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HTTP Header Checker
Read the raw response headers a server sends.
About the HTTP Header Checker
Headers decide how a page is cached, whether it is indexed, how it is compressed and how the browser treats it. They are also invisible unless you go looking, which is why misconfigurations survive for years.
Look first at X-Robots-Tag. A stray noindex here overrides anything in the HTML and removes the page from search results without leaving a trace in the source anyone would think to check. Then look at Cache-Control: a static asset with no caching headers is downloaded again on every visit, and an HTML page cached for a week will serve stale content to returning visitors.
The security headers are listed too. They do not affect rankings, but X-Content-Type-Options, Referrer-Policy and a sensible Strict-Transport-Security value cost nothing and close off a category of problems.
Common questions
Why would a page be deindexed with no visible change to the content?
A stray X-Robots-Tag: noindex header overrides anything written in the HTML and removes the page from search results without changing a single visible word — this tool is often how people finally find it.
What's a healthy Cache-Control setting for a static asset?
Something like public, max-age=31536000, immutable for a CSS or JS file that has a version number in its filename, so browsers can cache it for a year safely.
Do the security headers affect SEO?
Not directly, but a sensible Strict-Transport-Security, X-Content-Type-Options and Referrer-Policy cost nothing to add and close off a category of vulnerabilities.