Unlimited pages
Separate collections of headers by environment, project or setup. Pages can stay enabled in the background, so you don't have to keep one selected for its headers to apply.
Modify HTTP headers, without the bloat.
A free, lightweight, privacy-focused browser extension for editing request and response headers. Built for my own daily work, now used by thousands of developers.
- 7,000+users
- 4.9 ★Chrome Web Store
- Open sourceMIT licensed
Why it exists
The tools got heavy. This one didn't.
The popular header extensions grew into bloatware: slow, cluttered, and in one case compromised. All most people need is a fast, trustworthy way to set a few headers and get on with their job.
Flex Headers does that and nothing else. No accounts, no tracking, no upsell. It runs entirely in your browser, the source is public, and it has been actively maintained since 2023.
Features
Everything you need, day to day
Smart filters
Scope a page to specific requests with simple URL patterns or full regex, matched against the URL, domain or query string. Excludes always win, so exceptions don't need extra pages.
Import and export
Export one page or all of them to share with your team or back up your setup. Coming from ModHeader? Import its export directly and Flex Headers maps it across.
Cross-device sync
Opt in and your pages, headers and filters follow you between machines via browser sync. A merge-and-tombstone system keeps edits from overwriting each other.
Undo and redo
Step backwards and forwards through edits to headers, filters and pages. Experiment freely and jump back to where you started.
Pause pages
A hard override that switches off every header and filter on a page in one click, without disabling anything individually. Flip it back and everything resumes.
Flexible sorting
Sort headers by name, value or comment, or group enabled headers above disabled ones. Large pages stay readable as your rules grow.
Light and dark
Every screen is designed for both, so it looks right at home in a bright theme or working late.
Chrome and Firefox
Built with WXT so the same extension ships for both browsers, with a Safari app extension in the works.