HTTP/2 & HTTP/3 Check Online

The HTTP Version Check tool on 101IP makes a real HTTPS request to a website while attempting to negotiate HTTP/2 via ALPN. It also inspects the Alt-Svc header for HTTP/3 (QUIC) support and, when curl supports it, attempts a direct HTTP/3 connection.

How HTTP/2 is detected

HTTP/2 is negotiated during the TLS handshake via the ALPN (Application-Layer Protocol Negotiation) extension. If the server supports h2, it signals this to the client during TLS and the connection upgrades to HTTP/2. The response status line will start with HTTP/2.

How HTTP/3 (QUIC) is detected

HTTP/3 runs over QUIC (UDP). Servers advertise support via the Alt-Svc response header, for example: h3=":443"; ma=86400. If the server-side curl library supports HTTP/3, the tool also attempts a direct QUIC connection.

Benefits of newer HTTP versions

HTTP/2: request multiplexing, header compression (HPACK), stream prioritisation;
HTTP/3: eliminates transport-level head-of-line blocking, faster connection setup (0-RTT), better performance on unstable networks.

Frequently Asked Questions

How can I tell if a website uses HTTP/3?

The main indicator is the presence of the Alt-Svc header in the server response, for example: Alt-Svc: h3=":443". Our tool displays this header in the check results. The negotiated protocol will also be shown as h3 if both the server and the client support QUIC.
Can a site support HTTP/2 even if the server responds with HTTP/1.1?

Yes, this can happen due to a misconfigured TLS ALPN extension. The server may be set up for H2 but fail to advertise it to the client. In that case our checker will show http/1.1 even with H2 enabled server-side. Check your web server config: Nginx needs the http2 directive, Apache requires the mod_http2 module.
What should I do if the check shows only HTTP/1.1 support?

This means your server or hosting provider does not support modern protocols. First contact your hosting provider — most modern platforms enable H2/H3 by default. If you manage the server yourself, upgrade the web server software (Nginx 1.25+, Apache 2.4.57+), enable TLS 1.3 with ALPN, and for HTTP/3 configure QUIC on port 443.