What is HTTP/3 and why does it matter?

HTTP/3 is the latest version of the HTTP protocol and is built on QUIC (UDP port 443). It reduces latency, handles connection drops more gracefully and loads faster – especially on mobile networks. An HTTP/3 check shows whether your server already benefits from this.

What is the difference between "HTTP/3 advertised" and "HTTP/3 working"?

"HTTP/3 advertised" means the server signals HTTP/3 support via the Alt-Svc header. "HTTP/3 working" means a real QUIC connection (HTTP/3 only) was actually established. HTTP/3 is only fully active when both are true.

Why does the check say "NO" even though I configured HTTP/3?

Common causes: UDP port 443 is blocked by a firewall, the CDN or load balancer does not terminate HTTP/3 correctly, the HTTP/3 configuration is faulty, or the server does not answer QUIC requests within the time limit.

How does the HTTP/3 check work technically?

The check runs in two steps. First the Alt-Svc header is read over HTTP/1.1 or HTTP/2 to see whether HTTP/3 is advertised. Then curl opens a real QUIC connection using the --http3-only flag. Only a successful HTTP response over HTTP/3 counts as a pass.

Can I use the HTTP/3 check as an API?

Yes. The API is free and requires no signup. Just append format=json: https://h3check.de/?domain=example.com&host=auto&format=json. The response contains the Alt-Svc header, HTTP version, HTTP status code and further details.

HTTP/3 Check: www.hostinger.com – HTTP/3 active ✓

Stored result from Aug 10, 2026, 07:10 Check again now →

www.hostinger.com HTTP/3 active A real QUIC connection over UDP/443 was established.

HTTP/3 status

HTTP/3 advertised Whether the server signals via Alt-Svc that HTTP/3 is available.

YES

HTTP/3 working Whether a real QUIC connection (UDP/443) can be established and the page fetched over it.

YES

TLS version HTTP/3 mandates TLS 1.3 – QUIC supports nothing older.

TLS 1.3

IPv6 Whether an AAAA record is published in DNS.

YES

Server / CDN Detected from the Server response headers (last check).

Cloudflare

Show Alt-Svc header

h3=":443"; ma=86400

Nicely done – HTTP/3 is active.

The protocol side is already sorted. How fast your site actually loads for real visitors is what a free performance scan of www.hostinger.com with Core Web Vitals will tell you – takes about 30 seconds.

Want even more speed? turbopress hosting is tuned for WordPress performance (LiteSpeed, caching, security hardening).

Embed the badge

Show on your own site that you run HTTP/3. The badge updates with every new check.

Show HTML code

<a href="https://h3check.de/en/check/www.hostinger.com/"><img src="https://h3check.de/badge/www.hostinger.com.svg?lang=en" alt="HTTP/3 status of www.hostinger.com" width="191" height="30"></a>

API: /api/v1/check?domain=www.hostinger.com

HTTP/3 check & HTTP3 test – what does it mean?

This free HTTP/3 check tells you whether your website already uses the modern HTTP/3 protocol. An HTTP3 test is particularly useful when you are assessing the performance of your website, your WordPress hosting or your LiteSpeed/CDN configuration.

HTTP/3 is built on QUIC and normally uses UDP port 443. It can cut latency, handle connection drops more gracefully and often loads faster – especially on mobile networks. That is why so many people look for an HTTP3 check, QUIC test or HTTP/3 test.

We show two things. First, whether your server advertises HTTP/3 at all (via the Alt-Svc header). Second, whether a real HTTP/3 connection can actually be established. If your result is "NO", the cause is usually the server configuration, the CDN, blocked UDP/443, or simply that HTTP/3 has not been enabled yet.

Want HTTP/3 for WordPress without the tinkering? At turbopress hosting HTTP/3 is on by default (LiteSpeed Enterprise) – tuned for performance and security.

Keywords: HTTP/3 check, HTTP3 check, HTTP/3 test, HTTP3 test, QUIC check, QUIC test, h3 check.

HTTP/3 check (QUIC) for your domain

HTTP/3 status

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HTTP/3 check & HTTP3 test – what does it mean?