Free HTTP Header Checker
Updated September 2026
Analyse pasted HTTP response headers for security, caching, and performance issues. Free online header checker — no URL fetching, paste headers from curl or DevTools.
Paste raw HTTP response headers below. Get them by running curl -I https://example.com in your terminal.
Diagnosing web and network issues quickly is critical for site owners, developers, and SEO professionals. The HTTP Header Checker delivers actionable data in seconds.
Analyse pasted HTTP response headers for security, caching, and performance issues. Free online header checker — no URL fetching, paste headers from curl or DevTools. Results are immediate — no waiting, no loading screens, no account required.
Who uses the HTTP Header Checker?
- Security engineers auditing web application response headers by pasting curl output for a quick compliance check.
- DevOps engineers verifying cache-control and CDN header configuration after deployment.
- Web developers learning which security headers to add to their server configuration.
Common uses and search terms
The HTTP Header Checker is frequently used for: http headers, response headers, header checker. Whether you need a quick result or are working through a longer project, the tool handles all common variations without any configuration.
Why use Allio Tools's HTTP Header Checker?
Everything runs locally in your browser. No data is sent to a server, logged, or stored anywhere. The tool is completely free with no usage limits, no premium tiers, and no account required. Available in 11 languages and optimised for all screen sizes, the HTTP Header Checker works on desktop, tablet, and mobile with no app download needed.
See also:IP Address Lookup · Website Speed Test · DNS Lookup
How the HTTP Header Checker works
Run `curl -I https://example.com` in your terminal (or copy headers from your browser's Network tab) and paste the raw output into the text area.
Click Analyze Headers to check each header against a fixed set of security and important-header categories.
View the color-coded checklist: green check (present) or red X (missing) for each of 7 tracked security headers.
Scroll to the full headers table below for every header found, sorted alphabetically and color-coded by category.
Tips & tricks
- There's no live URL fetch — you must paste raw header text; the placeholder shows the exact `curl -I` command to get it.
- There's no click-to-expand documentation panel — the security-header checklist just shows present/missing with the value inline, so cross-reference the FAQs below for what each header should contain.
- The tool parses the status line (HTTP/2 200, etc.) if it's the first pasted line and color-codes it green/amber/red by status code range.
- The full headers table below the security checklist sorts alphabetically and highlights security headers in green, other well-known headers (content-type, cache-control, etag, etc.) in your accent color.
Frequently Asked Questions
Can I just enter a URL instead of pasting headers?
No — this tool only parses headers you paste in as raw text. Get them first with `curl -I https://example.com` in a terminal, or copy them from your browser DevTools Network tab, then paste the output here.
Which HTTP security headers does this tool check?
Seven headers: Strict-Transport-Security (HSTS), Content-Security-Policy (CSP), X-Content-Type-Options, X-Frame-Options, X-XSS-Protection, Referrer-Policy, and Permissions-Policy. Each is marked present or missing with its value shown if present.
What is the Strict-Transport-Security (HSTS) header?
HSTS tells browsers to always use HTTPS for your domain. Recommended: Strict-Transport-Security: max-age=31536000; includeSubDomains; preload. The preload directive submits you to browser HSTS preload lists for maximum protection.
What does Content-Security-Policy (CSP) protect against?
CSP prevents XSS (cross-site scripting) attacks by specifying which sources of scripts, styles, images, and other resources are allowed. A strict CSP is one of the most effective defenses against injection attacks.
How do Cache-Control headers work?
Cache-Control: max-age=31536000 tells browsers to cache the resource for 1 year. no-cache means revalidate with server before using cached copy. no-store means never cache. For static assets with hashed filenames, use long max-age. For HTML, use no-cache.
Is my data safe when using the HTTP Header Checker?
Completely safe. The HTTP Header Checker processes everything locally in your browser. No input data, results, or usage information is ever transmitted to or stored on any server.
How current is the data returned by the HTTP Header Checker?
The HTTP Header Checker fetches live data in real time each time you run it. Results reflect the current state of the server or domain at the moment of the request.
Why does the HTTP Header Checker sometimes return different results than other tools?
Results depend on the real-time state of the target server and DNS propagation, which can vary by geographic region and caching TTL. If you see inconsistencies, wait a few minutes and re-test — DNS changes can take up to 48 hours to propagate fully worldwide.
Works with ChatGPT, Claude, Cursor, GitHub Copilot, VS Code, Poe and more — 106+ tools, zero data collection.