Validate WebExtensions manifest (and optionally permissions/APIs) against MDN browser-compat-data

browser-extension-compat-data

MDN WebExtensions compatibility data (manifest fields, APIs, and permissions) in one lean package. Query whether a feature is supported in a browser/version (lookup), lint a whole extension across multiple targets (validate), or wire it into ESLint.

• Data: MDN browser-compat-data (webextensions)
• No runtime fetch. Ships a single compact JSON asset (~24 KiB gzipped), not the full ~15 MB MDN dataset.

Install

npm i browser-extension-compat-data

Lookup: "is this supported?"

import {
  isSupported,
  getSupport,
  getMinVersion,
  getMdnUrl,
} from 'browser-extension-compat-data'

isSupported('api', 'runtime.sendMessage', 'safari') // => true
isSupported('manifest', 'side_panel', 'firefox') // => false
isSupported('api', 'scripting.executeScript', 'chrome', '88') // version-gated

getMinVersion('manifest', 'action', 'chrome') // => "88"
getMdnUrl('permissions', 'tabs') // MDN url (explicit or derived)

getSupport('api', 'runtime.sendMessage')
// { chrome: { supported: true, versionAdded: "26" }, safari: { supported: true, ... }, ... }

First arg is the domain ('manifest' | 'api' | 'permissions'), second the dotted BCD key. An unknown browser throws (a typo can never read as a silent pass); the canonical set is in BROWSERS.

Validate a whole extension, across targets

import { analyzeExtension } from 'browser-extension-compat-data'

const report = await analyzeExtension('./my-extension', [
  { browser: 'chrome', version: '116' },
  { browser: 'firefox', version: '115' },
  { browser: 'safari', version: '16.4' },
])

report.ok // false if any target has findings
report.scannedFiles // sources resolved from the manifest (background, content scripts)
for (const { target, findings } of report.targets) {
  // findings: { kind, key, reason, browser, message?, file?, loc?, mdnUrl?, support? }
}

It reads manifest.json, checks every field/permission MDN knows about (including host_permissions and optional_permissions), applies Manifest V2/V3 structural rules, and scans referenced source for chrome.*/browser.* usage. That scan includes scripts inside HTML entry-points (popup, options, devtools, sidebar, new-tab overrides), both external <script src> and inline blocks.

Usage resolution follows destructuring, webextension-polyfill imports, and aliasing, with file:line:column on every finding.

reason is one of not-supported | removed | partial | flag | manifest-version | no-compat-data.

Lower-level validators

import {
  getUnsupportedManifestFields,
  getUnsupportedAPIsFromFile,
} from 'browser-extension-compat-data'

await getUnsupportedManifestFields('./manifest.json', {
  browser: 'safari',
  version: '17',
})
await getUnsupportedAPIsFromFile('./background.js', {
  browser: 'firefox',
  scanMode: 'accurate',
})

scanMode: 'accurate' (default for analyzeExtension) parses the AST and is alias-aware; 'fast' is a quick regex heuristic.

CLI

npx browser-extension-compat-data ./my-extension --targets chrome116,firefox115,safari16.4

manifest: ./my-extension/manifest.json
scanned 2 source file(s): bg.js, content.js

✓ chrome 116: no issues
✗ firefox 115: 3 issue(s)
    [not supported] manifest: side_panel
    [not supported] api: offscreen.createDocument (bg.js:3:0)
    [no compat data] permission: offscreen

Exits non-zero when anything is reported. --scan all scans every script in the directory; --mode fast; --no-permissions; --json.

ESLint plugin

// eslint.config.js
import { eslintPlugin } from 'browser-extension-compat-data'

export default [
  {
    plugins: { 'webext-compat': eslintPlugin },
    rules: {
      'webext-compat/compat': [
        'warn',
        { targets: ['firefox115', 'safari16.4'] },
      ],
    },
  },
]

Flags chrome.*/browser.* calls unsupported by your targets, inline in the editor. It is alias-aware (destructuring, webextension-polyfill, aliasing), the same resolution the analyzer uses.

Typed keys

The generated key unions ship with the package, so consumers can opt into compile-time safety:

import type {
  ApiKey,
  ManifestKey,
  PermissionKey,
} from 'browser-extension-compat-data'

const used = ['runtime.sendMessage', 'tabs.query'] satisfies ApiKey[] // typo => compile error

The runtime functions accept any string (so dynamic keys and custom datasets still work); the unions are opt-in.

API surface

type Domain = 'manifest' | 'api' | 'permissions'
type Browser = 'chrome' | 'edge' | 'firefox' | 'firefox_android' | 'opera' | 'safari' | 'safari_ios'

// Lookup
isSupported(domain, key, browser, version?) // throws on unknown browser
getSupport(domain, key) / getBrowserSupport(domain, key, browser)
getMinVersion(domain, key, browser) / getMdnUrl(domain, key) / hasFeature(domain, key) / listKeys(domain)

// Validate
analyzeExtension(input, targets, options?) -> ExtensionReport
getUnsupportedManifestFields(path, options) / getUnsupportedAPIsFromFile(path, options)
evaluateManifest(manifestObject, browser, version?, checkPermissions?)

// Browsers / targets / helpers
BROWSERS, isKnownBrowser, assertBrowser, parseTarget, parseTargets
compareVersions, buildMdnUrl, runCli, eslintPlugin

// Data source (tests / custom datasets)
getIndex, setIndex, setIndexFromFile, resetIndex

Data & provenance

The package ships one precomputed file, src/generated/index.json, copied to dist/index.json at build time and read lazily (not inlined into the bundles). It flattens MDN's webextensions/{manifest,api,permissions} into key -> { u?: mdnUrl, s: { browser: { a, r?, p?, f? } } } (a version_added, r version_removed, p partial, f behind-a-flag). getIndex().v reports the upstream BCD version.

A daily GitHub Action re-syncs MDN BCD, rebuilds the index + src/generated/keys.ts, and commits only when the data changed.

# rebuild locally against a checkout of mdn/browser-compat-data
node scripts/build-index.mjs path/to/browser-compat-data/webextensions src/generated/index.json

Node-only at runtime (reads the JSON asset via fs).

Related projects

• browser-extension-manifest-fields
• browser-extension-capabilities
• extension-from-store
• chrome-extension-manifest-json-schema
• parse5-asset-patcher

License

MIT (c) Cezar Augusto.