# extension-js/extension.js

The cross-browser extension framework.

Repository: https://github.com/extension-js/extension.js
Canonical: https://ross.abutalabs.com/products/extensionjs
Homepage: https://extension.js.org
Language: TypeScript
License: MIT
License Family: permissive
Topics: webextension, browser-extension, cli, chrome-extension, cross-browser, edge-extension, manifest-v3, playwright, preact, react, scaffold, starter-template, svelte, typescript, vue, zero-config, safari-web-extension, extension-js, firefox-extension, content-script
Last push: 2026-08-24T10:16:00+00:00

## Health v2 (maintenance only)
Score: 95/100 (v2, computed 2026-09-03T02:39:23.370411+00:00)
- activity 99, release rhythm 87, longevity 100
- inputs: {"age_days": 2141, "days_push": 9, "days_rel": 11, "gap_med": 0, "n_releases_24m": 108}
- flags: none
- formula: round(0.45*activity + 0.35*rhythm + 0.20*longevity); archived -> min(score, 10)

## Adoption (not part of the score)
Stars 5069, forks 131 (observed 2026-08-28T04:09:09.299618+00:00)

## What it is
Extension.js is a zero-config framework and CLI for building cross-browser extensions for Chrome, Edge, Firefox, and Safari from a single codebase. It handles manifest compilation with browser-prefixed fields, hot module replacement for extension scripts, per-browser build outputs, and store-ready packaging.

## Use cases
- build a chrome extension with react and typescript
- ship one extension to chrome edge and firefox from a single codebase
- scaffold a browser extension project from a template
- get hot reload for content scripts and background service workers
- package an extension as a zip for the chrome web store
- run a github extension sample without cloning or configuring
- handle manifest v3 differences between chromium and firefox

## When to choose
- you want zero build configuration for a new browser extension
- you need to target multiple browsers from one manifest.json
- you want HMR for popup, options, content, and background scripts
- you prefer first-class TypeScript, React, Vue, Svelte, or Preact support
- you want to prototype by running GitHub extension samples directly

## When to avoid
- you need an all-in-one platform with store publishing and updates built in
- your project is already deeply invested in another bundler like webpack or Vite plugins
- you need to support browsers or engines outside the Chromium and Gecko families
- your environment cannot run Node.js 22.12 or newer

## Facets
- artifact type: framework
- maturity: active
- function: build-tool, cli, browser-extension, developer-tools, scheduling
- domain: browser-extensions, web-development, developer-tools, cross-platform
- platform: browser, browser-extension, cli, cross-platform
- tags: manifest-v3, hot-module-replacement, zero-config, webextension, chrome-extension, firefox-extension, safari-web-extension, scaffolding, typescript, react, vue, svelte, preact, cross-browser, nodejs

## Member repositories
- extension-js/extension.js (main) score 95

## Provenance
- Observed fields: from GitHub, fetched 2026-08-28T04:09:09.299618+00:00.
- Health v2: computed from the inputs above; adoption is never an input.
- Inferred fields (summary, facets, guidance): AI-extracted, prompt v1, taxonomy v1, on 2026-08-29T18:02:49.646170+00:00, confidence not recorded.
  - readme: https://github.com/extension-js/extension.js (fetched 2026-08-28T04:09:09.299618+00:00, sha 59af279a3bd0)
  - homepage: https://extension.js.org (fetched 2026-08-29T08:58:04.437800+00:00, sha a97234523067)
  - site_page: https://extension.js.org/docs (fetched 2026-08-29T08:58:04.441105+00:00, sha c0765367093d)
  - site_page: https://extension.js.org/docs/getting-started/templates (fetched 2026-08-29T08:58:04.443334+00:00, sha 922ebaca3ea8)
  - site_page: https://extension.js.org/docs/ai-access (fetched 2026-08-29T08:58:04.445380+00:00, sha add27b29f786)
  - site_page: https://extension.js.org/docs/getting-started/immediately (fetched 2026-08-29T08:58:04.447314+00:00, sha b906a9980451)
  - site_page: https://extension.js.org/docs/features/browser-specific-fields (fetched 2026-08-29T08:58:04.449298+00:00, sha a220c1c9781c)
  - site_page: https://extension.js.org/docs/getting-started (fetched 2026-08-29T08:58:04.451335+00:00, sha 470eb0318504)
  - site_page: https://extension.js.org/docs/features/cross-browser-compatibility (fetched 2026-08-29T08:58:04.453900+00:00, sha 877f888ea374)
  - site_page: https://extension.js.org/docs/implementation-guide/manifest-json (fetched 2026-08-29T08:58:04.456117+00:00, sha 2535938d5d11)
- Data as of 2026-08-30T08:39:29.467469+00:00.