Check if a server supports HTTP/2 or HTTP/3. Protocol detection.
The HTTP/2 and HTTP/3 checker connects to a URL and reports which HTTP version the server uses (HTTP/1.1, HTTP/2, or HTTP/3/QUIC). Developers use it to verify TLS and ALPN negotiation, to confirm a CDN or origin supports HTTP/2, or to troubleshoot "protocol not supported" errors. May show ALPN negotiation and whether HTTP/3 (QUIC) is advertised.
Application-Layer Protocol Negotiation: TLS extension that lets client and server agree on h2 or http/1.1 over the same port.
The server or reverse proxy may not be configured for HTTP/2; enable it in nginx, Apache, or your host.
HTTP/3 runs over QUIC (UDP). A server that supports HTTP/3 must listen for QUIC and advertise it.
Browser support varies; a server-side check or dedicated tool gives a consistent result.
It makes a normal request; no more impact than opening the URL in a browser.