Mod Header

Add, change, or remove HTTP request & response headers. Scope each rule by request URL and by the site making the request.

Mod Header is a fast, no-frills tool for adding, changing, or removing HTTP request and response headers — built for web developers and QA. What you can do • Set, append, or remove any request or response header • Group multiple headers into a "config" with individual on/off toggles • Collapse configs to keep a long list tidy • "Request URL" filter — target where the request goes (its destination) • "Only on sites" filter — apply a config only to requests made FROM a given site (e.g. your localhost dev app), so other sites stay untouched • Header name/value suggestions from your history (remove any entry inline) • Toggle configs individually, or flip the master switch to pause everything • Everything is saved locally and takes effect instantly Popular uses • Spoof the Origin header for local development against a dev/staging API • Add an Authorization or custom header to API calls while testing • Override CORS response headers (e.g. Access-Control-Allow-Origin) locally Privacy All rules are stored locally in your browser and never leave your device. No accounts, no tracking, no servers.