Modify headers with the header editor
Add request headers, response headers, request cookies, and response cookies in focused tabs.
Modify HTTP Headers and Cookies
An open-source browser extension to modify HTTP request and response headers, inject custom headers and cookies, and test APIs with switchable local profiles. Available for Chrome, Firefox, and Edge.
Built for debugging
Open-source browser extension to modify headers and cookies.
Header Override keeps the workflow deliberately narrow: add a rule, choose request or response behavior, scope it where needed, and let the extension apply it. Profiles keep separate projects tidy when one browser needs several debugging setups.
Use the Header Override extension in Chrome, Edge, and Firefox to modify headers with local rules for API debugging, staging checks, and QA workflows.
Request and response headers
Feature set
Features
Scope header rules by URL
Scope matching rules with browser-supported URL filter patterns.
Modify request and response cookies
Set response cookie Domain, Path, SameSite, Lifetime, Max-Age, and Secure attributes.
Use header editor profiles
Keep up to five local rule profiles for different projects, accounts, or test setups.
Import and export header rules
Move selected profiles between browsers with local JSON import and export.
Chrome, Edge, and Firefox support
Use Header Override in Chrome, Edge, and Firefox.
Organize and toggle header rules
Enable, disable, delete, and annotate rules with comments.
Keep header rules stored locally
Rules are saved locally in your browser and never sent to a server.
Real extension UI
A fast way to switch a test setup.
The profile dropdown and header rules are shown from actual extension captures, with the same popup layout users see in the browser.
ModHeader alternative
Open-source ModHeader alternative for local header and cookie overrides.
Header Override is open source and keeps rules in local browser storage, making it a lightweight alternative to ModHeader for scoped request headers, response headers, and cookies. Compare Header Override as a ModHeader alternative.
Common uses
When a local rule would answer the question faster.
- Send debug headers to staging APIs without touching application code.
- Reproduce customer-specific headers or cookies with scoped local rules.
- Toggle backend flags while testing UI flows in your browser.
- Switch between client, environment, or test-account setups with profiles.
- Document temporary QA rules before removing them.
FAQ
Answers for searchers and reviewers.
What is Header Override used for?
Header Override helps developers, QA teams, and support engineers modify HTTP headers and cookies from the browser for scoped debugging and testing workflows.
Is Header Override an alternative to ModHeader?
Yes. Header Override is an open-source, lightweight ModHeader alternative for modifying request headers, response headers, request cookies, and response cookies with local browser rules.
Are rules sent to a server?
No. Rules are stored locally in browser extension storage and are used only to apply the header or cookie changes you configure.
Can rules target specific URLs?
Yes. Header and cookie rules can be scoped with browser-supported URL filter patterns, so changes apply only to matching requests.
Why does Header Override request access to websites?
Header Override needs access to all URLs because you can create rules for any website and scope them with URL filters. Request header and cookie values are sent only to destinations matching your URL filters; response values are applied only to matching responses. No rule data or browsing activity is transmitted to the developer or developer-controlled servers.
Local by design
No analytics. No tracking. No external servers.
Rules are saved in your browser's local extension storage and used only to apply the header and cookie changes you configure. Request values are sent only to matching destinations, while response values are applied only to matching responses. No rule data or browsing activity is transmitted to the developer or developer-controlled servers.