HeaderTweaker

Easilymodify outgoing HTTP headers

Tweak headers globally or for specific URLs so you never send more than intended. No shenanigans, all local, free & open source. Forever.

Add to FirefoxAdd to Chrome
  • No tracking
  • No telemetry
  • No remote code
  • MIT licensed
The HeaderTweaker popup: three headers targeted to headertweaker.com and a global X-Debug header, each with an on/off toggle
01 / FEATURES

For developers, testers, designers and/or power‑users

Whether you need to communicate with APIs that require authentication tokens, run A/B tests, simulate different browsers or debug CORS issues, this lightweight extension gives you full control over the outgoing headers without touching server code.

The Edit header panel with key, value, optional label and a list of target URLs
Header details

Update header details when you need to

Every header gets a key, a value and an optional label. Leave it global, or scope it to as many target URLs as you need — including the page you’re on right now.

The Bulk URL target change dialog, step 1: three of four headers selected
Bulk URL targets

Change the URL targets for several headers at once

Prevent your headers from being applied to every request you make by targeting multiple headers at once to specific URLs.

The Global tab showing one header with a notice that global headers apply to all requests
All · Global · Current

Filter the header-list to see what applies where

Switch between All, Global and Current. Headers that apply everywhere are flagged, so it’s clear what’s reaching sites you probably didn’t mean to target.

The Settings panel with the master switch, a Use labels toggle and Import and Export buttons
Settings

Export, import or pause your configuration

Export your headers to a JSON file to move them to another browser or share them with your team. A single switch pauses every rule without deleting any of them.

02 / HOW IT WORKS

Set it up once, then browse as usual

  1. 1

    Add a header

    Enter a key and a value, and optionally a label so you remember why it’s there.

  2. 2

    Set a target

    Leave it global, or target it to a specific URL.

  3. 3

    Browse as usual

    Matching requests leave your browser with the headers applied. Whenever you’re done toggle it off or remove it completely.

03 / PRIVACY

All your base are belong to you

HeaderTweaker asks for the smallest set of permissions and collects no data whatsoever. Configuration only leaves the browser when you export it yourself. Period.

  • No tracking, telemetry or analytics
  • Stored locally with the browser’s storage API
  • No remote code — only what ships in the package runs
PermissionWhy it’s needed
storageFirefox & ChromeKeeps your header rules and settings locally in the browser.
webRequest + webRequestBlockingFirefoxModifies outgoing request headers before they’re sent.
declarativeNetRequestWithHostAccessChromeLets Chrome apply the rules without the extension reading request contents.
<all_urls>Firefox & ChromeLets rules target any site. Rules only run on requests that match your URL targets — except localhost, which every rule always matches.
04 / CROSS-BROWSER

Built on each browser’s native API

One codebase, using whichever API each browser exposes for modifying requests.

API usedHow it works
FirefoxwebRequestHeaders are modified on outgoing requests before they’re sent.
ChromedeclarativeNetRequestThe browser applies the rules itself — the extension never reads or intercepts your requests.

Install HeaderTweaker

Free, open source and MIT licensed.

Add to FirefoxAdd to Chrome