CDN & Cache Header Guide

About the CDN & Cache Header Guide

Explains how to identify the CDN serving a website from its HTTP response headers, with the tell-tale header for each major provider. (Browser security prevents reading another site's headers directly, so this is a reference guide.)

How to use

Pick a provider to see the header signature, or enter a header value to identify it.

Worked example

A 'cf-ray' header means the site is behind Cloudflare.

How to use this calculator

1. Open the page you want to check and inspect its response headers.
2. Look for CDN-related header names such as server, x-cache, via, x-served-by, cf-ray, x-amz-cf-pop, x-cache-hits, or age.
3. Match the header patterns to the CDN or edge network that set them.
4. Use the headers together, not just one field, to confirm the provider.

Step by step method

1. Check the response headers from the site request in your browser dev tools, a curl command, or this guide's output.
2. Identify any CDN-specific markers, such as Cloudflare, Fastly, Akamai, CloudFront, or another edge platform.
3. Compare multiple headers to separate the origin server from the CDN layer.
4. Use the combination of headers and cache behavior to decide which CDN is serving the site.

Worked example

Suppose you inspect a website and see several response headers that point to an edge cache provider.

1. You find headers including cf-ray, server: cloudflare, and age: 124.
2. The cf-ray header is a strong Cloudflare indicator, and the server value confirms it.
3. The age header shows the cached response has been served from the CDN cache.

Tips and common mistakes

• Do not rely on the server header alone, because it can be hidden or changed.
• Look for a cluster of CDN clues, not one isolated header.
• Remember that some sites use multiple layers, so the visible CDN may be the outer edge network.
• If headers are missing or generic, try a request from curl with full header output.

Frequently asked questions