HTTP/3 is the third major version of the Hypertext Transfer Protocol — the foundation of data exchange on the web. Unlike its predecessors, HTTP/3 is built on QUIC, a transport protocol that runs over UDP instead of TCP. You can check whether you are currently using HTTP/3 on whatsmy.fyi.
A Brief History of HTTP
Understanding why HTTP/3 is significant requires knowing where it came from:
- HTTP/1.0 (1996): One request per TCP connection. Extremely slow for pages with many resources.
- HTTP/1.1 (1997): Introduced persistent connections and pipelining, but suffered from head-of-line blocking — one slow resource blocked everything behind it.
- HTTP/2 (2015): Added multiplexing (multiple requests over one connection) and header compression. Major improvement, but still blocked by TCP-level head-of-line blocking.
- HTTP/3 (standardised 2022): Replaced TCP with QUIC, eliminating head-of-line blocking at the transport layer. Built-in encryption. Faster connection establishment.
What Is QUIC?
QUIC (Quick UDP Internet Connections) is a transport layer protocol developed by Google in 2012 and standardised by the IETF in 2021 (RFC 9000). QUIC runs on top of UDP (User Datagram Protocol) rather than TCP (Transmission Control Protocol).
The key advantages QUIC provides over TCP:
- No head-of-line blocking: In TCP, packet loss causes all streams to wait. In QUIC, each stream is independent — a lost packet only affects the stream it belongs to.
- 0-RTT and 1-RTT handshakes: TCP + TLS requires 2–3 round trips to establish a connection. QUIC combines the transport and encryption handshakes, cutting this to 1-RTT for new connections and 0-RTT for resumed connections.
- Connection migration: A QUIC connection is identified by a Connection ID, not the IP address and port. This means your connection survives network changes — switching from Wi-Fi to cellular no longer drops your connection.
- Built-in TLS 1.3: QUIC always encrypts traffic. There is no unencrypted QUIC.
HTTP/3 Performance Benefits
The performance improvements of HTTP/3 are most visible in two scenarios:
- High-latency networks: Mobile connections, satellite internet, or long-distance connections benefit most from the reduced handshake overhead.
- Lossy networks: Wi-Fi and mobile networks experience packet loss regularly. HTTP/3's per-stream loss recovery prevents one dropped packet from freezing an entire page load.
On low-latency, reliable connections (fast wired broadband), the difference between HTTP/2 and HTTP/3 is less noticeable but still present.
How to Check If You Are Using HTTP/3
The easiest way is to visit whatsmy.fyi — the HTTP Protocol card shows whether your connection used HTTP/1.1, HTTP/2, or HTTP/3 (QUIC).
You can also check in Chrome DevTools: open the Network tab, right-click the column headers, enable "Protocol", and look for h3 in the protocol column for resources loaded over HTTP/3.
Which Sites and CDNs Support HTTP/3?
HTTP/3 is widely supported by major CDNs and platforms:
- Cloudflare — HTTP/3 by default on all plans
- Google — all Google services support HTTP/3
- Meta (Facebook, Instagram) — HTTP/3 supported
- Fastly, Akamai, Amazon CloudFront — HTTP/3 supported
whatsmy.fyi runs on Cloudflare Workers, so if your browser supports HTTP/3, your connection is automatically upgraded.
Does HTTP/3 Replace TLS?
No. HTTP/3 uses TLS 1.3 internally as part of the QUIC protocol. You cannot use HTTP/3 without encryption. This is an improvement over HTTP/2, where HTTPS is technically optional (though universally used in practice). Learn more about TLS encryption.
Frequently Asked Questions
Is HTTP/3 supported by all browsers?
As of 2025, Chrome, Firefox, Safari, and Edge all support HTTP/3. Opera and Brave (both Chromium-based) also support it. Internet Explorer does not, but it is no longer supported by Microsoft.
Why am I using HTTP/1.1 instead of HTTP/3?
Several factors can prevent HTTP/3 upgrades: some corporate firewalls block UDP traffic (which QUIC uses), causing browsers to fall back to TCP-based HTTP/2 or HTTP/1.1. Some network middleboxes and proxies also interfere with QUIC.
Is HTTP/3 faster for everyone?
HTTP/3 provides the most benefit on high-latency or unreliable connections. On fast, stable wired connections, the difference is minimal. However, it is always at least as fast as HTTP/2 and typically faster.
