HTTP Header Checker
Response headers, caching and CDN detection
See every response header a URL returns, with the caching, compression, security and CDN headers called out separately. This is the fastest way to find out why a page is not being cached, or which CDN is in front of a site.
Frequently asked questions
Why is my page not being cached?
Look at Cache-Control. Values like no-store, no-cache or private tell caches not to keep a copy. A missing Cache-Control header is nearly as bad, since caches then have to guess.
Which security headers should I set?
Strict-Transport-Security, Content-Security-Policy, X-Content-Type-Options and Referrer-Policy cover most of the value. This tool flags which of them are present.
How do you detect the CDN?
CDNs add identifying response headers — server names, cache-status headers and request-id headers are all distinctive. We match on those, so a CDN configured to strip them will not be detected.