Check the final canonical HTTPS address after all redirects. If HTTPS is not working yet, repair it first; a separate protocol test is unnecessary in that situation.

Browser check

  1. Open the website in Chrome or another Chromium-based browser.
  2. Open Developer Tools from the browser menu under More tools.
  3. Select the Network tab and reload the page.
  4. If Protocol is not visible, right-click the table headings and enable that column.
  5. h2 means HTTP/2, h3 means HTTP/3 and http/1.1 is the older protocol.

Terminal check

curl -sS -L -o /dev/null -w '%{http_version}\n' https://example.com/

To test HTTP/3 separately:

curl --http3 -sS -L -o /dev/null -w '%{http_version}\n' https://example.com/

If the local curl build reports that --http3 is unsupported, that is a limitation of the local program and does not prove that the website lacks HTTP/3. Verify with a browser or an external checker.

HTTP/2 should remain available when HTTP/3 is enabled because not every device and network can use QUIC.