Detects HTTP/3 and QUIC support via the Alt-Svc header.
This check looks for HTTP/3 support by examining the 'Alt-Svc' (Alternative Service) header in your server's response. HTTP/3 is the newest version of the web's communication protocol, built on a technology called QUIC. Unlike older protocols that use TCP, HTTP/3 uses UDP, which means it can establish connections faster and handle packet loss better — making it especially beneficial for users on mobile networks or in regions with high latency.
HTTP/3 can noticeably improve your website's loading speed, particularly for users on unstable or high-latency connections (like mobile networks, satellite internet, or users in geographically distant locations). It reduces connection setup time and is more resilient to the kind of packet loss that's common on wireless networks.
This is informational only. Not having HTTP/3 will NOT hurt your search rankings. However, adopting it can provide a real-world performance edge, especially for a global audience. Most major CDN providers (like Cloudflare and Fastly) offer HTTP/3 support automatically at no extra cost.
Run a free audit to see how your site performs on HTTP/3 Support and 159 other checks.
Start Free AuditChecks if images use responsive techniques like srcset.
Checks if images have width and height attributes to prevent layout shift.
Checks for JavaScript errors in the browser console. (Note: In-dev check)
Measures the total size of the HTML document.