Test whether a website supports HTTP/2 and advertises HTTP/3 (QUIC) in its Alt-Svc header
Checked from our server in India. Only the address you type is sent to us; nothing else leaves your device. Checked against sources on 16 Oct 2026.An HTTP/2 checker tells you which HTTP version a website uses. This one connects from our server to port 443, offers HTTP/2 and HTTP/1.1 during the TLS handshake and reports the one the site picks, then reads the Alt-Svc header of the home page, which is how a site advertises HTTP/3 over QUIC to browsers.
Type the domain.
Press Check HTTP versions. Our server makes one TLS connection and one page request.
Read HTTP/2 and HTTP/3 in the headline and the Alt-Svc details below.
HTTP/2 is chosen inside the TLS handshake. The browser lists the protocols it speaks in an extension called ALPN, and the server picks one. This checker does the same from our server: it offers "h2" and "http/1.1" on port 443 and reports the server's choice. A site that answers "h2" serves HTTP/2 to every modern browser; one that picks "http/1.1", or ignores ALPN, does not.
HTTP/3 works differently. It runs over QUIC, on UDP rather than TCP, and a browser only tries it after an ordinary HTTPS response says it may, with a header such as Alt-Svc: h3=":443"; ma=86400. The checker requests the home page, follows up to five redirects, and reads that header from the last response that sent it. It shows the port, the host if another one is named, and how long the browser may remember the offer.
HTTP/2 yes and HTTP/3 yes is what large CDNs serve today. HTTP/2 no usually means an old web server version or a setting that is off; it is a one-line change on nginx, Apache, IIS and most hosting panels. HTTP/3 no is common and not a fault. Draft only means the server still advertises a pre-standard version such as h3-29, which current browsers ignore.
Our server does not speak QUIC, so HTTP/3 is reported as advertised, not as a completed connection; a firewall that blocks UDP port 443 can still stop it. The check runs from India and uses port 443 only.
Type the domain and press Check HTTP versions. Our server opens a TLS connection on port 443 and offers both HTTP/2 and HTTP/1.1 through ALPN, the way a browser does. If the site picks h2 the headline says HTTP/2 yes; if it picks HTTP/1.1 or ignores the offer, it says no.
A site advertises HTTP/3 in the Alt-Svc response header, for example h3=":443"; ma=86400. The checker requests the home page, follows redirects and reads that header. HTTP/3 yes means an h3 entry was found. Browsers then try QUIC on the next request if UDP port 443 is open.
HTTP/3 runs over QUIC on UDP, and our server's checks use TCP and TLS. The Alt-Svc header is the same signal browsers rely on before switching, so it shows the site's intent accurately. Whether QUIC then works also depends on firewalls between the visitor and the site.
The server advertises a pre-standard HTTP/3 version such as h3-29 or h3-Q050, but not the final h3 published as RFC 9114 in 2022. Current browsers no longer use the drafts, so they stay on HTTP/2. Updating the web server, proxy or CDN usually fixes it.
On nginx add http2 to the listen 443 ssl line, or use the http2 on directive in 1.25.1 and later. On Apache enable mod_http2 and set Protocols h2 http/1.1. Most CDNs and hosting panels have a switch. HTTP/2 needs HTTPS in browsers, so the site must already have a certificate.
Usually, for pages with many files. HTTP/2 sends many requests at once over one connection and compresses headers, so the browser does not queue requests behind six parallel connections as with HTTP/1.1. HTTP/3 adds faster connection set-up and better behaviour on lossy mobile networks.
Rates and rules change; check the source before you rely on a figure.
Still stuck? Ask about HTTP/2 and HTTP/3 Checker and anybody who knows can answer. No account needed.
Also works as: HTTP/3 Checker.
Same job, other tools: AAAA Record Lookup (IPv6) – Check whether a domain has an IPv6 address, and what it is · CNAME Lookup – Check where a CNAME alias points and follow the chain to its final address · DS Record Lookup – Read the DS record the parent zone holds and see whether it matches a published key · Domain Expiry Checker – Domain expiry check: the registry’s own expiry date, with the days left counted.