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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 range.
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-Tag 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.

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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.

   
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Über das Tool
Prüfe jeden HTTP-Response-Header einer Weiterleitungskette mit getrennten Sicherheits- und HTTP-SEO-Graden, CDN-/Edge-Fingerabdrücken, Kompressionsdaten, ehrlicher HTTP/3-Werbung, roher curl-Ansicht und optionalem Umgebungs-Diff.
Der Bericht bewertet öffentliche Header-Signale; er beweist weder Sicherheit noch eine bestimmte Origin-Infrastruktur.
Funktionen
  • Vollständige Header für jeden beobachteten Redirect-Hop
  • Deterministische Sicherheits- und SEO-Grades mit einzelnen Befunden
  • Browser-, Googlebot- und unterstützte Crawler-User-Agents
  • Kompression, Edge-Fingerprint, HTTP/3-Hinweis, Roh-Export und optionaler Staging-Produktionsvergleich
Funktionsweise
Ein begrenzter serverseitiger Prüfer sendet den gewählten User-Agent, zeichnet jede Redirect-Antwort inklusive Zwischenheadern auf und liefert normalisierte Maps und Timings. Browserfunktionen bewerten die finale Antwort, parsen Link-Header, prüfen Kompression und Protokollwerbung, erkennen Edge-Fingerabdrücke und vergleichen optional eine zweite finale Antwort.
Einschränkungen
  • Der Sicherheitsgrad prüft keine Anwendungsschwachstellen, Authentifizierung, Serverkonfiguration, Abhängigkeitsrisiken oder tatsächliche Policy-Wirkung.
  • Die Fetch Headers API kann wiederholte Feldzeilen zusammenführen; kombinierte Werte werden bewertet, ursprüngliche Reihenfolge und Grenzen sind nicht rekonstruierbar.
  • User-Agent-Anfragen stammen aus einer Cloudflare-Datacenter-Infrastruktur, nicht aus verifizierten Crawler-IP-Bereichen. HTML-Metadaten und das Verhalten eines 200-Bodys werden nicht geprüft.
Häufig gestellte Fragen
Beweist ein hoher Sicherheits-Header-Grad, dass eine Website sicher ist?
Nein. Der Grad deckt eine definierte Menge öffentlicher Response-Header ab. Er testet keine Anwendungsschwachstellen, Authentifizierung, Serverkonfiguration oder korrekte Policy-Wirkung.
Zeigt das Werkzeug die HTTP-Version?
Nicht exakt. Der Worker meldet nur, wenn Alt-Svc HTTP/3 bewirbt. Das beweist nicht, dass diese Anfrage tatsächlich HTTP/3 verwendet hat.
Sind die URLs gespeichert?
Die URL wird für diesen Bericht abgerufen; ein kurzlebiger Edge-Cache kann dieselbe URL- und User-Agent-Antwort etwa zehn Minuten wiederverwenden. Eine dauerhafte Kontospeicherung findet nicht statt.
Prüft der SEO-Grad HTML-Canonical- und Robots-Tags?
Nein. Er bewertet HTTP-Signale wie X-Robots-Tag und Link-Header. Seitengenaue Canonical- und Robots-Elemente erfordern einen HTML-fähigen Prüfer.