Render PlantUML diagrams natively on GitHub.com. This extension detects plantuml code blocks on any GitHub page (READMEs, issues, pull requests, discussions, wikis) and renders them inline as SVG diagrams, exactly the way GitHub already renders Mermaid. No server. No tokens. No tracking. Zero permissions. The entire PlantUML engine runs client-side inside a sandboxed iframe shipped with the extension. Nothing is sent to a remote server, no API keys are required, and the extension declares zero host permissions, no storage access, and no tabs API access. It only runs on github.com. Features

Renders all standard PlantUML diagrams: sequence, class, component, deployment, state, use-case, activity, object, timing, and more.
Also recognizes the puml and wsd language aliases.
Each rendered block has a small header bar with a toggle button that switches between the diagram and the original PlantUML source (using GitHub's own syntax highlighting).
Follows GitHub's light/dark color mode automatically.
Works on issues, PRs, discussions, READMEs, wikis, and gists.

How it works The TeaVM-compiled PlantUML engine is bundled with the extension and runs entirely inside a sandboxed iframe with an opaque origin — no network access, no shared state with the host page. The same architecture GitHub itself uses for Mermaid. Open source MIT-licensed. Source code and issue tracker: https://github.com/plantuml/plantuml-for-github

PlantUML

Published Firefox add-on:

PlantUML for GitHub