PlantUML for GitHub от PlantUML

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