HTTP Headers Checker
Inspect HTTP response headers, security headers, content encodings, and server configurations for any URL.
HTTP Response Diagnostics
Enter any HTTP or HTTPS URL above and click Inspect Headers to analyze response codes, caching policies, and security headers.
About HTTP Headers Checker
HTTP response headers govern how web browsers cache assets, render frames, enforce HTTPS security, and handle cookies. Headers such as Content-Security-Policy, Strict-Transport-Security, and X-Content-Type-Options protect modern websites from cross-site scripting and clickjacking attacks.
Developers configuring web servers like Apache, Nginx, Cloudflare, or Vercel must test header configurations to ensure security headers are sent correctly and caching policies match performance targets.
This HTTP header and response inspector tests HTTP response headers and status codes against web endpoints. You can review response status descriptions, security header grades, content encodings, and cache-control directives in real time.
To debug server configurations, look up response codes via the HTTP status lookup and resolve host records using the DNS lookup.
Step-by-step practical guide
- Select a sample HTTP status code or enter a target API testing endpoint.
- Choose the HTTP request method: GET, POST, HEAD, or OPTIONS.
- Click Inspect Headers to send the test request and evaluate the response.
- Review the HTTP status code badge (such as 200 OK, 301 Moved Permanently, or 404 Not Found).
- Inspect the Security Headers evaluation checklist to see if modern security headers are enabled.
- Review the full raw header list and click Copy Headers to copy the configuration for documentation.
Engineering specifications and execution details
Tests HTTP responses using standard Fetch API requests with CORS-compliant inspect modes.
Evaluates key security headers: Strict-Transport-Security (HSTS), Content-Security-Policy (CSP), X-Frame-Options, X-Content-Type-Options, and Referrer-Policy.
Decodes standard HTTP response status codes defined by IETF RFC 9110.
Parses Cache-Control headers to calculate asset expiration intervals and public vs private caching.
Includes complete offline dictionary of all 63 official IANA HTTP status codes with technical explanations.
Data privacy and memory isolation
Requests are dispatched directly from your browser client without passing through private proxy relays.
Zero test URLs, header responses, or authorization tokens are stored on our servers.
Common production use cases
- Web security professionals auditing website security headers for compliance with OWASP guidelines.
- DevOps engineers verifying that Nginx or Apache server configuration blocks apply proper cache headers.
- Frontend developers diagnosing Cross-Origin Resource Sharing (CORS) preflight failures and header blocks.
- API developers checking Content-Type and charset encoding declarations across JSON and XML endpoints.
- System administrators confirming that HTTP to HTTPS 301 redirects operate correctly.
Edge cases and operational boundaries
- CORS restricted headers: Web browsers restrict in-browser access to certain server headers unless exposed via Access-Control-Expose-Headers; standard headers are audited.
- Redirect loops: Endpoints returning repeating 301/302 redirects are flagged to alert administrators to redirect chains.
- Missing HSTS headers: Websites lacking Strict-Transport-Security are highlighted with security recommendations.
- Custom header prefixes: Non-standard proprietary headers (such as X-Powered-By) are parsed and displayed cleanly.
Frequently Asked Questions
What is Content-Security-Policy (CSP) and why is it important?
CSP is an HTTP security header that restricts which domains can load scripts, images, and styles on your page, mitigating Cross-Site Scripting (XSS) attacks.
What is Strict-Transport-Security (HSTS)?
HSTS instructs web browsers to only communicate with a domain over secure HTTPS connections, preventing man-in-the-middle protocol downgrade attacks.
What does the X-Frame-Options header do?
X-Frame-Options indicates whether a browser should be allowed to render a page in an iframe, preventing clickjacking attacks where malicious sites overlay transparent frames.
Why does Cache-Control max-age matter for web performance?
The max-age directive tells browsers how many seconds to cache an asset locally, eliminating redundant server requests and speeding up page loads.
What does HTTP status code 304 Not Modified mean?
Status 304 indicates that the requested resource has not changed since the last fetch, allowing the client to use its cached copy to save bandwidth.
Can this tool inspect internal localhost endpoints?
Yes. Because the inspector executes directly inside your browser, it can send requests to local development servers on localhost with appropriate CORS headers.