HTTP Header Checker

Free, no signup. See the headers browsers and crawlers receive: every redirect hop, separate security and SEO grades, edge fingerprints, compression, and an honest HTTP/3 signal.

Built by Patrick Stox

Request user-agent

A matching user-agent does not make this request originate from that crawler’s verified IP range.

This makes two user-triggered requests for one URL from Cloudflare infrastructure. It compares user-agent responses, not verified crawler behavior or crawler IP access.

Compare staging or another URL

The report compares the final response headers from two independent checks.

Checks run from our server; we fetch the URL you enter and don't keep the results. Complete response header maps are returned to your browser. Repeating the same URL and user-agent within about ten minutes may reuse a short-lived edge cache. Anonymous run-level outcome counters may be used for aggregate research; URLs, domains, IPs, and identifiers are never included, and no statistic is released below 100 runs.

Feedback
Report a bug

Found something broken in Http Header Checker? Let us know what happened — this goes straight to a private triage queue, not a public list.

What will be sent 
 No tool inputs, uploads, pasted source, complete results, query parameters, or URL fragments are attached automatically. You can edit or remove the selected passage above. Browser and anti-abuse metadata is processed for spam prevention. 
  
 
  
 
 
  
 
 
   
 
 Compare common headers across up to five URLs    
Frequency is calculated in this browser from the live final responses in this run. It is not a global popularity dataset.
   
 
 
Sample report
Illustrative example — exact grading for the fixed header map below
HTTP/2 200
strict-transport-security: max-age=31536000
cache-control: public, max-age=3600
etag: "abc123"
Security headers
F40/100
HSTS passes. Missing CSP fails; missing framing protection, Referrer-Policy, nosniff, Permissions-Policy, and COOP are warnings. Missing COEP is informational.
SEO headers
A+100/100
Cache-Control and ETag pass. Missing X-Robots-Tag, Link canonical, and Vary are informational in this HTTP-only grade.
The displayed HTTP/2 line is illustrative input only: the live Worker cannot expose the negotiated HTTP version.
 
 
 
How to use it
 
  1. Enter a public URL and choose the browser, search-crawler, or AI-crawler user-agent you want to send.
  2. Optionally add a staging or comparison URL; only final-response headers are diffed.
  3. Choose Check headers, start with the two grades, then inspect the exact finding and header evidence.
  4. Review every redirect response and use the raw curl-style view when you need to copy the complete observed map.
 
 
 
     
     
     
 
What the results mean
  • Security grade deducts 20 points per failure and 8 per warning across the implemented header rules.
  • SEO grade evaluates X-Robots-Tag, Link canonical and hreflang, Vary, cache directives, and ETag.
  • Pass confirms one rule; info is context without a score penalty.
  • Delivery fingerprint is evidence about a public edge, not proof of the origin host.
  • Comparison lists changed final-response header values, not HTML or behavior differences.
 
How it works
A bounded server-side checker sends the selected user-agent, records each redirect response without hiding intermediate headers, and returns normalized header maps and timings. Browser-side functions grade the final response, parse Link headers, inspect compression and protocol advertisements, identify a small set of edge fingerprints, produce a curl-style view, and diff an optional second final response. The small batch mode counts fields only across the final responses fetched in that run and labels names from a local status-preserving snapshot of the IANA HTTP Field Name Registry.
 
Features
  • Complete headers for every observed redirect hop.
  • Separate deterministic security and HTTP-level SEO grades.
  • Browser, Googlebot, and supported crawler user-agent choices.
  • Compression, edge fingerprint, and honest HTTP/3 advertisement facts.
  • Optional final-response environment diff and raw header export view.
  • Session-local common-header frequency for up to five URLs.
 
Limitations
 
The report cannot expose negotiated HTTP version, TLS certificate details, private origin infrastructure, or headers added only inside a user's network. The Fetch Headers API may combine repeated field lines: parsed combined values are assessed, but the original field-line order and boundaries cannot be reconstructed. User-agent strings originate from a Cloudflare datacenter, not verified crawler IP ranges. It does not inspect HTML metadata, application security, or whether a 200 body is correct.
 
Frequently asked questions
 
Does the tool preserve repeated header field lines?
Not exactly. The Worker Fetch Headers API exposes a normalized, potentially combined value. The checker parses and assesses that combined value, but it cannot reconstruct the original order or boundaries of repeated field lines.
Does this show the HTTP version?
Workers do not expose the negotiated HTTP version. The tool only reports when Alt-Svc advertises HTTP/3; that is not proof this request used HTTP/3.
Why do browser and Googlebot results differ?
Sites can vary headers by user-agent. This sends the selected user-agent string from a Cloudflare datacenter, not from a verified crawler IP rangeA crawler — also called a spider or bot — is an automated program that fetches web pages, extracts their links, and queues new URLs to visit. Search engines use crawlers to discover and download content for their index..
Are URLs saved?
No. The URL is fetched to build this report and a short-lived edge cache may reuse the same URL and user-agent response for about ten minutes.
Is a high security-header grade proof that a site is secure?
No. The grade covers a defined set of public response headers. It does not test application vulnerabilities, authentication, server configuration, dependency risk, or whether a policy works correctly for the application.
Does the SEO grade inspect HTML canonical and robots tags?
No. It evaluates HTTP-level signals such as X-Robots-TagThe X-Robots-Tag is an HTTP response header that carries the same indexing and serving directives as the robots meta tag (noindex, nofollow, nosnippet, and the rest). Because it lives in the header rather than the HTML, it's how you control indexing for non-HTML files like PDFs, images, and videos. and Link headers. Page-level canonical and robots elements require an HTML-aware checker.
 
Next stepHosting Checker — look up the exact spec and expected values.

People also explore
ToolDNS CheckerToolWebsite Down CheckerToolDomain ReportArticleMixed ContentArticleCaching for SEOArticleWebsite Hosting Migration SEO
 
 
 
Feature requests for Http Header Checker
 

Upvote what you want most. New ideas can be submitted from the floating Feedback menu;
      requests appear here once approved, and the most-wanted rise to the top.

   
Loading…
  
  ➕ Request a feature   
New requests are reviewed before they appear here.
 
     
  
  
 
 
 
 
    
 
 
    
 
Common issues & how to fix them
 
     
  •  Error HSTS is missing Fix: Serve Strict-Transport-Security on HTTPS responses, starting with a tested max-age and expanding to includeSubDomains only when every subdomain is HTTPS-ready. 
  •  Warning HSTS lifetime is short Fix: Raise Strict-Transport-Security max-age to at least 31,536,000 seconds after confirming HTTPS works across the covered hosts. 
  •  Error Content Security Policy is missing Fix: Add a Content-Security-Policy that allowlists the scripts, styles, images, frames, and connections the page actually needs, then tighten it from report-only to enforcement. 
  •  Warning Framing protection is missing Fix: Set Content-Security-Policy frame-ancestors to the origins allowed to embed the page, or use X-Frame-Options: DENY when embedding is never allowed. 
  •  Warning Referrer-Policy is missing Fix: Set Referrer-Policy to strict-origin-when-cross-origin, or a stricter policy that still supports the site’s analytics requirements. 
  •  Warning Referrer policy leaks full URLs Fix: Replace unsafe-url or origin-when-cross-origin with strict-origin-when-cross-origin so cross-origin requests do not expose full paths and query strings. 
  •  Information Cross-Origin Embedder Policy is missing Fix: If the page needs cross-origin isolation, set Cross-Origin-Embedder-Policy: require-corp and ensure every embedded cross-origin resource opts in; otherwise document that isolation is not required. 
  •  Error Multiple HTTP canonicals are present Fix: Emit exactly one HTTP Link header with rel="canonical" for the preferred URL and remove conflicting canonical targets at the edge or origin. 
  •  Error Vary star prevents useful caching Fix: Replace Vary: * with only the request headers that actually change the response, such as Accept-Encoding or Accept-Language, so caches can reuse it. 
  •  Warning Response varies by user agent Fix: Stop varying the full response on User-Agent where possible; use feature detection or a narrowly normalized device signal and confirm crawlers receive equivalent primary content. 
  •  Warning Googlebot receives restrictive caching Fix: Remove no-store/private caching sent specifically to Googlebot unless the content is genuinely personalized, and return the same cacheable public representation users receive. 
  •  Information Cache-Control is absent Fix: Set an explicit Cache-Control policy appropriate to the resource, using public max-age/s-maxage for reusable content or no-store for truly sensitive responses. 
  •  Information ETag is absent Fix: Add a stable ETag or Last-Modified validator for cacheable responses so clients can revalidate without downloading unchanged content. 
  •  Error X-Robots-Tag blocks indexing Fix: Remove noindex from the X-Robots-Tag on URLs intended for search, then verify the final response and request recrawling. 
    •