HeaderTweaker

HeaderTweaker is a browser extension for adding and changing outgoing HTTP request headers. Create header rules, enable or disable them, delete the ones you no longer need, and optionally scope them to specific URL targets.

Features

• Add, edit, enable, disable, and delete header rules — each with a key, value, and optional label.
• Scope a rule to specific URL targets, or leave it global; change the targets of several rules at once.
• Filter the rule list by All, Global, or Current; global rules are flagged so it's clear what reaches every site.
• Import and export configuration as JSON.
• Pause every rule at once from the settings panel without deleting them.
• Firefox support through webRequest and Chrome support through declarativeNetRequestWithHostAccess.

All configuration is stored locally in the browser.

Permissions & Privacy

HeaderTweaker requests the smallest possible set of browser permissions and collects no data whatsoever.

Firefox

Permission	Purpose
storage	Persist header rules and settings locally in the browser.
webRequest + webRequestBlocking	Modify outgoing request headers before they are sent (Firefox uses the webRequest API).
<all_urls>	Allow rules to target any site. Rules only run on requests matching the URL targets defined in the extension (localhost is always matched, regardless of a rule's configured URL targets).

Chrome

Permission	Purpose
storage	Persist header rules and settings locally in the browser.
declarativeNetRequestWithHostAccess	Modify outgoing request headers via Chrome's declarativeNetRequest API, which changes requests without the extension reading their contents.
<all_urls> (host access)	Allow rules to target any site. declarativeNetRequestWithHostAccess only acts on hosts that have been granted access.

On Chrome, HeaderTweaker deliberately uses declarativeNetRequestWithHostAccess instead of the broader declarativeNetRequest permission. The declarative approach lets the browser apply rules without the extension inspecting or intercepting request contents.

Note: localhost requests (localhost, *.localhost, 127.0.0.1, [::1]) always receive matching header rules, even if a rule's URL targets don't include localhost. This override applies on both Firefox and Chrome.

Privacy commitments

• No tracking, no telemetry, no analytics. The extension contains no tracking scripts and makes no outbound calls.
• No data collection or transmission. Header rules never leave the device. All configuration is stored locally via the browser's storage API.
• No remote code. Only the code shipped in the package is executed.

Import and export are fully manual: configuration leaves the browser only when it is explicitly exported to a JSON file.

License

MIT

Monorepo setup

• apps/browser-extension — the Firefox/Chrome browser extension
• apps/website — website (headertweaker.com), built with Astro
• packages/icons — shared icons used by both
• packages/tokens — shared SCSS design tokens used by both

Getting started

pnpm install
pnpm build:all         # Build the extension for Firefox and Chrome
pnpm dev:website       # Run the website locally