Header Editor Pro – Modify HTTP Headers by Charly Brown

Header Editor Pro is a free, open source HTTP header editor for developers. Add, modify or remove request and response headers, with no account, no telemetry and no limits.

What it does

• Request and response headers — set or append, each one individually toggleable
• Unlimited profiles — no three-profile ceiling
• Domain filters — scope a profile to the domains you choose, so staging headers never reach production
• Pause everything with one click, without losing your configuration
• Reorder headers by dragging them
• Import and export profiles as JSON
• 7 languages: English, Español, 日本語, 한국어, Русский, 简体中文, 繁體中文

Typical uses

• API testing — send Authorization: Bearer <token> to authenticated endpoints
• CORS debugging — add Access-Control-Allow-Origin to reproduce and diagnose
• Environment switching — X-Environment: staging against a different backend
• Device testing — change User-Agent to compare mobile and desktop responses

Privacy

No data collection, no analytics, no telemetry, no external servers. Your configurations live in local browser storage and never leave your machine. Header rules are applied by the browser itself through the declarativeNetRequest API — the extension does not read page content, and never sees the requests it modifies.

The full source is on GitHub under the MIT licence. Read it, audit it, fork it.

Free, and nobody pays for it

No paywall, no "pro" tier, no nag screens. Nobody funds this work. If you want something improved, open an issue on GitHub and let's talk it through.

Source code: https://github.com/testacode/header-editor-pro-free