PlantUML for GitHub, from PlantUML, is a Firefox extension that embeds PlantUML diagram previews into GitHub pages for documentation and review workflows. It renders PlantUML source in-place using a browser-side engine so contributors do not need to export images manually. The extension supports GitHub themes, offers a source/diagram toggle, and targets software architects, developers, and technical writers who require quick, private diagram previews inside repository interfaces.

How it changes documentation and review flows

The extension removes the manual export step from documentation workflows by rendering diagrams inline, which speeds visual verification during code review and writing. It operates across most repository interfaces, including additional surfaces such as discussions and Gists, and mimics GitHub's own sandboxing pattern for embedded diagrams so rendered content sits visually alongside Markdown without an external viewer.

What diagram syntaxes and formats it recognises

Support covers standard PlantUML diagram types and aliases, so sequence, class, and activity diagrams render from their native text. The extension accepts language aliases such as 'puml' and 'wsd' and preserves the original source in a toggleable view that shows the text with GitHub's native syntax highlighting, which helps reviewers inspect or copy the underlying model directly.

How it handles privacy, permissions, and performance

Rendering is designed to avoid external servers and tracking, using a zero-tracking, zero-server architecture and a zero-permission philosophy that minimizes required browser access. The extension runs locally in the page context and is also compatible with Chromium-based browsers where the same approach applies. Local rendering yields immediate diagrams in situ, a behaviour reported as fast in community feedback.

A practical choice for individual contributors and privacy-minded teams

PlantUML for GitHub is a pragmatic tool for developers and documentation authors who want fast, in-repository previews without sending diagram data to third-party services, a point reflected by positive ratings on the Firefox Add-ons store. It is less suitable for teams that require centralized, server-side image pipelines or repository-hosted image assets. For reviewers, enable the extension during walkthroughs to shorten visual checks.