A Chrome (Manifest V3) extension that highlights .diff and .patch files in the browser: additions green, deletions red, with hunk/file headers styled and the underlying code syntax-highlighted by language. Works on GitHub/Bitbucket PR .diff/.patch URLs, raw files, and local file:// diffs. Light/dark aware, fast, and fully toggleable.

How it works

A content script runs only on text/plain pages whose URL ends in .diff/.patch (the include_globs matcher covers query strings too, e.g. …/123.diff?token=…).
It reads the browser-rendered <pre>, parses the unified-diff structure, and:
1. Instantly repaints every line with its diff color (green/red/context/headers).
2. Progressively layers syntax highlighting via highlight.js, processed in idle-time chunks so large diffs stay responsive. Above ~50k highlightable lines, syntax is skipped to preserve speed (diff colors remain).
Toggling is instant and reload-free: the popup writes chrome.storage.sync, and the content script re-renders on change. Alt+D flips the master toggle from anywhere.
Only the storage permission is requested — declarative content scripts need no host permissions.

Toggles

Control	Effect
Highlighting (popup)	Master switch for the green/red diff layer.
Syntax highlighting (popup)	Layer language-aware token colors on top.
`Alt+D`	Flip the master switch (rebind at `chrome://extensions/shortcuts`).

Build

Requires Node 20+.

npm ci
npm run build      # type-checks, then bundles to dist/
npm run watch      # rebuild on change (dev)

dist/ is the unpacked extension (git-ignored).

Load in Chrome

chrome://extensions → enable Developer mode.
Load unpacked → select the dist/ folder.
For local diffs, open the extension's Details page and enable “Allow access to file URLs.” Then try samples/example.diff.

Continuous integration (Codeberg / Forgejo Actions)

CI lives in .forgejo/workflows/ci.yml and runs npm ci → typecheck → build in a node:22-bookworm container — the same steps as a local build, so a green local build means green CI.

To wire it up on Codeberg:

Push this repo to Codeberg:

git remote add origin https://codeberg.org/<you>/diff-highlighter.git
git push -u origin main

Connect a runner: repo Settings → Actions → Runners (or use Codeberg's hosted runners). If using a hosted runner, change runs-on: docker to its label (e.g. codeberg-tiny).

Scope

Triggers on URLs/files whose path ends in .diff/.patch and that render as plain text. In-app HTML diff views (GitHub's "Files changed", Bitbucket's /diff endpoint) are out of scope — those are full HTML pages, not raw text.

Layout

src/
  manifest.json      MV3 manifest
  content.ts         detect + render + live toggle
  diff-parser.ts     pure diff parsing / language detection
  background.ts      defaults + Alt+D command
  popup/             popup UI
  styles/            diff.css, hljs-theme.css, popup.css (all light/dark)
scripts/             build.mjs (esbuild), make-icons.mjs
.forgejo/workflows/  CI