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Is It Down?SSL/TLS CheckerOpen Port CheckerOG Tag CheckerOCSP CheckerPing / LatencyHTTP InspectorRedirect ChainCSP AnalyzerTech Stack CheckerBetaTracerouteBetaHTTP/2 + HTTP/3robots.txt ViewerSSL Cert DecoderBanner GrabberWebSocket TesterCORS TesterHTTP TimingStructured DataPWA ManifestSEO Auditor
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Is It Down?SSL/TLS CheckerOpen Port CheckerOG Tag CheckerOCSP CheckerPing / LatencyHTTP InspectorRedirect ChainCSP AnalyzerTech Stack CheckerBetaTracerouteBetaHTTP/2 + HTTP/3robots.txt ViewerSSL Cert DecoderBanner GrabberWebSocket TesterCORS TesterHTTP TimingStructured DataPWA ManifestSEO Auditor
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HTTP/2 and HTTP/3 Checker

Check which HTTP protocol version a website uses and whether it advertises HTTP/3 (QUIC) support via the Alt-Svc header.

Examples:

Enter a domain to check HTTP/2 and HTTP/3 support

Related Tools

HTTP Inspector

Inspect response headers and grade the HTTP security configuration for any URL. One request - raw headers and an A‑F security score side by side.

Redirect Chain

Trace every HTTP redirect hop for any URL - see status codes, final destination, and timing per step.

Tech Stack Checker

Detect the technologies powering any website - CDN, web server, CMS, framework, and analytics. Detected from HTTP response headers and HTML source.

About this tool

HTTP/2 (RFC 7540) introduced multiplexing - multiple requests over a single TCP connection simultaneously. This eliminates the "head-of-line blocking" problem in HTTP/1.1 where one slow response would delay all subsequent ones. HTTP/2 is now used by over 60% of the web.

HTTP/3 (RFC 9114) replaces TCP with QUIC - a UDP-based transport layer. It improves performance on high-latency or lossy connections by eliminating TCP's handshake overhead and solving transport-level head-of-line blocking. When a server supports HTTP/3, it signals this by returning an Alt-Svc header with an h3 entry so browsers can upgrade future connections.

This check detects HTTP/3 advertisement only - actual HTTP/3 negotiation requires a browser with QUIC support. The check is performed from a Cloudflare edge node and requires HTTPS.