HeaderSmith — Modify HTTP Request & Response Headers

A simple MV3 alternative to ModHeader. Add, edit & remove HTTP request & response headers by URL. Import your ModHeader rules.

HeaderSmith is a lightweight, MV3-native way to add, edit, and remove HTTP request AND response headers on any site — a simple alternative to ModHeader. Already using ModHeader? Import your existing rules from a ModHeader JSON export in one step and keep working. WHAT YOU CAN DO • Modify both request and response headers — not just requests. • Three operations per header: set, append, or remove. • Target rules by URL pattern (use * to match every site, or scope a rule to one host). • Flip any rule on or off instantly with a per-rule toggle — no need to delete and recreate. • Import your ModHeader rules from a JSON export. BUILT ON THE MODERN CHROME API HeaderSmith uses Chrome's declarativeNetRequest (Manifest V3). It does not intercept your traffic through a background listener and does not read the contents of the requests it modifies — Chrome applies your header rules directly. PRIVACY BY DEFAULT • No analytics. No tracking. No ads. • Your header rules are stored locally in your browser (chrome.storage) — HeaderSmith never collects or transmits them. • The only network request HeaderSmith makes is to its payment provider (ExtPay) to verify your license status. That's it — no analytics, no tracking, and your rules and browsing data are never part of it. A SAFETY NET If a rule would attach a header to EVERY site you visit, HeaderSmith warns you before enabling it — so you don't accidentally leak an auth token to third parties. Scope the rule to the host you need and you're covered. PRICING • Free: up to 5 active rules. • Pro: unlimited rules. Great for API development and testing, adding auth or custom headers to specific hosts, overriding CORS or cache headers during local work, and reproducing request/response conditions across environments.