HTTP Header Explainer
Free online HTTP header explainer. Search and browse all standard HTTP headers grouped by category. Each header includes a description, syntax, example values, and whether it is a request or response header. All processing happens in your browser.
About This Tool
HTTP headers are key-value pairs sent between a client and server as part of every HTTP request and response. They carry essential metadata about the connection, the content being transferred, authentication credentials, caching rules, and security policies. Understanding HTTP headers is fundamental for web developers, API designers, and anyone working with network communication.
Headers are grouped into several categories. General headers like Cache-Control and Connection apply to both requests and responses. Request headers such as Accept, Authorization, Host, and User-Agent are sent by the client to provide context about what it needs and who it is. Response headers like Location, Set-Cookie, and Server provide information from the server back to the client. Representation headers including Content-Type, Content-Length, and Content-Encoding describe the format and encoding of the message body.
Security headers play a critical role in protecting web applications. Content-Security-Policy prevents cross-site scripting (XSS) and data injection attacks. Strict-Transport-Security enforces HTTPS connections. CORS headers (Access-Control-Allow-Origin, etc.) control which origins can access resources across domains. X-Frame-Options prevents clickjacking by controlling whether a page can be framed.
Caching headers like Expires, Last-Modified, ETag, and Vary work together with Cache-Control to determine how responses are cached by browsers and intermediary proxies. Proper caching configuration significantly improves performance and reduces server load.
This tool provides a searchable, categorized reference of all standard HTTP headers. You can filter by direction (request, response, or both) and search by header name, description, or example value. Each entry shows the header syntax and a real-world example you can copy with one click.
Frequently Asked Questions
What are HTTP headers?
HTTP headers are key-value pairs sent between clients and servers in HTTP requests and responses. They carry metadata such as content type, authentication credentials, caching directives, and security policies. Every web request includes headers that help the client and server communicate effectively.
How do I use the HTTP Header Explainer?
Browse headers by category (General, Request, Response, Representation, Security, Caching) or use the search bar to find a specific header by name. You can also filter by direction to show only request headers, response headers, or both. Click Copy to copy an example header value to your clipboard.
Is this tool free and is my data safe?
Yes, the HTTP Header Explainer is completely free to use. All data is processed entirely in your browser — nothing is sent to any server. There is no sign-up required.
What is the difference between request and response headers?
Request headers are sent by the client (browser) to the server, providing information like accepted content types, authentication credentials, and cookies. Response headers are sent by the server back to the client, providing information like content type, caching rules, and set cookies. Some headers like Cache-Control can appear in both.
Which HTTP headers are most important for security?
The most important security headers include Content-Security-Policy (prevents XSS), Strict-Transport-Security (enforces HTTPS), X-Content-Type-Options (prevents MIME sniffing), X-Frame-Options (prevents clickjacking), and Referrer-Policy (controls referrer information). CORS headers (Access-Control-Allow-Origin, etc.) are also critical for API security.
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HTTP Header Explainer
Free online HTTP header explainer. Search and browse all standard HTTP headers grouped by category. Each header includes a description, syntax, example values, and whether it is a request or response header. All processing happens in your browser.