Web

HTTP/3 Test

HTTP/3 & QUIC

Test HTTP/3 support

Enter a domain name to check if HTTP/3 (QUIC) is enabled.

Tool features

Comprehensive HTTP/3 (QUIC) protocol detection
4 checks

HTTP/3 Detection

Check if your website supports HTTP/3 (QUIC) protocol

Performance Benefits

HTTP/3 provides faster connection establishment and improved performance

Modern Protocol

Verify support for the latest HTTP protocol standard

Alt-Svc Analysis

Analyze Alt-Svc headers to detect HTTP/3 availability

What is HTTP/3 & how it works

How QUIC makes the newest HTTP faster

HTTP/3 is the latest version of HTTP. Instead of running over TCP, it runs over QUIC — a transport built on UDP that combines the connection and TLS handshakes into one round-trip and eliminates the head-of-line blocking that can stall HTTP/2 on lossy networks.

Browsers discover HTTP/3 through an Alt-Svc response header advertising an h3 endpoint, then switch to QUIC on UDP port 443 for later requests. This test reads the Alt-Svc header, checks whether h3 and QUIC are advertised, and reports which protocols the host actually offers.

QUIC
The UDP-based transport HTTP/3 runs on, with built-in TLS 1.3.
Alt-Svc
The response header that advertises an h3 endpoint to browsers.
0-RTT
QUIC can resume sessions with zero round-trips, cutting connection latency.

How to use this tool

Test a domain's HTTP/3 support in four steps
1
Enter a domain
Type a domain name, e.g. example.com — the host is probed over HTTPS.
2
Run the test
Click Test HTTP/3 to fetch the response and inspect its Alt-Svc header for an h3 endpoint.
3
Review protocol support
See whether HTTP/3 and QUIC are advertised, alongside HTTP/1.1 and HTTP/2.
4
Read the handshake
Check the feature checks and raw handshake to confirm Alt-Svc, max-age and the negotiated protocol.

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Check HTTP status codes and response details for any URL with detailed analysis

Frequently asked questions

Common questions about HTTP/3
5 Q&A

HTTP/3 is the newest version of HTTP. It runs over QUIC (a UDP-based transport) instead of TCP, giving faster connection setup and no transport-level head-of-line blocking.

QUIC is the transport protocol HTTP/3 uses. Built on UDP with TLS 1.3 baked in, it merges the transport and encryption handshakes and handles packet loss per-stream, so one lost packet doesn't stall the whole connection.

A server advertises HTTP/3 with an Alt-Svc response header naming an h3 endpoint (e.g. Alt-Svc: h3=":443"). Browsers see it on a first HTTP/1.1 or HTTP/2 response, then upgrade to QUIC for subsequent requests.

Not immediately. Hosts typically offer HTTP/3 alongside HTTP/2 and HTTP/1.1, and clients that can't reach UDP/443 fall back automatically. This test reports support for all three.

Enable QUIC/HTTP/3 in your server or CDN (for example, the http3 listener in recent Nginx builds, or a toggle in Cloudflare) and ensure UDP port 443 is open. The server then adds the Alt-Svc header automatically.