HTTP/3 Reachability
Probes six well-known endpoints and reports which protocol your browser actually negotiated. HTTP/3 (QUIC) runs over UDP and is often filtered or simply unreachable from networks that aggressively manage UDP traffic.
| Target | Protocol | Latency |
|---|---|---|
| Cloudflare anycast | … | — |
| Logrus | … | — |
How to read the table — h3 / h3-29 — HTTP/3 over QUIC, the path supports UDP-443. h2 — HTTP/2 over TCP, the fallback when QUIC isn't reachable or the server doesn't advertise Alt-Svc. http/1.1 — ancient, suggests a proxy stripping protocol upgrades. unknown — cross-origin response without Timing-Allow-Origin, so the browser hides the field.
Why HTTP/3 reachability matters
HTTP/3 carries traffic over QUIC, a UDP-based transport with 0-RTT handshake and built-in multiplexing. Most major CDNs advertise it via Alt-Svc, and modern browsers negotiate it automatically on the second visit to a domain. The catch: QUIC needs UDP-443 to pass cleanly. Many corporate firewalls, some ISPs, and most DPI systems either block UDP-443 outright or rate-limit it severely. In those environments the browser detects the failure and falls back to HTTP/2 over TCP-443 silently — the user only notices through slower connection setup. This tool fetches a tiny asset from each target and reads the negotiated protocol via the Performance API's `nextHopProtocol` field. h3 means QUIC won; h2 means the fallback fired. If a row shows 'unknown' it's not a failure — it's just that the cross-origin response didn't include Timing-Allow-Origin, so the browser hides the field per the spec.
Check something else
Each test answers a different question. Together they make a full picture of your connection.
Throttling Detector
Parallel speed measurements to popular services and control endpoints. See exactly who your ISP is throttling.
What's Blocked
Check connectivity to popular services (YouTube, Discord, Telegram, and more) across multiple protocol layers.
TLS Fingerprint
See your client through the eyes of DPI. Live JA3 and JA4 hashes, compared against common browsers.
QUIC not getting through is a signal too
A network that drops UDP usually drops other things too. Logrus does not depend on one transport: TLS, WebSocket, HTTP/2 and QUIC switch automatically to whatever actually works.
If it is not for you, do nothing: the access simply expires.
Technical tool for diagnosing the quality of a network connection. Does not provide means of access to information resources whose access is restricted under applicable law.