View all HTTP headers sent by your browser with our free HTTP headers viewer tool. This header checker shows request headers, user agent information, cookies, referrer data, and other metadata transmitted with every web request. Perfect for debugging, testing APIs, verifying proxy configurations, and understanding what information your browser sends to websites.
HTTP headers are metadata fields sent with every web request and response. When your browser requests a webpage, it sends headers containing information about your browser, device, preferred language, cookies, and more. Understanding these headers helps diagnose issues, verify configurations, and see exactly what information websites receive about you.
Identifies your browser, version, and operating system. Websites use this to serve optimized content for different devices and browsers. Format typically includes browser name, version, rendering engine, and platform information.
Tells the server what content types your browser can handle (HTML, JSON, images, etc.). The server uses this to send the appropriate format. Multiple types can be listed with quality values indicating preferences.
Indicates your preferred languages for receiving content. Websites use this for automatic localization. Lists languages in order of preference with optional quality values.
Specifies compression methods your browser supports (gzip, deflate, br). Servers use this to compress responses, reducing bandwidth usage and improving load times.
Contains cookies previously set by the website. Used for session management, authentication, tracking, and storing user preferences. Shows all cookies being sent to the current domain.
The URL of the previous page that linked to the current request. Websites use this for analytics and security checks. Note the misspelling is part of the HTTP specification.
Contains credentials for HTTP authentication. Used by APIs and secured resources. Common formats include Basic, Bearer (for tokens), and various custom authentication schemes.
Directives for caching mechanisms. Controls whether and how responses should be cached by browsers and intermediary servers. Values like "no-cache" prevent caching, while "max-age" specifies cache duration.
When requests pass through proxies, load balancers, or CDNs, additional headers appear:
HTTP headers reveal information about your system and browsing context:
Privacy-focused browsers and extensions can modify or remove headers to reduce fingerprinting and tracking. VPNs and proxies may add headers showing the request was forwarded.
This HTTP header viewer makes a request to our server, which echoes back all headers it receives from your browser. This shows exactly what information websites see when you visit them. The tool displays both common headers in an easy-to-read format and a complete table of all headers for technical analysis.
If API requests fail with authentication errors, check if the Authorization header is present and correctly formatted. Verify tokens haven't expired and are being sent with each request.
When sending data to APIs, ensure the Content-Type header matches your data format (application/json for JSON, application/x-www-form-urlencoded for forms). Mismatches cause parsing errors.
Cross-Origin Resource Sharing problems often relate to Origin headers and Access-Control headers. Check that requests include the correct Origin and that servers respond with appropriate Access-Control-Allow headers.
If you're seeing outdated content, examine Cache-Control headers. Use "no-cache" or "no-store" to prevent caching during development. Check If-None-Match and If-Modified-Since headers for conditional requests.
Many applications add custom headers for specific purposes:
Custom headers typically start with "X-" by convention, though modern standards prefer using standard headers or defining new ones properly. View these headers to verify they're being sent correctly by your application.
Yes, all headers sent by your browser are visible to the receiving web server. This is fundamental to how HTTP works. However, most websites only log and use a subset of headers relevant to their operation.
Browser extensions like ModHeader or Requestly allow modifying headers for testing purposes. Developers can set custom headers using JavaScript fetch API or XMLHttpRequest. Command-line tools like curl provide complete header control.
Some headers are only sent in specific contexts. For example, Authorization headers appear only when credentials are configured, Cookie headers only when cookies exist for that domain, and Referer only when navigating from another page.
When using HTTPS, all headers are encrypted during transmission. However, proxies and intermediaries can see headers at each hop. Use HTTPS for sensitive headers like Authorization tokens to prevent interception.
Request headers are sent from your browser to the server (shown by this tool). Response headers come from the server back to your browser. Both contain different types of information - requests describe your capabilities and preferences, responses describe the content being delivered.