HTTP/3
The version of HTTP that runs over QUIC, a transport carried in UDP datagrams, so a lost packet delays less of the page than over TCP. CrawlCheck records whether a site advertises HTTP/3, through the Alt-Svc header or the DNS HTTPS record.
What HTTP/3 does not show
It helps visitors on slow or lossy networks; search and AI crawlers mostly fetch over HTTP/1.1 and HTTP/2, so HTTP/3 alone does not change what they read.
Where HTTP/3 comes up on this site
- How to check if your website supports HTTP/3HTTP/3 ( RFC 9114 ) carries web requests over QUIC, which runs on UDP datagrams instead of a TCP connection.
Terms this definition uses
Definitions that name HTTP/3
Related terms in HTTP, edge and rendering
The delivery layer between an origin and a client: proxies, caches, redirects, status codes and the headers that decide what a crawler actually received.
Content-Language header · Alt-Svc · HTTPS DNS record · Link header · content negotiation · Markdown negotiation · Retry-After · Server-Timing · WWW-Authenticate · Allow header · Content-Digest · Origin server · Reverse proxy · CDN · Edge node · WAF · Bot score · TLS handshake · DNS resolution · DNS timeout · Connection timeout · Read timeout · Redirect chain · Redirect loop · 301 redirect · 302 redirect · 307 redirect · 308 redirect · 304 response · 404 response · 410 response · 429 response · 500 response · 502 response · 503 response · 504 response · HEAD request · GET request · Content type · MIME sniffing · Content encoding · Compression · Brotli · ETag · Last-Modified · If-None-Match · Cache hit · Cache miss · Cache key · Vary header · Stale response · Stale-while-revalidate · Edge redirect · Origin bypass · Response parity · Header parity · hreflang · canonical URL · HSTS · HSTS preload list · Content-Security-Policy · CSP nonce · edge cache · cache split · cache-buster · Cache-Control · Age header · render-blocking resource · payload text share · lazy loading · 404 and 410 status codes
Questions about HTTP/3
What is HTTP/3?
The version of HTTP that runs over QUIC, a transport carried in UDP datagrams, so a lost packet delays less of the page than over TCP. CrawlCheck records whether a site advertises HTTP/3, through the Alt-Svc header or the DNS HTTPS record.
What does HTTP/3 not show or guarantee?
It helps visitors on slow or lossy networks; search and AI crawlers mostly fetch over HTTP/1.1 and HTTP/2, so HTTP/3 alone does not change what they read.
Which area of the glossary does HTTP/3 belong to?
HTTP, edge and rendering: The delivery layer between an origin and a client: proxies, caches, redirects, status codes and the headers that decide what a crawler actually received.
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