ModHeader V3 by ModHeader Inc.

ModHeader by modheader.app is a powerful Firefox Add-on for modifying, adding, editing, removing, and overriding HTTP request headers and HTTP response headers. Whether you're a web developer, frontend engineer, backend developer, QA tester, DevOps engineer, security researcher, API developer, or IT professional, ModHeader provides an easy way to inspect and customize network requests directly from your browser.

Modify headers without changing your application code. Instantly override User-Agent, Referer, Origin, Cookie, Authorization, Accept, Accept-Language, Cache-Control, Host, X-Forwarded-For, X-Requested-With, Content-Type, Content-Length, Connection, DNT, Sec-Fetch headers, custom headers, and many more.

• Modify HTTP request headers
• Modify HTTP response headers
• Add new request headers
• Add new response headers
• Edit existing headers
• Remove unwanted headers
• Override request headers
• Override response headers
• Replace header values
• Disable headers
• Enable headers with one click
• Create reusable header profiles
• Switch between profiles instantly
• Apply rules based on URL patterns
• Enable or disable rules per website
• Import and export configurations
• Backup and restore profiles
• Lightweight and fast
• Privacy focused
• No unnecessary permissions

ModHeader is built for modern web development and API testing.

Use ModHeader to:

• Test REST APIs
• Test GraphQL APIs
• Debug HTTP requests
• Debug HTTP responses
• Simulate different browsers
• Change User-Agent strings
• Override Referer headers
• Modify Origin headers
• Edit Authorization tokens
• Inject Bearer tokens
• Test JWT authentication
• Add API keys
• Modify cookies
• Test CORS behavior
• Debug CORS issues
• Test CDN configurations
• Test reverse proxies
• Test load balancers
• Test cache behavior
• Test localization using Accept-Language
• Test mobile websites
• Test desktop websites
• Test browser compatibility
• Simulate different devices
• Simulate crawlers and bots
• Debug authentication flows
• Test staging environments
• Test production APIs safely

• HTTP header editor
• Request header modifier
• Response header modifier
• Header manager
• User-Agent switcher
• Referer changer
• Cookie editor
• Origin modifier
• Authorization header editor
• API testing tool
• REST API testing
• GraphQL testing
• Network debugging
• Web development
• Frontend development
• Backend development
• Website debugging
• Browser debugging
• CORS testing
• Security testing
• Penetration testing
• QA automation
• Software testing
• Web application testing

• User-Agent
• Referer
• Origin
• Cookie
• Authorization
• Accept
• Accept-Encoding
• Accept-Language
• Cache-Control
• Pragma
• Connection
• Upgrade-Insecure-Requests
• DNT
• Host
• Content-Type
• Content-Length
• X-Requested-With
• X-Forwarded-For
• X-Real-IP
• X-API-Key
• Custom headers
• Response headers
• Request headers

• Clean and intuitive interface
• Fast rule matching
• Easy profile management
• Reliable request interception
• Powerful header modification engine
• Designed for developers
• Works with modern websites
• Regular updates
• High performance
• Easy to learn
• Advanced features for professionals

Whether you're debugging an API, testing authentication, modifying request headers, overriding response headers, changing User-Agent, editing cookies, troubleshooting CORS, or building modern web applications, ModHeader by modheader.app is the Firefox Add-on that helps you work faster and more efficiently.