Will your Mermaid diagrams render, read and cite on GitHub?
Paste a Markdown document with Mermaid diagrams. Your browser checks it against the markdown-mermaid-writing style guides - accessibility titles, theme directives, node ids, labels, headings, footnotes - and applies the safe fixes, free and without uploading anything. A paid run then reviews it, fixes it (re-linted here before you take it), or drafts a diagram from a prose passage.
Each example has a saved model run, so you can see the whole page for free.
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What this does, and what it does not
The standard is the one the agent skill
markdown-mermaid-writing
sets for documentation: Markdown with Mermaid as the source of truth, every diagram
accessible and theme-neutral, every external claim cited. The lint is this page's reading of
the skill's two style guides, written rule by rule from their wording - it is not Mermaid's
own parser and it does not render your diagrams. It catches the traps the guides name (an
end node id, a bare radar keyword, emoji in sankey or architecture
labels) and structural gaps such as an unclosed subgraph, but a diagram can pass the lint
and still fail in Mermaid for reasons the guides do not cover. Heuristic rules - title case,
long labels, ids that do not match labels - are notes, not warnings, and the review may
dispute them.
The paid run reads your document and the findings and must answer every one of them. A fixed document is linted again here and compared with yours before you take it, including every URL, so an invented source shows up; nothing is written back to your repository. A drafted diagram is linted on its own and its labels are checked against the passage it came from. The style guides are Apache-2.0, by Clayton Young / Superior Byte Works LLC, carried in the skill under the MIT licence of k-dense-ai/scientific-agent-skills - see the notice. The two example documents are fictional and written for this page. Diagram Lint is an independent tool; it is not affiliated with or endorsed by Mermaid Chart Inc. or the Mermaid project. Mermaid is named here only as the diagram syntax it checks.