Finally a structured approach to system design: arc-agent.
It is a Go CLI for turning a system design prompt into a real design workspace: requirements, entities, APIs, high-level design, optional deep dives, and architecture diagrams.
The core idea is simple: do not ask an agent for one big architecture document and hope it is coherent. Split the work into stages, validate every artifact, repair failures, and render the result into files that are easy to review.
What it produces
An arc-agent workspace contains structured YAML artifacts plus generated outputs:
arc.yaml
01-requirements.yaml
02-entities.yaml
03-api.yaml
04-high-level-design.yaml
06-diagram.yaml
DESIGN.md
diagram.mmd
diagram.excalidraw.png
That gives you a readable design doc, Mermaid source, and image artifacts without losing the structured intermediate data.
Quickstart
Install the CLI:
curl -fsSL https://raw.githubusercontent.com/ariel-frischer/arc-agent/main/install.sh | sh
Then ask it for a design:
arc-agent new "Design a URL shortener like Bitly" --out designs/bitly
arc-agent inspect designs/bitly
arc-agent validate designs/bitly
arc-agent render designs/bitly --format all
You can run it through an agent provider such as OpenCode, Codex, or Claude Code. You can also use direct mode with OpenCode Go structured outputs when you want stricter, faster generation.