HeaderModifier

Free tool to add, override, and remove HTTP request/response headers with profiles and URL filters.

HeaderModifier is a free, privacy-friendly tool for developers and testers who need to change HTTP headers. Add a header, override an existing one, or remove it entirely — then scope it to exactly the sites you choose. Built on Chrome's modern Manifest V3 declarativeNetRequest engine, HeaderModifier modifies headers efficiently at the network layer, with no external servers and no background tracking. ✦ Features • Modify request headers — add new ones or override existing values • Modify response headers — add or override • Remove headers — just leave the value empty • Profiles — keep multiple independent header sets and switch between them instantly • Per-header toggles — enable or disable individual headers with one click • Per-header comments — annotate any header so you remember what it's for • URL filters — apply headers only to certain domains, or exclude specific domains • Import / export — back up or share your configuration as a JSON file • Active-header badge — see at a glance how many headers are live ✦ Private by design • No accounts and no sign-up • No tracking, no analytics, no ads • Your configuration is stored locally and never leaves your device • 100% free and open source (MIT licensed) ✦ Common uses • Add an Authorization or custom API header while testing • Override User-Agent, Accept-Language, or Referer • Remove headers to reproduce edge cases • Simulate different environments with separate profiles ✦ Good to know When you add a custom request header to a cross-origin API call, the browser performs a CORS preflight, and the server must allow your header via its Access-Control-Allow-Headers response for it to be accepted. This is standard browser behavior and applies to every header tool.