Does your server speak HTTP/2 so crawlers can fetch resources in parallel?
HTTP/2 lets crawlers load HTML, CSS, JavaScript, and images over one connection instead of opening many.
What this signal tests
We check whether your server supports HTTP/2, the protocol upgrade introduced in 2015 that replaces HTTP/1.1 for most modern traffic. HTTP/2 uses a single connection to multiplex many requests simultaneously (multiplexing), avoiding the head-of-line blocking that slows down HTTP/1.1. We detect support by reading the ALPN identifier negotiated during the TLS handshake - pass if it returns h2.
Why it matters for your visibility in AI
AI crawlers like GPTBot, ClaudeBot, and PerplexityBot fetch many resources per page: the HTML itself, then linked CSS, JavaScript, JSON-LD scripts, and sometimes images for multimodal models. Over HTTP/1.1, those requests queue serially or open many parallel connections; over HTTP/2, they share one fast connection. If your site is on HTTP/1.1, a crawler that wants ten resources from your page may take three times longer to finish, increasing the chance of timeout and reducing the number of pages it can fetch in a session. HTTP/2 has been the web standard for nearly a decade. Every mainstream server (nginx, Apache, Caddy, IIS) and every major CDN supports it. Sites still on HTTP/1.1 today are usually behind aging configuration that has not been touched since launch.
Pass criteria at a glance
| Criterion | Passes when |
|---|---|
| Negotiated protocol == 'h2'. |
How we test it
We open a TLS connection to your domain on port 443 and offer two protocols via the ALPN extension: h2 (HTTP/2) and http/1.1. Your server picks one. If it picks h2, the check passes. ALPN is part of the standard TLS handshake, so this happens transparently for every modern browser and crawler - we simply read the result.
Show technical detection method
TLS connection to host:443 with ALPN offering [h2, http/1.1]; read negotiated protocol.
If your site fails: how to fix it
- If you use a CDN such as Cloudflare, Vercel, Fastly, or AWS CloudFront, HTTP/2 is on by default - no action needed. Move your origin behind one of these and the upgrade is automatic.
- On nginx, add http2 to the listen directive: listen 443 ssl http2;. Reload nginx and verify with curl -I --http2 https://yourdomain.com/ that the response shows HTTP/2.
- On Apache, load mod_http2 and add Protocols h2 http/1.1 to your virtual host. Restart Apache and confirm using the same curl command.
- On Caddy, HTTP/2 is enabled by default with TLS. No config change is required - confirm via curl.
- If your origin uses a managed platform (Heroku, Render, Fly, Railway), HTTP/2 is typically already on for public traffic. Verify, then move on.
Quick facts
| Maturity | ESTABLISHED |
|---|---|
| Weight | medium |
| Category | Performance |
Primary sources
Related signals
Frequently asked questions
Do I need a CDN?
Not strictly, but it is the easiest way to enable HTTP/2 (and HTTP/3) without touching your server config. Cloudflare's free tier enables both protocols for any domain you point at it, in addition to caching and DDoS protection.
Is HTTP/2 widely supported?
Yes. Every browser since 2015, every major crawler, and every AI bot vendor supports HTTP/2. There is no compatibility risk to enabling it - clients that do not support it negotiate HTTP/1.1 via ALPN automatically.
Should I jump straight to HTTP/3?
Enable HTTP/2 first, since support is universal. Then add HTTP/3 (which is covered by a separate signal) as a further upgrade. HTTP/3 still benefits from HTTP/2 as a fallback for clients that cannot negotiate QUIC.
Will fixing this also improve my Google ranking?
Indirectly, yes. HTTP/2 reduces page load time, which improves Largest Contentful Paint and overall Core Web Vitals. The same change helps AI crawler completion rates and ranking signals at the same time.
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