HeaderMod - HTTP Header Modifier

Effortlessly add, modify, and remove HTTP request and response headers for API testing, CORS debugging, and development.

HeaderMod - HTTP Header Modifier & Mock Utility Take complete control over your HTTP request and response headers directly from your browser. HeaderMod is a modern, ultra-fast Manifest V3 developer tool designed for web developers, QA engineers, API architects, and security testers. Whether you need to test authentication tokens, mock response headers, bypass cross-origin resource sharing (CORS) restrictions in local development, spoof User-Agent strings, or debug complex API endpoints, HeaderMod gives you an intuitive, lightning-fast workflow. ================================================== KEY HIGHLIGHTS & CAPABILITIES ================================================== 🚀 Manifest V3 Native Engine Built from the ground up using Chrome's native DeclarativeNetRequest API. Enjoy zero latency, near-zero CPU and memory usage, and instant rule application without page lag or browser restarts. 🔄 Full Request & Response Header Modification • Add, overwrite (SET), append, or strip (REMOVE) any HTTP request header. • Add or modify HTTP response headers (e.g., Access-Control-Allow-Origin, Content-Security-Policy, X-Frame-Options) to unblock local testing. • Fine-grained control over individual headers with one-click enable/disable switches. 🎯 URL Scoping & Wildcard Filtering Apply custom headers globally across all domains (*), or target specific staging environments, microservices, or localhost ports (e.g., *localhost:3000*, *api.staging.example.com*). Supports both profile-level and per-rule URL filters. 📂 Multi-Profile Management Create isolated profiles for different projects and environments (e.g., "Local Development", "Staging QA", "Production Debug", "Mobile Emulation"). Switch profiles instantly with a single click. ⚡ Instant 1-Click Presets • Bypass Local CORS: Injects wildcard Access-Control-Allow-Origin, Methods, and Headers for cross-origin development. • Bearer Token Authentication: Pre-configured Authorization header for quick JWT and API token injection. • Mobile User-Agent Spoofing: Emulate modern iPhone/Safari devices to test responsive layouts and server-side device detection. • Force Cache Bypass: Sets Cache-Control: no-cache, no-store and Pragma: no-cache to guarantee fresh asset loading. • JSON REST Headers: Quickly sets Content-Type and Accept headers to application/json. 🔒 Privacy First & 100% Offline Your data never leaves your computer. HeaderMod contains zero analytics, zero trackers, and zero external network calls. All configurations and headers are stored exclusively in your browser's local storage. 💾 Backup, Import & Export Easily export your profiles to clean JSON files to backup your rules or share them with teammates for seamless onboarding and reproducible testing environments.