Create Diagram

Purpose

Produce a correct, rendered diagram from a description, routing each request to the right tool. The deliverable is a verified image plus its source, or, when rendering tooling is genuinely unavailable, validated source clearly labeled as not render-verified. Never deliver diagram code you have not run or validated: unrendered diagram source is the primary failure mode of this skill, because syntax and import errors only surface at render time.

Workflow

Copy this checklist and track progress:

Diagram Progress:
- [ ] 1. Routed by type and destination
- [ ] 2. Matching reference read
- [ ] 3. Content planned
- [ ] 4. Source written, names resolved not guessed
- [ ] 5. Rendered and verified
- [ ] 6. Delivered with source

1. Route by diagram type and destination

Destination overrides type: when the diagram lives inside a Markdown file that GitHub, GitLab, or Obsidian will render (README, docs, vault note), prefer a fenced Mermaid block even for simple architecture, because the destination renders it natively and keeps the source editable in place. Standalone image deliverables prefer the diagrams library for anything infrastructure-shaped, because provider icons carry real information.

2. Read the matching reference

The reference files contain the tool-specific API, syntax, failure modes, and examples. Do not write source from memory of either tool; both have non-obvious traps (import casing in diagrams, reserved words in Mermaid) documented there.

3. Plan the content

List the nodes and relationships before writing source. Keep one diagram to one concern: a diagram that shows the deployment topology, the request flow, and the CI pipeline at once communicates none of them. Offer multiple diagrams instead. Around 15-20 nodes is the practical readability ceiling for a single diagram.

4. Write the source

• diagrams library: never guess an import path or class name. For any node not copied verbatim from the reference's starter list, resolve it first with uv run ${CLAUDE_SKILL_DIR}/scripts/find-node.py <term>; the library has ~2,900 node classes with inconsistent casing, and guessed imports are the top cause of render failure.
• Mermaid: follow the syntax rules in the reference; quote any label containing special characters or reserved words.

5. Render and verify

Mandatory; this is the step that makes the skill reliable.

Python diagrams path:

uv run <filename>.py && ls <filename>.png

Generated scripts include PEP 723 metadata (see the reference) so uv run resolves the diagrams dependency without environment setup. On ImportError, resolve the correct path with uv run ${CLAUDE_SKILL_DIR}/scripts/find-node.py <name> and fix; on ExecutableNotFound: failed to execute 'dot', Graphviz is missing (install per the reference). Re-run until the image file exists.

Mermaid path, in order:

1. If mmdc or npx is available: npx -y @mermaid-js/mermaid-cli -i <file>.mmd -o <file>.svg (first run downloads a headless Chromium; it is slow once, then cached)
2. If neither exists, attempt one install: npm install -g @mermaid-js/mermaid-cli; do not retry on failure
3. If rendering is still unavailable, deliver the fenced source and state explicitly that it was validated but not render-verified
4. Markdown-destination diagrams need no image file; the fenced block is the deliverable, but render locally anyway when tooling exists, because catching a syntax error before commit is the point

Look at the result. After any successful render, open the image with the Read tool and check it: overlapping labels, orphaned nodes, and a layout direction that fights the content are render-success-but-diagram-failure outcomes. Fix and re-render.

6. Deliver

Provide the rendered image and the source file. State what was verified: "rendered and inspected" or "validated, not render-verified, because no renderer was available". Send the image to the user when it is the deliverable.

Universal Rules

• Never deliver source you have not run or validated. Diagram code fails at render time, not at write time; handing over unrun source hands over the debugging.
• Resolve names, never guess them. Applies to diagrams import paths and Mermaid icon or shape names alike.
• No keep-alive processes. Preview servers and watch modes hang agent sessions; render to a file instead.
• One source file per diagram, named for its content (payment-flow.mmd, vpc_topology.py), so re-rendering and editing stay trivial.

Gotchas

• Renaming a class to its "correct" casing breaks it. The diagrams library uses Cronjob, Dynamodb, IOS; the natural-looking CronJob or DynamoDB raises ImportError. The script resolves exact casing; trust its output over instinct.
• Mermaid renders in more places than you think. GitHub, GitLab, and Obsidian all render fenced mermaid blocks natively; an image file is often the wrong deliverable for docs because it cannot be edited or diffed.
• A successful render is not a successful diagram. Graphviz happily renders overlapping edges and unreadable layouts. The inspection step exists because exit code 0 proves syntax, not communication.
• First Mermaid render is slow, not broken. mermaid-cli downloads a headless Chromium on first use; do not abort it or conclude the tool is unavailable mid-download.