SEOlust logo SEOlust
Website & Performance

HTTP/2 & HTTP/3 Protocol Checker

Check whether a site supports HTTP/1.1, HTTP/2, and HTTP/3 — see the negotiated version and Alt-Svc h3 advertisement, with performance notes. Free.

All tools

💡 What this checks

  • Which HTTP version your connection negotiates (HTTP/1.1, HTTP/2, or HTTP/3).
  • Whether HTTP/2 is enabled — a big, easy performance win over HTTP/1.1.
  • Whether HTTP/3 (over QUIC) is advertised via the Alt-Svc header.

Free HTTP/2 & HTTP/3 Protocol Checker

Find out which HTTP protocol version a website serves. Enter a URL to see whether it supports HTTP/1.1, HTTP/2, and HTTP/3, the version your connection negotiates, and plain-English notes on the performance impact. Free, no sign-up.

Why the HTTP version matters for speed

The HTTP protocol version affects how efficiently a browser can load your site. HTTP/1.1 handles one request at a time per connection, so browsers open many connections and requests queue up. HTTP/2 multiplexes many requests over a single connection, removing that bottleneck. HTTP/3 goes further, running over QUIC to cut connection setup time and cope better with packet loss. Serving a modern protocol is one of the easiest performance wins available.

How the checker works

It probes the connection directly:

  • It negotiates a connection that prefers HTTP/2 and reports the version actually used.
  • It reads the server's Alt-Svc header to detect advertised HTTP/3 support.
  • It shows a per-version supported / not-enabled result.
  • It explains what to do if a newer protocol is missing.

HTTP/1.1 vs HTTP/2 vs HTTP/3

Each generation solved the previous one's main limitation:

  • HTTP/1.1 — one request per connection at a time; browsers work around it by opening several connections.
  • HTTP/2 — multiplexes many requests over one connection, with header compression and server push.
  • HTTP/3 — runs over QUIC (UDP) instead of TCP, so it sets up faster and recovers from lost packets without stalling every stream.
  • All three can coexist; browsers pick the best one the server supports.

How HTTP/3 support is detected

HTTP/3 is negotiated differently from HTTP/2. A browser first connects over HTTP/1.1 or HTTP/2, and the server advertises HTTP/3 availability with an Alt-Svc response header (for example, Alt-Svc: h3=":443"). The browser then upgrades to HTTP/3 on the next connection. Because of this, the most reliable way to detect HTTP/3 support is to look for that h3 advertisement — which is exactly what this tool does, even when the checking client itself cannot speak HTTP/3.

How to enable HTTP/2 and HTTP/3

If your site is behind a modern CDN such as Cloudflare, Fastly, or a major cloud provider, HTTP/2 is usually on by default and HTTP/3 is often a single toggle in the dashboard. On your own server, HTTP/2 requires a reasonably recent version of Nginx, Apache, or LiteSpeed with HTTP/2 enabled and HTTPS configured (browsers only use HTTP/2 over TLS). HTTP/3 needs QUIC support, which the newest server versions and CDNs provide.

Pro tip

HTTP/2 and HTTP/3 only work over HTTPS, so make sure TLS is properly configured first. Enabling HTTP/2 is the higher-impact change for most sites and is almost always free and low-risk; HTTP/3 is a nice additional gain, especially for visitors on mobile or unreliable networks. To see the full set of response headers, pair this with our HTTP Response Headers Viewer.

FAQ

Is this HTTP protocol checker free?
Yes. It is completely free and requires no account or sign-up. Enter a URL to check its protocol support instantly.
How do I know if my site uses HTTP/2?
Enter your URL and the tool negotiates a connection preferring HTTP/2, then reports whether it was used. If it shows HTTP/2 as supported, your server has it enabled.
How is HTTP/3 support detected?
By reading the server's Alt-Svc header, which advertises HTTP/3 availability with an h3 entry. This is the standard way HTTP/3 is announced, so it is detectable even before a browser upgrades to it.
Does HTTP/2 require HTTPS?
In practice, yes. Browsers only use HTTP/2 over TLS, so you need HTTPS configured before HTTP/2 will be negotiated. The same applies to HTTP/3.
Is HTTP/2 worth enabling?
For almost every site, yes. It multiplexes requests over one connection, which speeds up page loads with little effort or risk, and it is free on most servers and CDNs.
Do I need HTTP/3?
It is optional but beneficial, especially for mobile users and lossy networks, because QUIC reduces connection setup time and handles packet loss better. Many CDNs enable it with one click.
Why does HTTP/3 show as unknown?
If the server did not return an Alt-Svc header during the check, HTTP/3 cannot be confirmed. Some setups only advertise it under certain conditions or after an initial visit.

Related tools

Pro tip: pair this tool with PageSpeed Insights Checker and View Source Code for a faster SEO workflow.