Custom Headers - Modify HTTP Headers

🛠️ Custom Headers is a free, MV3-native Chrome extension for developers, QA testers, and API integrators who need to modify HTTP headers, redirect requests, and block URLs — without handing their browsing to a cloud service. Looking for something to replace ModHeader or Requestly now that Manifest V2 is retired? This extension is built to fill that gap. ⚡ WHAT YOU CAN DO 🔧 Modify HTTP headers — add, replace, append, or remove any request or response header on any site. Set an Authorization token, an API key, X-Forwarded-For, or Access-Control-Allow-Origin in a click. 🎚️ Scope every rule — apply it to all URLs, to a URL pattern, or to a regular expression. Keep staging tokens away from production. 🔀 Redirect rules — send any matching URL somewhere else, with regex capture groups supported. Send staging calls to localhost or swap an API version. 🚫 Block requests — stop anything that matches from firing at all. Useful for testing failure paths and offline states. 🌍 User agent switcher — override User-Agent on the sites you choose, with built-in presets for common desktop and mobile browsers and a search engine crawler. ⌨️ Keyboard shortcut — switch everything on or off without leaving the keyboard. 🌐 Export and import — your whole rule set is a plain JSON file. Share it with teammates, commit it to a repo, or move it between machines. 🔒 PROVABLY LOCAL This is the part that matters. Custom Headers is built on declarativeNetRequest, which means the browser applies your changes itself and your traffic never passes through us. It has no way to read the body of anything you send or receive. There is no fetch, no webRequest, no account, no telemetry, and no server to call. Everything you set up stays in chrome.storage.local and nowhere else. Don’t take our word for it — check. Turn on Developer mode in chrome://extensions, inspect the extension’s service worker, and watch its Network tab stay empty. 📦 MV3 NATIVE Built from scratch on Manifest V3, with no MV2-style deprecation risk. Works in Chrome and other Chromium-based browsers. 🚀 GET STARTED Install, open the popup, add your first header rule. No signup, no email, works offline. ⚠️ WHAT IT DOESN’T DO Custom Headers cannot inspect or rewrite request bodies, mock API responses, or throttle your connection — declarativeNetRequest doesn’t allow it, and that limitation is exactly what makes the privacy guarantee real. If you need a full traffic debugger, use Chrome DevTools.