HTTP Headers Viewer

What Are HTTP Headers?

HTTP headers are key-value pairs sent between a client (such as a web browser) and a server as part of every HTTP request and response. They carry metadata that controls how the communication is handled -- from specifying the content type and encoding of the response body to managing caching behavior, authentication, and security policies. HTTP headers are invisible to most end users but play a critical role in how web applications function, perform, and protect data. Inspecting response headers is an essential technique for web developers, SEO professionals, and security analysts when debugging issues or auditing website configurations.

Common HTTP Response Headers

Understanding the most important HTTP headers helps you diagnose performance problems, fix caching issues, and harden your website's security posture:

• Content-Type -- Specifies the media type of the response body (e.g., text/html, application/json). This header tells the browser how to interpret and render the received data.
• Cache-Control -- Directs how and for how long the response should be cached by browsers and intermediate proxies. Proper cache configuration significantly improves page load performance and reduces server load.
• Content-Encoding -- Indicates the compression algorithm used (e.g., gzip, br for Brotli). Compression reduces transfer size and speeds up page delivery.
• Access-Control-Allow-Origin (CORS) -- Controls which external domains are permitted to make requests to your server. CORS headers are essential for APIs and single-page applications that make cross-origin requests.
• Strict-Transport-Security (HSTS) -- Instructs browsers to only connect to the site over HTTPS, preventing protocol downgrade attacks and cookie hijacking.
• X-Content-Type-Options -- When set to nosniff, prevents browsers from MIME-type sniffing, reducing the risk of drive-by download attacks.
• Content-Security-Policy (CSP) -- Defines approved sources for scripts, styles, images, and other resources, providing a powerful defense against cross-site scripting (XSS) and data injection attacks.
• X-Frame-Options -- Controls whether the page can be embedded in iframes, protecting against clickjacking attacks.

Debugging and Analyzing HTTP Headers

Viewing HTTP response headers is one of the first steps when troubleshooting web application issues. Headers reveal whether a page is being served from a cache or the origin server, what compression is applied, whether security policies are correctly configured, and which server software is running. Missing security headers can leave your site vulnerable to common attacks, while incorrect caching headers can cause stale content to be served to users. Our free HTTP headers viewer tool fetches and displays all response headers for any URL along with the HTTP status code, making it easy to verify your server configuration, audit security headers, and diagnose content delivery problems without needing browser developer tools.