HTTP Header Viewer
Free online HTTP header viewer. Inspect response headers from any URL — check security headers, caching policies, server info and more. Essential for debugging and security audits.
Enter a URL and click "Fetch Headers" to see the response.
How to Use HTTP Header Viewer
Enter a URL
Type a full URL (including https://) into the input field. The tool will make a request to fetch the response headers from that URL.
View Response Headers
The response headers are displayed in a table — status code, content type, server information, caching directives, security headers, and more.
Analyze the Results
Check for missing security headers (like Content-Security-Policy or X-Frame-Options), review caching behavior (Cache-Control, ETag), and verify the server technology (Server header).
Common Security Headers to Check
| Header | Purpose |
|---|---|
| Content-Security-Policy | Controls which resources (scripts, styles, images) the browser can load. Primary defense against XSS attacks. |
| Strict-Transport-Security | Forces the browser to use HTTPS for all future requests to this domain. Prevents SSL stripping attacks. |
| X-Frame-Options | Prevents the page from being embedded in an iframe on another site. Stops clickjacking attacks. |
| X-Content-Type-Options | Blocks the browser from MIME-sniffing the content type. Prevents certain types of content injection. |
| Cache-Control | Directs browsers and CDNs on how to cache the response. Critical for performance optimization. |
| Server | Reveals the web server software and version. Consider hiding this in production for security. |
Frequently Asked Questions
What are HTTP headers?
HTTP headers are key-value pairs sent between the client and server with every HTTP request and response. Request headers tell the server about the client (browser type, accepted formats, authentication tokens). Response headers tell the client about the response (content type, cache rules, security policies, server info). Headers are invisible to users but critical for security, performance, and debugging.
What security headers should I look for?
Key security headers include: Content-Security-Policy (prevents XSS attacks), Strict-Transport-Security (enforces HTTPS), X-Frame-Options (prevents clickjacking), X-Content-Type-Options (prevents MIME sniffing), and Referrer-Policy (controls referrer information). Missing these headers makes your site more vulnerable to common web attacks.
Why do I see a CORS error?
When fetching headers from a different domain via JavaScript, the target server must include Access-Control-Allow-Origin headers to permit cross-origin requests. If these headers are missing, the browser blocks the response. Our tool attempts the request, but some servers block cross-origin header requests. For those cases, use curl -I in the terminal or a server-side tool.
What can I learn from response headers?
Response headers reveal: what web server and version is running (Server header), what caching strategy is in place (Cache-Control, ETag, Expires), what security measures are deployed, whether compression is enabled (Content-Encoding: gzip), how the server handles redirects (Location header), and what content type is being served (Content-Type). This information is invaluable for debugging and security audits.
Why Check HTTP Headers?
HTTP headers are the control channel of the web. Every page load, every API call, every image and script — all of it flows through headers. Understanding what headers your site sends (and what headers your dependencies send) is fundamental to web development and security.
What Headers Reveal
- Security posture: Missing CSP or HSTS headers are red flags in security audits
- Performance configuration: Cache-Control and ETag headers determine how efficiently resources load
- Server technology: The Server header often reveals the exact software and version
- Redirect chains: 301/302 responses with Location headers show how URLs resolve
- Content negotiation: Vary and Content-Type headers show how the server selects response formats