HTTP Headers

Why headers matter

Headers help explain how your request traveled across the internet. They can confirm which IP address is exposed to a website and which intermediaries handled your traffic.

They are also useful for troubleshooting access issues, verifying security settings, and understanding how proxies or CDNs are rewriting requests.

Typical use cases

• Verifying VPN or proxy behavior
• Debugging load balancer or CDN routing
• Confirming client IP preservation across hops
• Checking browser and language signals in production

Understanding HTTP Headers

Forwarded IP Headers

When your request passes through proxies, load balancers, or CDNs, various headers may be added to preserve the original client IP address:

• X-Forwarded-For: Contains the original client IP and any intermediate proxy IPs
• X-Real-IP: Often set by reverse proxies to indicate the real client IP
• Forwarded: Standard HTTP header for proxy information (RFC 7239)
• CF-Connecting-IP: Cloudflare-specific header containing the original client IP

Example: an X-Forwarded-For value like 203.0.113.10, 198.51.100.7 indicates the original client followed by a proxy hop, while CF-Connecting-IP may show 203.0.113.10 as the client address seen by Cloudflare.

Other Common Headers

• User-Agent: Identifies your browser, operating system, and device
• Accept-Language: Indicates your preferred languages for content
• Accept: Specifies content types your browser can handle
• Referer: The URL of the page that linked to the current page