HTTP/2 and HTTP/3 Checker
This tool does not contact the target server. Pasted headers stay in this browser; funnel steps use session storage in this tab and never place header data in the URL or our servers.
Paste the response header output from a client you trust. A status line can show the protocol that client observed; Alt-Svc can advertise HTTP/3, but it does not prove that a QUIC connection succeeded.
Results
This is a parser, not a network probe. It cannot verify current server support, redirects, certificates, TLS or ALPN negotiation, UDP reachability, or a successful HTTP/3 connection.
Paste response headers from a client you trust to identify the protocol in its status line and any HTTP/3 advertisement in Alt-Svc. Analysis stays in your browser. This parser does not contact the server or verify redirects, certificates, TLS, ALPN, UDP reachability, or a successful QUIC connection.
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