semgrep on every pull request and every push to the main branch. The semgrep ci command is designed for CI environments – it performs diff-aware scanning (only analyzing changed files on PRs), uploads results to Semgrep Cloud if a token is configured, and exits with a non-zero code if blocking findings are detected.

GitHub Actions without Semgrep Cloud

If you do not want to use Semgrep Cloud, you can run the scan using only the CLI with specific rule sets:

name: Semgrep

on:
  pull_request: {}
  push:
    branches:
      - main

jobs:
  semgrep:
    name: Semgrep Scan
    runs-on: ubuntu-latest
    container:
      image: semgrep/semgrep
    steps:
      - name: Checkout code
        uses: actions/checkout@v4

      - name: Run Semgrep
        run: semgrep scan --config p/default --config p/security-audit --error

The --error flag causes Semgrep to exit with a non-zero code when findings are detected, which fails the GitHub Actions check and blocks the PR from merging if branch protection is configured.

Adding SARIF upload for GitHub Code Scanning

To see Semgrep findings in GitHub’s Security tab alongside CodeQL results:

name: Semgrep

on:
  pull_request: {}
  push:
    branches:
      - main

jobs:
  semgrep:
    name: Semgrep Scan
    runs-on: ubuntu-latest
    container:
      image: semgrep/semgrep
    permissions:
      security-events: write
    steps:
      - name: Checkout code
        uses: actions/checkout@v4

      - name: Run Semgrep
        run: semgrep scan --config p/default --sarif --output semgrep-results.sarif

      - name: Upload SARIF
        uses: github/codeql-action/upload-sarif@v3
        with:
          sarif_file: semgrep-results.sarif
        if: always()

This uploads Semgrep results in SARIF format so they appear in the GitHub Security tab under “Code scanning alerts.” The if: always() ensures results are uploaded even when Semgrep finds issues and returns a non-zero exit code.

Configuring branch protection

After adding the Semgrep workflow, configure GitHub branch protection to require the scan to pass before merging:

  1. Go to your repository Settings, then Branches
  2. Edit the branch protection rule for your main branch
  3. Enable “Require status checks to pass before merging”
  4. Search for and add the “Semgrep Scan” check
  5. Save your changes

Now any PR with blocking Semgrep findings will be prevented from merging until the issues are resolved.

Step 6 – Connect Semgrep Cloud

Semgrep Cloud (the Semgrep AppSec Platform) adds a web dashboard, PR comments, AI-powered triage, and cross-file analysis on top of the open-source CLI. It is free for up to 10 contributors.

Create a Semgrep Cloud account

  1. Go to semgrep.dev and sign up with your GitHub, GitLab, or email account
  2. Create an organization that matches your GitHub organization
  3. Navigate to Settings and generate an API token
  4. Save this token – you will need it for CI configuration

Add the token to GitHub

  1. Go to your repository Settings, then Secrets and variables, then Actions
  2. Click “New repository secret”
  3. Name it SEMGREP_APP_TOKEN
  4. Paste the token from Semgrep Cloud
  5. Click “Add secret”

Configure scanning policies in Semgrep Cloud

Semgrep Cloud lets you manage rule configuration from the web dashboard instead of hardcoding rule sets in your CI file:

  1. In Semgrep Cloud, go to Policies
  2. You will see a default policy with recommended rules enabled
  3. Add or remove rule sets based on your needs
  4. Set rules to Comment, Block, or Monitor mode

When you use semgrep ci in your workflow (instead of semgrep scan --config ...), Semgrep pulls its configuration from the cloud policy. This means you can change what gets scanned and what severity levels block PRs without modifying your workflow file.

Rule modes in Semgrep Cloud

Semgrep Cloud supports three modes for each rule:

  • Block – findings from this rule fail the CI check and block the PR from merging
  • Comment – findings are posted as PR comments but do not block merging
  • Monitor – findings are tracked in the dashboard but are not surfaced on the PR at all

Most teams start with the majority of rules in Comment mode and only promote rules to Block mode after confirming they produce zero or near-zero false positives in their specific codebase.

Step 7 – Configure PR comments

PR comments are how Semgrep delivers findings to developers in their existing workflow – directly in the pull request where the code was changed.

How PR comments work

When Semgrep Cloud is connected and semgrep ci runs in your CI pipeline, it performs a diff-aware scan that analyzes only the code changed in the pull request. New findings are posted as inline comments on the exact lines of code where the issues were detected. Each comment includes the rule name, severity, a description of the issue, and often a suggested fix.

Install the Semgrep GitHub App

For PR comments to work, you need the Semgrep GitHub App installed:

  1. In Semgrep Cloud, go to Settings, then Source Code Managers
  2. Click “Add GitHub” and authorize the Semgrep GitHub App
  3. Choose which repositories or organizations to grant access to
  4. Confirm the installation

Once installed, any repository connected to Semgrep Cloud will receive inline PR comments when semgrep ci detects new findings.

Customizing comment behavior

In Semgrep Cloud under Settings, you can control:

  • Whether comments include fix suggestions
  • Whether to add a summary comment at the top of the PR
  • Whether to leave comments only for blocking findings or for all findings
  • Whether to automatically resolve comments when the underlying code is fixed

Example PR comment

A typical Semgrep PR comment looks like:

⚠️ semgrep: python.flask.security.injection.tainted-sql-string

Detected user input flowing into a SQL query without sanitization.
This is a SQL injection vulnerability.

Suggested fix: Use parameterized queries.
- cursor.execute("SELECT * FROM users WHERE id = " + request.args["id"])
+ cursor.execute("SELECT * FROM users WHERE id = %s", (request.args["id"],))

🔗 Rule details | 📘 CWE-89 | Triage in Semgrep Cloud

Developers can respond to findings directly in the PR – fixing the code, marking as false positive, or adding a # nosemgrep comment to suppress the finding with justification.

Step 8 – Set up .semgrepignore

The .semgrepignore file tells Semgrep which files and directories to skip during scans. This is essential for reducing noise from test files, generated code, vendored dependencies, and other paths where findings are not actionable.

Create a .semgrepignore file

Create a .semgrepignore file in your repository root:

# Test files - findings in tests are usually not exploitable
tests/
test/
*_test.go
*_test.py
test_*.py
*.test.js
*.test.ts
*.spec.js
*.spec.ts

# Generated code - cannot be fixed in source
generated/
__generated__/
*.generated.ts
*.gen.go

# Vendored dependencies - managed upstream
vendor/
node_modules/
third_party/

# Build artifacts
dist/
build/
out/
.next/

# Documentation and configuration
docs/
*.md
*.rst

# Migrations - often contain raw SQL by design
migrations/
alembic/

.semgrepignore syntax

The syntax follows .gitignore conventions:

  • directory/ ignores an entire directory and its contents
  • *.ext ignores all files with that extension
  • pattern ignores matching files anywhere in the tree
  • !pattern negates a previous ignore (force-includes a file)
  • # starts a comment line

When not to ignore

Be cautious about ignoring too much. Some common patterns to avoid ignoring:

  • Do not ignore configuration files. Security misconfigurations in Dockerfiles, Terraform files, and Kubernetes manifests are high-value findings.
  • Do not ignore migration files entirely. While raw SQL in migrations is expected, injection vulnerabilities can still appear when migrations accept dynamic input.
  • Do not ignore scripts/ or tools/ directories. Internal tooling often has weaker security standards and is a common source of vulnerabilities.

Step 9 – Advanced configuration

Beyond the basics, Semgrep supports several configuration options that help you tune scanning behavior for your codebase.

The semgrep.yaml configuration file

Create a .semgrep.yaml file in your repository root to set default scan options:

rules:
  - p/default
  - p/security-audit
  - .semgrep/

options:
  timeout: 30
  max-memory: 5000

Excluding specific rules

If a specific rule from a registry set produces too many false positives in your codebase, exclude it:

# Exclude specific rules by ID
semgrep --config p/default --exclude-rule "generic.secrets.gitleaks.generic-api-key"

Inline suppressions

Suppress individual findings with inline comments:

# nosemgrep: python.flask.security.injection.tainted-sql-string
cursor.execute("SELECT * FROM config WHERE key = " + safe_internal_key)

The nosemgrep comment accepts a rule ID to suppress only that specific rule on the annotated line. This is preferable to broad suppressions because it documents exactly which check was reviewed and accepted.

For other languages, the comment syntax follows the language convention:

// nosemgrep: javascript.express.security.injection.tainted-sql-string
db.query("SELECT * FROM config WHERE key = " + internalKey);
// nosemgrep: go.lang.security.injection.tainted-sql-string
db.Query("SELECT * FROM config WHERE key = " + safeKey)

Setting exit codes for CI

Control how Semgrep’s exit code maps to CI pass/fail behavior:

# Exit 1 only for ERROR severity findings
semgrep --config p/default --severity ERROR --error

# Exit 1 for WARNING and ERROR findings
semgrep --config p/default --severity WARNING --error

This lets you treat ERROR-level findings as blocking while allowing WARNING-level findings to be advisory.

Max target size and timeout

For large repositories, configure limits to prevent scans from hanging:

# Skip files larger than 1MB
semgrep --config p/default --max-target-bytes 1000000

# Set per-rule timeout to 30 seconds
semgrep --config p/default --timeout 30

# Set maximum memory usage
semgrep --config p/default --max-memory 5000

Step 10 – Troubleshooting common issues

Here are the most common problems teams encounter when setting up Semgrep and how to resolve them.

“command not found” after installation

If semgrep is not found after installing via pip, your Python scripts directory is not in your PATH:

# Find where pip installed Semgrep
python -m site --user-base
# Add the bin directory to your PATH
export PATH="$HOME/.local/bin:$PATH"

# Make it permanent by adding to your shell profile
echo 'export PATH="$HOME/.local/bin:$PATH"' >> ~/.bashrc

On macOS with Homebrew, this issue is rare. If it occurs, run brew link semgrep.

Slow scans on large repositories

If scans are taking too long, there are several optimizations:

# Use diff-aware scanning to only check changed files
semgrep ci  # Automatically diff-aware in CI

# Exclude large directories
semgrep --config p/default --exclude "vendor" --exclude "node_modules"

# Limit concurrency to reduce memory usage
semgrep --config p/default --jobs 2

# Skip large files
semgrep --config p/default --max-target-bytes 500000

Out of memory errors

Semgrep can consume significant memory on very large files or complex rule sets:

# Limit maximum memory usage (in MB)
semgrep --config p/default --max-memory 4000

# Reduce the number of rules being run
semgrep --config p/default  # Instead of p/security-audit which has more rules

# Exclude known large files
# Add to .semgrepignore:
# *.min.js
# *.bundle.js
# package-lock.json

Rules not matching expected code

When a custom rule does not match code that you expect it to match:

# Test with verbose output to see what Semgrep is doing
semgrep --config your-rule.yaml --verbose target-file.py

# Use --debug for detailed matching information
semgrep --config your-rule.yaml --debug target-file.py

# Validate your rule syntax
semgrep --validate --config your-rule.yaml

Common reasons rules fail to match:

  • Language mismatch – the languages field in the rule does not include the file’s language
  • Whitespace sensitivity – Semgrep normalizes most whitespace, but multiline patterns need to use ... for gaps
  • Metavariable scope – a metavariable used across patterns must match the same expression in all occurrences

GitHub Actions workflow not triggering

If the Semgrep workflow does not run on pull requests:

  • Verify the workflow file is in .github/workflows/ on the default branch
  • Check that the on: trigger includes pull_request
  • Ensure the YAML syntax is valid – GitHub silently ignores malformed workflow files
  • Check the Actions tab for workflow run errors

SEMGREP_APP_TOKEN errors

If semgrep ci fails with authentication errors:

  • Verify the secret is named exactly SEMGREP_APP_TOKEN in GitHub Settings
  • Ensure the token has not expired in Semgrep Cloud
  • Check that the repository is connected to the correct organization in Semgrep Cloud
  • Regenerate the token in Semgrep Cloud and update the GitHub secret

Findings in generated or vendored code

If Semgrep is flagging code you cannot change:

  1. Add the paths to .semgrepignore
  2. Use inline # nosemgrep comments for individual suppressions
  3. In Semgrep Cloud, triage findings as “Ignored” with a reason of “Generated code” or “Vendored dependency”

Recommended setup for different team sizes

The right Semgrep configuration depends on your team’s size, security maturity, and available bandwidth for triaging findings.

Solo developers and small teams (1-5 developers)

Use Semgrep OSS with the default rule set. Install Semgrep locally, run semgrep --config p/default before pushing code, and add a basic GitHub Actions workflow with p/default. This catches the highest-confidence security issues with minimal noise. Total setup time is about 15 minutes.

# Local development workflow
semgrep --config p/default --error

Mid-size teams (5-20 developers)

Use Semgrep Cloud on the free Team tier. Connect your repositories to Semgrep Cloud, enable PR comments, and start with rules in Comment mode. This gives your team automated feedback on every PR without blocking velocity while you learn which rules are most relevant to your codebase. Promote high-confidence rules to Block mode after a few weeks of triage data. Total setup time is about 30 minutes.

Large teams and enterprises (20+ developers)

Use Semgrep Cloud with a dedicated policy per repository or team. Enable Semgrep Assistant for AI-powered triage to reduce false positive noise. Create custom rules for your internal frameworks and patterns. Integrate SARIF output with GitHub Code Scanning for centralized security visibility. Set up separate policies for different service tiers – stricter rules for payment processing code, lighter rules for internal tools. Total setup time is about 2 hours for the initial configuration plus ongoing refinement.

What to do after setup

Once Semgrep is running in your CI pipeline, the work shifts from configuration to maintenance. Here is a practical sequence for the first 30 days:

Week 1 – Run Semgrep with p/default in Comment mode. Review findings as they come in on PRs. Note any rules that produce frequent false positives in your codebase.

Week 2 – Add paths to .semgrepignore for test files, generated code, and vendored dependencies that are generating noise. Suppress any rule IDs that are consistently false positives for your project.

Week 3 – Promote high-confidence rules to Block mode. Start with rules for critical vulnerabilities like SQL injection, command injection, and hardcoded credentials. Add p/security-audit in Monitor mode to evaluate its findings without surfacing them on PRs.

Week 4 – Write your first custom rule targeting a pattern specific to your codebase – an internal API misuse, a deprecated function that should not be called, or an authentication pattern that must be followed. Share the rule with your team and collect feedback.

This gradual rollout ensures that Semgrep becomes a trusted part of your workflow rather than a noisy tool that developers learn to ignore. The goal is not to enable every rule on day one – it is to build a scanning configuration that your team actually reads and acts on.

Frequently Asked Questions

How do I install Semgrep?

Install Semgrep using pip with ‘pip install semgrep’, using Homebrew on macOS with ‘brew install semgrep’, or using Docker with ‘docker run semgrep/semgrep’. The pip method works on all operating systems and is the recommended approach. After installation, verify it works by running ‘semgrep –version’ in your terminal.

Is Semgrep free to use?

Yes, the Semgrep open-source engine is free under the LGPL-2.1 license and includes 2,800+ community rules. The full Semgrep platform – which adds cross-file analysis, SCA, secrets detection, and AI-powered triage – is free for teams of up to 10 contributors. Beyond 10 contributors, the Team plan costs $35 per contributor per month.

What is the difference between Semgrep OSS and Semgrep Cloud?

Semgrep OSS is the open-source CLI engine that performs single-file pattern matching with 2,800+ community rules. Semgrep Cloud (also called Semgrep AppSec Platform) adds cross-file dataflow analysis, 20,000+ Pro rules, AI-powered triage with Semgrep Assistant, a web dashboard for managing findings, and integrations for PR comments. Semgrep Cloud is free for up to 10 contributors.

How do I set up Semgrep in GitHub Actions?

Create a workflow file at .github/workflows/semgrep.yml that triggers on pull_request and push events. Use the ‘semgrep/semgrep-action@v1’ action or run the Semgrep CLI directly. For Semgrep Cloud integration, add your SEMGREP_APP_TOKEN as a GitHub secret and use ‘semgrep ci’ as the scan command to get PR comments and dashboard reporting.

How do I write custom Semgrep rules?

Create a YAML file with a rules array. Each rule needs an id, a pattern or patterns block, a message, a severity level (ERROR, WARNING, or INFO), and a languages array. Semgrep’s pattern syntax mirrors the target language – you write patterns that look like the code you want to match, using metavariables like $X as placeholders. Test rules with ‘semgrep –config your-rule.yaml’ against your codebase.

What languages does Semgrep support?

Semgrep supports over 30 programming languages including Python, JavaScript, TypeScript, Java, Go, Ruby, C, C++, C#, Rust, Kotlin, Swift, PHP, Scala, Terraform, Dockerfile, and Kubernetes YAML. The open-source engine supports all languages. The Pro engine adds deeper cross-file analysis for a subset of these languages.

How do I reduce false positives in Semgrep?

Use several strategies: create a .semgrepignore file to exclude test files, generated code, and vendor directories. Use Semgrep Assistant (available in the Cloud platform) for AI-powered triage that automatically filters noise. Write custom rules with pattern-not clauses to exclude known-safe patterns. Start with high-confidence rule sets like p/default rather than broad sets like p/security-audit.

What are the best Semgrep rule sets to start with?

Start with p/default, which includes high-confidence security and correctness rules curated by the Semgrep team. Add p/security-audit for broader security coverage when you are ready for more findings. For specific languages, use targeted sets like p/python, p/javascript, or p/golang. For infrastructure scanning, add p/terraform or p/docker-compose. You can combine multiple rule sets in a single scan.

How do I configure Semgrep to post comments on pull requests?

Connect your repository to Semgrep Cloud at semgrep.dev, install the Semgrep GitHub App, and add your SEMGREP_APP_TOKEN to your CI environment. When Semgrep runs with ‘semgrep ci’ in your pipeline, it automatically posts inline comments on pull requests for any new findings. Comments include the rule ID, severity, explanation, and remediation guidance.

Can Semgrep scan Docker containers and infrastructure-as-code?

Yes. Semgrep has dedicated rule sets for Dockerfile security (p/dockerfile), Terraform misconfigurations (p/terraform), Kubernetes YAML (p/kubernetes), and Docker Compose files (p/docker-compose). These rules detect issues like running containers as root, exposing unnecessary ports, missing resource limits, and insecure cloud resource configurations.

How fast is Semgrep compared to other SAST tools?

Semgrep is one of the fastest SAST tools available. The median CI scan time is approximately 10 seconds because Semgrep uses diff-aware scanning to analyze only changed files on pull requests. Full repository scans typically complete in under 60 seconds for most codebases. This is significantly faster than tools like SonarQube, Checkmarx, or Veracode, which often take minutes to hours for comparable analysis.

How do I ignore specific Semgrep findings?

Ignore findings at three levels. In code, add a ‘# nosemgrep: rule-id’ comment on the line before the finding. In configuration, add paths or patterns to a .semgrepignore file. In Semgrep Cloud, triage findings as false positives or accepted risks in the dashboard – these triage decisions persist across future scans so the same finding is not reported again.

Does Semgrep work with GitLab CI and other CI platforms?

Yes. Semgrep works with any CI platform that can run a shell command. For GitLab CI, add a Semgrep job to your .gitlab-ci.yml file. Semgrep also has documented integrations for Jenkins, CircleCI, Buildkite, and Azure Pipelines. The ‘semgrep ci’ command handles authentication, diff-aware scanning, and result reporting regardless of which CI platform you use.

Originally published at aicodereview.cc

Node.js Memory Leaks in Production: Finding and Fixing Them Fast

Node.js Memory Leaks in Production: Finding and Fixing Them Fast

Memory leaks don’t announce themselves. They look like a slow climb on your memory graph, a service that needs a restart every few days, or a gradual latency increase that never quite triggers your alerting threshold. By the time they’re obvious, they’ve already cost you.

This guide covers the most common Node.js memory leak patterns, how to diagnose them using real tools, and how to fix them at the source — not just mask them with a scheduled restart.

What a Node.js Memory Leak Actually Is

JavaScript is garbage collected, so you don’t allocate or free memory manually. A memory leak occurs when objects remain reachable in memory — held by references somewhere in your code — even though you’ll never use them again. The garbage collector can’t collect what it can’t prove is unreachable.

In practice, Node.js leaks happen through three mechanisms:

  1. Global state that grows unbounded (caches, registries, event listeners)
  2. Closures that hold references longer than expected (callbacks, promises, timers)
  3. Third-party library misuse (connection pools not released, streams not destroyed)

Understanding which you’re dealing with changes everything about how you fix it.

Detecting a Leak: The Diagnostic Stack

Step 1: Confirm the leak exists

First, distinguish a leak from legitimate memory growth. A healthy Node.js process will grow memory during request spikes and release it during GC cycles. A leaked process grows and never releases.

Check your production metrics for a sawtooth pattern (healthy) vs. a slow upward trend (leak):

Healthy:       ╭╮  ╭╮  ╭╮  ╭╮   ← memory returns to baseline
Leaking:      ╱  ╲╱  ╲╱  ╲╱   ↑  ← baseline keeps rising

If your process memory grows by >50MB per hour under normal load with no corresponding traffic increase, you have a leak.

Step 2: Add memory monitoring to your app

Add this before you start debugging:

// monitor.js — add to your app startup
const v8 = require('v8');

function logMemoryStats(label = '') {
  const { heapUsed, heapTotal, external, rss } = process.memoryUsage();
  const heap = v8.getHeapStatistics();

  console.log({
    label,
    heapUsed_MB: Math.round(heapUsed / 1024 / 1024),
    heapTotal_MB: Math.round(heapTotal / 1024 / 1024),
    rss_MB: Math.round(rss / 1024 / 1024),
    external_MB: Math.round(external / 1024 / 1024),
    heapSizeLimit_MB: Math.round(heap.heap_size_limit / 1024 / 1024),
  });
}

// Log every 30 seconds
setInterval(() => logMemoryStats('periodic'), 30_000);

// Log on demand via signal
process.on('SIGUSR2', () => logMemoryStats('on-demand'));

Send SIGUSR2 to your process to dump current stats: kill -SIGUSR2 <pid>

Step 3: Take heap snapshots

Heap snapshots are the single most useful tool for finding leaks. They show you exactly what’s in memory and what’s holding references to it.

// heapdump.js — add this endpoint to your Express app (behind auth!)
const v8 = require('v8');
const path = require('path');

app.get('/admin/heapdump', requireAdminAuth, (req, res) => {
  const filename = path.join('/tmp', `heapdump-${Date.now()}.heapsnapshot`);
  const stream = v8.writeHeapSnapshot(filename);
  console.log(`Heap snapshot written to: ${stream}`);
  res.json({ snapshot: stream, message: 'Download from server' });
});

Or trigger from the command line with:

# Node 14+
node --inspect app.js
# Then open chrome://inspect → Memory tab → Take snapshot

The three-snapshot technique:

  1. Take snapshot A after app startup (baseline)
  2. Run your suspected leak scenario 100+ times
  3. Take snapshot B
  4. Run the scenario 100+ more times
  5. Take snapshot C

Open in Chrome DevTools → Memory → Compare A→B and B→C. Objects appearing in both comparisons that you don’t expect are your leak candidates.

The 6 Most Common Node.js Leak Patterns

Pattern 1: Unbounded Caches

The most common Node.js leak. You add a cache to improve performance. You forget a max size. The cache grows forever.

// ❌ This leaks. Every unique userId gets stored forever.
const userCache = new Map();

async function getUser(userId) {
  if (userCache.has(userId)) {
    return userCache.get(userId);
  }
  const user = await db.users.findById(userId);
  userCache.set(userId, user);  // grows without bound
  return user;
}

Fix: Use a bounded cache or WeakMap where appropriate:

// ✅ Option 1: LRU cache with max size
const LRUCache = require('lru-cache');

const userCache = new LRUCache({
  max: 1000,           // max 1000 entries
  ttl: 1000 * 60 * 5, // expire after 5 minutes
});

async function getUser(userId) {
  const cached = userCache.get(userId);
  if (cached) return cached;

  const user = await db.users.findById(userId);
  userCache.set(userId, user);
  return user;
}

// ✅ Option 2: WeakMap for object-keyed caches
// GC can collect entries when the key object is no longer referenced
const requestCache = new WeakMap();

function getCachedForRequest(req) {
  if (!requestCache.has(req)) {
    requestCache.set(req, {});
  }
  return requestCache.get(req);
}

Pattern 2: Event Listener Accumulation

Every call to emitter.on() adds a listener. If you’re doing this inside a function that runs repeatedly, you accumulate listeners without removing old ones.

// ❌ Leaks: a new listener is added on every request
app.get('/stream', (req, res) => {
  emitter.on('data', (chunk) => {  // ← never removed
    res.write(chunk);
  });
});

// Node.js will warn you: MaxListenersExceededWarning
// But it won't stop you

Fix: Always remove listeners when done:

// ✅ Use once() for one-time listeners
app.get('/stream', (req, res) => {
  const handler = (chunk) => {
    res.write(chunk);
  };

  emitter.on('data', handler);

  // Remove when the request ends
  req.on('close', () => {
    emitter.removeListener('data', handler);
  });

  res.on('finish', () => {
    emitter.removeListener('data', handler);
  });
});

// ✅ Or use AbortSignal for automatic cleanup
app.get('/stream', (req, res) => {
  const controller = new AbortController();

  emitter.on('data', (chunk) => {
    res.write(chunk);
  }, { signal: controller.signal });

  req.on('close', () => controller.abort());
});

Audit your listener counts:

// Find emitters with suspiciously many listeners
const EventEmitter = require('events');
const original = EventEmitter.prototype.on;

EventEmitter.prototype.on = function(event, listener) {
  const count = this.listenerCount(event);
  if (count > 10) {
    console.warn(`High listener count: ${count + 1} listeners on '${event}' event`);
    console.trace();
  }
  return original.call(this, event, listener);
};

Pattern 3: Closures Holding Large Objects

Closures capture the entire scope in which they’re defined, not just the variables they use. If a closure references a small variable in a scope that contains a large object, the large object stays in memory.

// ❌ The 'data' array (potentially huge) is captured by the closure
// even though 'processOne' only uses 'item'
function processAll(data) {
  return data.map((item) => {
    return function processOne() {
      // Only uses 'item', but 'data' is still in scope
      return transform(item);
    };
  });
}

Fix: Extract only what you need:

// ✅ Create a separate scope so only 'item' is captured
function processAll(data) {
  return data.map((item) => {
    const copy = { id: item.id, value: item.value }; // copy only what's needed
    return function processOne() {
      return transform(copy);
    };
  });
}

Pattern 4: setInterval / setTimeout Not Cleared

Timers keep their callbacks — and everything those callbacks reference — alive indefinitely.

// ❌ Every call to startPolling creates a timer that's never cleared
function startPolling(connection) {
  setInterval(async () => {
    const results = await connection.query('SELECT * FROM jobs WHERE status = ?', ['pending']);
    results.forEach(process);
  }, 5000);
  // interval is never returned or cleared
}

// Called once per request — creates 1000s of intervals
app.post('/subscribe', (req, res) => {
  startPolling(db);
  res.json({ ok: true });
});

Fix: Always capture and clear timers:

// ✅ Return the timer and clear it when done
class Poller {
  constructor(connection) {
    this.connection = connection;
    this.intervalId = null;
  }

  start() {
    if (this.intervalId) return; // prevent double-start
    this.intervalId = setInterval(() => this.poll(), 5000);
  }

  stop() {
    if (this.intervalId) {
      clearInterval(this.intervalId);
      this.intervalId = null;
    }
  }

  async poll() {
    const results = await this.connection.query(
      'SELECT * FROM jobs WHERE status = ?',
      ['pending']
    );
    results.forEach(process);
  }
}

// Create once, stop when done
const poller = new Poller(db);
poller.start();

process.on('SIGTERM', () => poller.stop());

Pattern 5: Streams Not Properly Destroyed

Readable and writable streams hold buffers and file descriptors. If they’re not destroyed, those resources accumulate.

// ❌ If an error occurs before pipe completes, the stream hangs open
app.get('/file/:name', (req, res) => {
  const readStream = fs.createReadStream(`./files/${req.params.name}`);
  readStream.pipe(res);
  // If 'res' closes early (client disconnects), 'readStream' stays open
});

Fix: Use pipeline which handles cleanup automatically:

const { pipeline } = require('stream/promises');

app.get('/file/:name', async (req, res) => {
  const readStream = fs.createReadStream(`./files/${req.params.name}`);

  try {
    await pipeline(readStream, res);
  } catch (err) {
    // pipeline automatically destroys both streams on error
    if (err.code !== 'ERR_STREAM_PREMATURE_CLOSE') {
      console.error('Stream error:', err);
    }
  }
});

Pattern 6: Connection Pool Exhaustion (Soft Leak)

Not technically a heap leak, but connection pools that grow without releasing connections cause the same symptom: slow resource accumulation that crashes your process.

// ❌ If an error is thrown before release(), the connection is never returned
async function runQuery(sql) {
  const client = await pool.connect();
  const result = await client.query(sql);  // if this throws...
  client.release();  // ...this never runs
  return result;
}

Fix: Use try/finally to guarantee release:

// ✅ Release is always called, even on error
async function runQuery(sql, params = []) {
  const client = await pool.connect();
  try {
    return await client.query(sql, params);
  } finally {
    client.release();  // always runs
  }
}

Automated Memory Leak Detection in CI

Don’t wait for production to find leaks. Add a memory regression test:

// test/memory.test.js
const assert = require('assert');

async function measureMemoryAfterOperations(fn, iterations = 1000) {
  // Warm up
  for (let i = 0; i < 100; i++) await fn();

  // Force GC if available (run Node with --expose-gc)
  if (global.gc) global.gc();

  const before = process.memoryUsage().heapUsed;

  for (let i = 0; i < iterations; i++) await fn();

  if (global.gc) global.gc();

  const after = process.memoryUsage().heapUsed;
  return after - before;
}

describe('Memory regression tests', () => {
  it('getUser() does not grow heap unboundedly', async () => {
    const growth = await measureMemoryAfterOperations(
      () => getUser('user-123'),
      1000
    );

    // Allow up to 5MB growth over 1000 calls
    assert.ok(growth < 5 * 1024 * 1024,
      `Heap grew by ${Math.round(growth / 1024 / 1024)}MB — possible leak`
    );
  });
});

Run tests with node --expose-gc node_modules/.bin/jest to enable manual GC between measurements.

Production Memory Debugging Workflow

When you have a suspected leak in production:

# 1. Get the PID
pgrep -f "node.*app.js"

# 2. Monitor memory over time (watch for upward trend)
watch -n 5 'ps -p <PID> -o pid,rss,vsz --no-headers'

# 3. Take heap snapshot via your /admin/heapdump endpoint
curl -H "Authorization: Bearer $ADMIN_TOKEN" https://your-app.com/admin/heapdump

# 4. Download the snapshot
scp user@server:/tmp/heapdump-*.heapsnapshot ./

# 5. Open in Chrome DevTools
# chrome://inspect → Memory → Load profile → Select your .heapsnapshot file
# Sort by "Retained Size" to see the largest object trees

What to look for in the snapshot:

  • Objects with unexpectedly high retained size
  • Arrays or Maps with thousands of entries that should be small
  • Closure entries (labeled (closure)) pointing to large scopes
  • Event listeners (labeled in (array)) accumulating

The Checklist Before You Ship

Run npx node-deploy-check to automatically scan for:

  • ✅ No setInterval without corresponding clearInterval in cleanup
  • ✅ EventEmitters with setMaxListeners configured
  • ✅ All streams use pipeline or have error handlers
  • ✅ Database queries use try/finally for connection release
  • ✅ Caches have size limits
npx node-deploy-check --check memory

Key Takeaways

  1. The three mechanisms: unbounded state, closure references, third-party misuse. Every Node.js leak is one of these.

  2. Heap snapshots are your friend. The three-snapshot technique (baseline → after N runs → after 2N runs) reliably surfaces accumulating objects.

  3. Monitor continuously. Add process.memoryUsage() logging to every production service. A slow leak caught at +10MB is cheaper than a crash at +2GB.

  4. Test for leaks before production. A 1000-iteration heap test in CI catches 80% of leaks before they ship.

  5. Fix the source, not the symptom. Scheduled restarts hide leaks — they don’t fix them. You will restart more and more frequently as the underlying leak gets worse.

This article is part of the **Node.js in Production* series.*

Run npx node-deploy-check to audit your Node.js project for production readiness — including memory leak risk factors — in under 5 seconds.

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