Speed Medium impact Easy 10–30 min (often at the host/CDN)

HTTP protocol version

HTTP/2 and HTTP/3 are faster than the old HTTP/1.1.

What it is

HTTP/2 and HTTP/3 are newer versions of the protocol that can transfer multiple files in parallel over a single connection, compress headers, and (HTTP/3) resist packet loss.

Why it matters

On old HTTP/1.1, files are transferred essentially one at a time, which slows down pages with multiple resources. Switching to HTTP/2+ speeds up loading without touching the code.

How to do it

1Check your host/CDN for HTTP/2 and HTTP/3 support and enable them.
2It requires HTTPS (another reason to have a certificate).
3On HTTP/2, aggressive bundling stops making sense, so smaller files are OK.

Conclusion

A protocol upgrade is usually a painless win: often it's enough to enable it at the host or deploy a CDN. It requires HTTPS. It speeds up mainly sites with a larger number of resources.