DevHeader — Header Injector & HTTP Header Editor

Add & edit HTTP request and response headers per site. Fix CORS, set profiles, paste-to-add. No sign-up, no paywall.

DevHeader is the fastest way to add and edit custom HTTP headers in your browser. Built for developers, QA, and anyone testing APIs, feature flags, A/B tests, or staging environments — without the clutter or paywalls. 🔁 Request AND response headers Edit request headers (Authorization, User-Agent, custom x- headers) and response headers with one tap. Fix CORS errors by adding Access-Control-Allow-Origin, tweak Content-Security-Policy, override Cache-Control, and more. ⚡ Add your headers in seconds Paste "x-env: staging" and it's added instantly — no clicking through forms. Paste a whole block of headers at once and DevHeader splits them for you. 🎯 Profiles that just work One profile is active at a time — pick it and it applies immediately. Search and switch between profiles even when you have dozens. Spin up a profile per project, environment, or teammate. Duplicate, rename, delete in one tap. 🌍 Scope to the sites you want Target localhost, a specific domain (subdomains included), or * for everything. New profiles default to * so you're ready to go. 🟢 See what's live at a glance A green dot and master switch tell you exactly when headers are being injected. Flip the switch off and everything stops — no guessing. 🎨 A UI you'll actually enjoy Warm, modern, and automatically matches your browser's light or dark theme. 🔒 Private by design • No sign-up, no account, no cloud. • No analytics, no tracking, no remote code. • Everything stays in your browser's local storage. • Open source and fully inspectable. 💸 Free. All of it. Every feature — profiles, import/export, unlimited headers — is free. Forever. Great for: • Testing staging / preprod with custom routing headers • Overriding Authorization, User-Agent, Accept-Language • Feature flags and A/B test bucketing (x-ab-testing, x-feature-branch) • Debug headers for SSR / edge / CDN • API development and QA Import & export your profiles as JSON to share with your team or move between machines. How it works: DevHeader uses Chrome's official declarativeNetRequest API to modify the initial navigation request, fetch/XHR calls, assets, and WebSocket handshakes. It does not run content scripts and makes no network calls of its own. Server-to-server requests made by your SSR backend must forward headers themselves.