Header Override is a small browser extension for overriding request headers, response headers, request cookies, and response cookies with configurable local rules.

• Chrome Web Store: https://chromewebstore.google.com/detail/gkobmjeklkiepibofnghbkcjiphjacfm

• Microsoft Edge Add-ons: https://microsoftedge.microsoft.com/addons/detail/albhpnnccbkfkloddpaecdmhpnmnldhn

• Firefox Add-ons: https://addons.mozilla.org/en-US/firefox/addon/headeroverride

• Website: https://headeroverride.com

extension/      Browser extension manifests, icons, and modular source
  src/shared/   Pure rules, profiles, storage schema, and DNR compilation
  src/platform/ Browser API adapters
  src/background/ Background synchronization and badge entry point
  src/popup/    Popup state, persistence, profile transfer, and views
tests/unit/     Fast tests for pure model and state modules
tests/e2e/      Playwright browser-extension tests
assets/         Store and product assets
docs/           Publishing notes and privacy policy source
scripts/        Release packaging and screenshot helpers
dist/           Ignored local release packages

The public website is maintained in a separate repository so this repository can stay focused on the browser extension.

1. Run npm run build.
2. Open your browser's extensions page.
3. Enable Developer mode.
4. Click Load unpacked.
5. Select the extension/ folder.

The generated extension/build/ directory contains browser-compatible bundles and is intentionally ignored by Git. Edit files under extension/src/, then rebuild.

Open the extension popup, choose a tab, and add a rule:

• Request Headers and Response Headers override HTTP headers for matching URL filters.
• Request Cookies overrides outgoing Cookie headers.
• Response Cookies overrides response Set-Cookie headers.
• URL filter is used for header and cookie rules with declarative request-rule matching syntax. |http* matches HTTP and HTTPS requests.
• Comment is an optional note for labeling or documenting a rule.

Rules are saved automatically and synced into the browser's dynamic request rules.

Use Node.js 22.12 or newer, then install dependencies:

npm ci

Run the end-to-end test suite:

npm run test:e2e

Run the end-to-end tests in Playwright debug mode:

npm run test:e2e -- --debug

Run the unit and end-to-end suites together:

npm test

Tests run in headed mode by default. To run them headlessly, pass --headless:

npm run test:e2e -- --headless

Run the suite against the latest available Chrome for Testing Stable, Beta, or Dev:

npm run test:e2e:stable
npm run test:e2e:beta
npm run test:e2e:dev

Pass --headless after -- to run any channel without a visible browser, for example npm run test:e2e:stable -- --headless.

Each command builds the extension, resolves the latest available version for the selected channel, downloads it into .cache/browsers if needed, and runs Playwright with that executable. The version and executable path are printed before the tests. An internet connection is needed to resolve the channel on each run; existing downloads are reused. These tests open a visible browser, like the default suite. Chrome for Testing supports the unpacked-extension flags used by this harness.

The latest Stable, Beta, and Dev versions are resolved from Chrome for Testing's last-known-good-versions.json metadata. Browser archives are then downloaded from Google's public storage using the pattern https://storage.googleapis.com/chrome-for-testing-public/<version>/<platform>/chrome-<platform>.zip and extracted into .cache/browsers/chrome/<platform>-<version>.

Pass Playwright arguments after --, for example:

npm run test:e2e:beta -- tests/e2e/theme.spec.ts
npm run test:e2e:dev -- --grep "request header overrides"

To reuse a specific downloaded browser without resolving or downloading a channel:

E2E_BROWSER_EXECUTABLE="/absolute/path/to/chrome" npm run test:e2e

E2E_BROWSER_EXECUTABLE takes precedence over E2E_BROWSER_CHANNEL. The default npm run test:e2e command continues to use Playwright's bundled browser when both variables are unset.

Create release packages for Chrome, Edge, and Firefox:

npm run package:extension

Create a package for one browser:

npm run package:extension:chrome
npm run package:extension:edge
npm run package:extension:firefox

Packages are written to the ignored dist/ directory.

Generate screenshots and promotional assets from the real extension UI:

npm run screenshots:generated

Header Override's source code is licensed under the MIT License.

The Header Override name, logo, and branding assets in extension/icons/ are not licensed under the MIT License. All rights to those branding elements are reserved.