Performance Tools
Cache Headers Checker
Analyze a website's caching headers - Cache-Control, Expires, ETag, Last-Modified, and Age.
Enter a domain to analyze its caching headers.
JustChecker tracks your website's performance signals continuously.
Frequently Asked Questions
Cache-Control is the modern, more flexible directive (supporting fine-grained rules like max-age and no-cache); Expires is an older, simpler date-based header - when both are present, Cache-Control generally takes precedence in modern browsers.
An ETag is a unique identifier for a specific version of a resource - it lets a browser ask "has this changed since I last saw ETag X?" and receive a lightweight "not modified" response instead of re-downloading unchanged content.
Frequently-updated content (a homepage, an API response) benefits from short or no caching so visitors always see current data; static assets that rarely change (a versioned CSS/JS file, a logo) benefit from long caching to avoid unnecessary re-downloads.
Despite the name, no-cache doesn't forbid caching - it means the cached copy must be revalidated with the server before being reused; "no-store" is the directive that actually prevents caching entirely.
It reports how long (in seconds) a cached response has been sitting in an intermediate cache (like a CDN) before being served to you - a high Age value confirms caching is actively working as configured.
Yes - overly aggressive caching (a long max-age on content that changes frequently) is a common, real cause of visitors seeing stale versions of a page after an update, until their cached copy naturally expires.