Show HN: Arrowproof – check an LLM-drawn architecture diagram against your code

Every arrow in your architecture diagram, checked against the code.

Karpathy's advice is to ask your LLM for a diagram instead of a wall of text. The advice is good, with one catch: a diagram that a model draws looks right even when it is wrong. arrowproof is an agent skill that checks every box and every arrow of an Excalidraw diagram against the real import graph of your repository. It shows you the import line behind each arrow.

The result: 15 arrows verified. 1 arrow is indirect, because app.py reaches config.py only through sansio/app.py. 2 arrows have no import behind them, because views.py imports only globals.py and the type aliases in typing.py. 1 box points to blueprint.py, a file that does not exist (the real file is blueprints.py). Claude Opus drew the same architecture with 20 arrows, and all 20 passed. Both runs are in examples/flask.

Try it live, with nothing to install:

• The Flask architecture as a step-by-step explainer , with the import lines behind every arrow.

• The evidence report for the Haiku diagram . Click an arrow to see why it passed or failed.

• The checked Haiku diagram in Excalidraw , ready to edit.

• Checks every arrow.A → B claims that code in box A imports code in box B. The result is ✓ verified, ↝ indirect (through one other file), ⇄ reversed, or ✗ not in code.

• Checks every box. The path must exist. A package must be imported somewhere.

• Finds what the diagram leaves out. It lists the imports between two boxes that have no arrow.

• Shows the receipts. The HTML report shows the file, the line and the import statement behind each arrow. Click an arrow to see them.

• Draws new diagrams. It lays out a short spec as an editable.excalidraw file, then checks it.

• Explains a change, step by step. An interactive page walks through the checked diagram. Each step zooms to its boxes and shows the import lines behind its arrows. Arrows without evidence stay marked, so the story cannot claim more than the code shows.

• Runs in CI. The exit code is 1 when a diagram in your docs no longer matches the code.

It reads Python and JavaScript/TypeScript: tsconfig paths, workspace packages, require and import(). It uses the Python standard library only. There is nothing to install.

For any agent that reads Agent Skills (Claude Code, Codex, Cursor, Gemini CLI, OpenCode and others):

npx skills add ahmtsahin/arrowproof

As a Claude Code plugin:

claude plugin marketplace add ahmtsahin/arrowproof
claude plugin install arrowproof@arrowproof

Then ask your agent:

• "Draw the architecture of this repo."
• "Check docs/architecture.excalidraw against the code."
• "Is this diagram still correct?"

python skills/arrowproof/scripts/graph.py .
python skills/arrowproof/scripts/verify.py docs/architecture.excalidraw --repo .

graph.py prints the real import graph, grouped by file or folder. verify.py accepts an .excalidraw file or a spec, and writes <name>.verified.excalidraw and <name>.report.html. The original file does not change.

A spec is a short JSON file:

{"title": "Checkout service",
 "nodes": [{"id": "web", "label": "Browser"},
           {"id": "api", "label": "HTTP API", "paths": ["src/api"]},
           {"id": "orders", "label": "Orders", "paths": ["src/orders"]},
           {"id": "pg", "label": "Postgres", "packages": ["pg"]}],
 "edges": [{"from": "web", "to": "api", "kind": "flow"},
           {"from": "api", "to": "orders"},
           {"from": "orders", "to": "pg", "label": "queries"}]}

Karpathy's next step after the diagram is an interactive page. explain.py turns a checked diagram into one: the diagram on the left, a guided tour on the right, and the code behind every arrow.

python skills/arrowproof/scripts/explain.py architecture.spec.json --repo .

Add a tour to the spec to tell the story in your own words, step by step. Without one, the tour is built from the verified arrows alone, with at most 4 arrows on a step. Either way, the page ends with what the code does not support and what the diagram leaves out. Each step plays for 6 to 14 seconds, by the length of its text, and a button switches between 1×, 1.5× and 2×. A link can open a step, a speed and autoplay: #step=3&speed=2&play=1.

Try it live: Flask, drawn by Claude Opus and arrowproof's own architecture.

- uses: actions/checkout@v4
- run: git clone --depth 1 https://github.com/ahmtsahin/arrowproof /tmp/arrowproof
- run: python /tmp/arrowproof/skills/arrowproof/scripts/verify.py docs/architecture.excalidraw --repo . --no-report

This repository does the same for its own diagram, examples/self, on every push.

A box maps to code through customData.arrowproof on the Excalidraw element: {"paths": ["src/api"]} or {"packages": ["stripe"]}. A diagram from arrowproof already carries this data. A diagram that someone drew by hand is mapped by its labels: a path in the label, or the name of a file, a folder or a package. The report tells you which boxes were mapped by label, so that you can correct a wrong match.

An arrow can carry a kind. uses is the default and is checked in the direction of the arrow. flow is a data or request flow, for example an HTTP call or a child process. An import in either direction confirms a flow. Without one, the flow stays unchecked, because a run-time flow is not visible in the imports. skip is a conceptual arrow and is not checked. An arrow from a package to your code is checked in either direction, because a package cannot import your code.

A package box counts as present when a file imports the package or when package.json, requirements*.txt or pyproject.toml declares it. A box whose files are in a language that arrowproof does not read leaves its arrows unchecked instead of marking them wrong.

• The check reads imports only. HTTP calls, queues, dependency injection and imports with computed names are not visible. A ✗ is a claim without evidence, not proof of a bug.
• An import under TYPE_CHECKING orimport type supports an arrow but is marked as type-only. It does not count for indirect paths or for missing arrows.
• Only Python and JavaScript/TypeScript are read. Hidden folders such as .tmp or.runtime are skipped, except.github ,.claude ,.claude-plugin ,.codex ,.agents and.storybook , and any hidden folder that a box names.
• The SVG preview approximates the Excalidraw look. Open the .excalidraw file in excalidraw.com, VS Code or Obsidian for the real one.

python -m unittest discover -s tests

tools/render-check.html opens a file with the official Excalidraw library, to confirm that it loads and to make the images in docs/. Serve the repository root (for example python -m http.server 8765) and open tools/render-check.html?file=../examples/flask/haiku.verified.excalidraw.

tools/record_gif.py records an explainer page as the GIF in docs/. It needs Google Chrome and Pillow:

python tools/record_gif.py "http://localhost:8765/examples/flask/opus.explainer.html#play=1&speed=2" docs/explainer.gif

MIT