Headerbench

Headerbench is a browser extension for developers that sets, appends and removes HTTP request and response headers on the sites you choose. It also handles redirects, blocks and CORS / Content-Security-Policy presets.

• Profiles per environment (local, staging, production), several active at once with a clear priority order
• Filters by domain, URL pattern, regex, request type and method
• Works on fetch, XHR, POST, iframes and images through Chrome's declarativeNetRequest engine
• "Test a URL" shows which rules apply and why
• Imports profiles exported from ModHeader, exports to JSON
• Asks for no site access at install; access is requested per profile and can be revoked
• No account, no analytics, no remote code; unminified, source available on GitHub: https://github.com/Darkhouse13/headerbench

Free features have no rule limits. Pro ($36/year or $79 once) adds mock API responses, regex redirects, shared variables and sync.

Not affiliated with ModHeader.