Custom Headers - Modify HTTP Headers

🛠️ Modify HTTP headers, redirect URLs & block requests. Provably local MV3 ModHeader alternative — no account, no telemetry.

🛠️ 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. If you’ve been looking for a modern ModHeader alternative or a lightweight Requestly alternative after Manifest V2 was 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 Authorization tokens, custom API keys, X-Forwarded-For values, or CORS headers like Access-Control-Allow-Origin in a click. 🎯 Request and response headers, handled independently. As an HTTP header modifier and header editor, it works in both directions of the connection. 🎚️ 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. Point a staging API at localhost or swap an API version. 🚫 Block requests — stop matching requests from firing at all. Useful for testing failure paths and offline states. 🌍 User agent switcher — override User-Agent per rule, with built-in presets for Windows, macOS, Android, iPhone, iPad, and Googlebot. ⌨️ Keyboard shortcut — toggle every rule 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 Chrome applies your rules — the extension never sees your traffic. It cannot read request or response bodies, because the API gives it no way to. There is no fetch, no webRequest, no account, no telemetry, and no server to call. Your rules live in chrome.storage.local and nowhere else. It’s open source and small enough to read in a minute. Don’t take our word for it — check. 📦 MV3 NATIVE Built from scratch on Chrome Manifest V3. No MV2-style deprecation risk. Works in Chrome, Edge, Brave, Opera, and any Chromium browser. 🚀 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.