---
title: "HTTP/2 & HTTP/3 support check — Lemwatch Help"
description: "Confirms your server negotiates HTTP/2 and advertises HTTP/3 via Alt-Svc — a free performance win especially for mobile."
canonical: "https://lemwatch.com/help/http2-http3-support-check"
source: "https://lemwatch.com"
---

# HTTP/2 & HTTP/3 support check

> Confirms your server negotiates HTTP/2 and advertises HTTP/3 via Alt-Svc — a free performance win especially for mobile.

## Quick answer

 We negotiate ALPN and read the Alt-Svc header to detect HTTP/2 and HTTP/3 (QUIC) support per site.

## What it checks

- ALPN negotiation to h2

- Alt-Svc advertising h3

- Server push disabled (Chrome dropped support)

- 0-RTT indication on HTTP/3 (bonus)

## Where to find it in Lemwatch

 **Site details → Performance → Protocols.**

## How to fix

- Enable HTTP/2 in nginx ( listen 443 ssl http2; ).

- If on Cloudflare, HTTP/3 is one toggle away.

- For self-hosted HTTP/3, use Caddy or nginx-quic branch.

- Re-run the check.

## FAQ

### How much does HTTP/3 help?

 5-15% median TTFB improvement on lossy mobile networks.

### Do I need HTTP/3 if I have HTTP/2?

 Not critical, but it's a cheap win behind a CDN.

## Related

- Performance budgets

- Core Web Vitals

- Gzip/Brotli compression check


## Related

- [Help centre](https://lemwatch.com/help)
- [Setting Performance Budgets](https://lemwatch.com/help/performance-budgets)
- [Core Web Vitals Explained](https://lemwatch.com/help/core-web-vitals)
- [Gzip / Brotli compression check](https://lemwatch.com/help/gzip-brotli-compression-check)
- [Cache-Control header check](https://lemwatch.com/help/cache-control-header-check)
- [Lemwatch pricing](https://lemwatch.com/pricing)
- [Hysteresis band explained](https://lemwatch.com/help/hysteresis-band-explained)
- [HTML Validation Checks](https://lemwatch.com/help/html-validation)