Last updated: 2026-09-03

GitHub Mermaid JSDoc Viewer is a browser extension that finds ```mermaid fenced code blocks (inside JSDoc comments in JS/TS files, or as plain fences in Markdown files) on the GitHub page you are viewing, and shows a small badge next to the line number that lets you preview the diagram or open it in the Mermaid Live editor.


The extension does not collect, store, sell, or share any data. There is no backend server, no analytics, no telemetry, no crash reporting, and no account.

• It runs only on https://github.com pages. Because GitHub navigates client-side (Turbo), the script has to be present on every github.com page, but it stays idle everywhere except on source files (/blob/), pull requests (/pull/), commits (/commit/) and branch comparisons (/compare/).
• Scanning happens entirely locally: the extension reads the source lines already rendered on the page you are viewing and looks for mermaid fences. Nothing is sent anywhere at this stage.
• No GitHub login, token or API is used. The extension works the same on public and private repositories because it only reads what your browser has already displayed.

The extension itself has no server. To render a diagram it relies on two public services run by the Mermaid project, and it only contacts them after an explicit click by you:

| When you… | What is sent | Where |
| -------------------------------- | -------------------------------------------------------------------- | ----------------------------------------- |
| Click a 📊 / 🔀 badge | The text of that mermaid diagram (and, for 🔀, its previous version) | https://mermaid.ink (renders an SVG) |
| Click Open in Mermaid Live ↗ | The text of that mermaid diagram | https://mermaid.live (opens the editor) |

The diagram text is compressed and embedded in the URL (the standard pako: format used by the Mermaid Live editor). No other content of the page, file, repository or diff is sent — only the lines between the ```mermaid and ``` fences you clicked. Your GitHub identity, the repository name and the file path are not transmitted.

If the diagram comes from a private repository, be aware that its text will be processed by mermaid.ink / mermaid.live when you click. Their handling of that data is governed by the Mermaid project's own terms: <https://mermaid.js.org/> . If you do not want a diagram to leave your browser, simply do not click its badge — the extension never sends anything on its own.


None. The extension uses no localStorage, sessionStorage, cookies, IndexedDB or extension storage.


The extension requests no permissions. The toolbar popup learns whether the current page is supported by messaging the content script, not by reading the tab's URL.

| Access | Why it is needed |
| ---------------------------------------- | --------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- |
| Content script on https://github.com/* | Needed on all github.com pages because GitHub navigates client-side without reloading; it reads the code already rendered on file, PR, commit and compare pages to find mermaid fences, and overlays the badge and the preview modal. No other site is touched. |


The extension bundles one open-source library, pako (MIT license), used locally to compress the diagram text into the pako: URL format. It is copied unmodified from the official npm package (see PAKO_LICENSE). No remote code is loaded or executed.


Changes to this policy are tracked in the project's Git history. Questions: open an issue at <https://github.com/g-ongenae/github-mermaid-jsdoc-viewer/issues>.