What Are HTTP Headers?
HTTP headers are key-value pairs sent at the beginning of every HTTP request and response. They carry metadata like content type, cache directives, authentication credentials, encoding, and CORS permissions — invisible to the user but critical for how browsers and servers communicate.
Most Important HTTP Response Headers
Content-Type: tells the browser what kind of data is in the body (text/html, application/json). Cache-Control: controls caching behavior (max-age, no-store). Access-Control-Allow-Origin: enables cross-origin requests. X-Frame-Options: prevents clickjacking. Strict-Transport-Security (HSTS): forces HTTPS.
How to Read Headers Without DevTools
Our online HTTP Header Inspector fetches any public URL and displays all response headers in a readable table — including security grades, cache analysis, and CORS detection. This is useful for inspecting third-party APIs or checking production headers without browser DevTools.
Security Headers You Should Have
Every production website should have: Strict-Transport-Security, X-Content-Type-Options: nosniff, X-Frame-Options: SAMEORIGIN, Content-Security-Policy, and Referrer-Policy. Missing these headers exposes your site to XSS, clickjacking, and MIME sniffing attacks.