Headmaster — HTTP Header Editor

Send extra request headers to matching URLs — no profiles, every rule independent.

Headmaster is a simple, private way to modify HTTP request headers — add, edit, or remove them per site, with no profiles. Add custom request headers, override existing values, or remove headers on the URLs you choose. Other header editors lock you into a single "active profile," so sending the same header with different values across environments is awkward. Headmaster drops that model — every rule is independent and always evaluated, so you can send: • X-Env: dev to dev.example.com • X-Env: staging to staging.example.com • X-Env: prod to example.com …all at once, with no switching. Features • Independent rules — the same header name can have different values per URL • Set, append, or remove request headers • Simple URL matching using Chrome's declarativeNetRequest patterns • See at a glance how many rules apply to the current tab • Per-rule enable/disable, plus a master enable-all / disable-all toggle • Duplicate rules in one click • A quick popup and a full-page manager (whichever you prefer) • Export and import your rules as JSON for backup or sharing Private and trustworthy • Open source (MIT): https://github.com/mattmorganpdx/headmaster • Zero runtime dependencies — nothing is loaded from the network • Collects no data; your rules stay on your device • Uses Chrome's declarativeNetRequest, so it never reads your requests or responses • Requests access to a site only when you add a rule for it How it works Each rule compiles to one Chrome declarativeNetRequest rule with its own URL filter. Chrome evaluates them all per request, so matching rules apply together — no active-profile gate.