Is HTTP/2 Server Push still usable?

No, not in practice. Chrome removed support in version 106 (2022) and other engines followed, citing poor real-world performance and frequent over-pushing of already-cached resources. HTTP/3 never specified push at all. Treat it as deprecated and use 103 Early Hints instead.

What is a PUSH_PROMISE frame?

PUSH_PROMISE is the frame a server sends to reserve a new stream ID and declare the request it intends to push, before sending that response's HEADERS and DATA. It carries the promised request header block so the client can match or reject the resource.

How does a client decline a push?

The client sends RST_STREAM with error code CANCEL or REFUSED_STREAM on the promised stream. It can also disable push entirely by sending SETTINGS_ENABLE_PUSH = 0 in its SETTINGS frame, which most browsers now do.

What replaced Server Push?

The 103 Early Hints informational status combined with Link: rel=preload headers. The server sends 103 with preload hints while it computes the final response, letting the browser start fetching critical sub-resources without the server blindly pushing bytes the client may already have cached.

Does HTTP/3 support push?

No. The HTTP/3 specification (RFC 9114) deliberately omits Server Push. The industry consensus settled on 103 Early Hints as the forward-compatible mechanism for hinting critical resources early.

HTTP/2 Server Push Reference

Email me this result

Get this tool's output sent to your inbox, plus one useful tool a week. No spam, unsubscribe any time.

HTTP/2 Server Push let a server send resources to a client before they were requested, using a PUSH_PROMISE frame. In practice it under-delivered and is now removed from browsers. This reference documents how it worked and what to use instead.

How it works

A pushed resource follows this lifecycle on an HTTP/2 connection:

The server sends a PUSH_PROMISE frame on the client’s request stream, reserving a new server-initiated (even-numbered) stream ID and carrying the promised request header block.
The server then sends HEADERS + DATA for that pushed response on the reserved stream.
The client may accept it, or send RST_STREAM with CANCEL / REFUSED_STREAM to decline — useful when the resource is already in cache.
A client can disable push for the whole connection with SETTINGS_ENABLE_PUSH = 0.

The fatal flaw: servers routinely pushed resources the browser had already cached, wasting bandwidth, and push interacted badly with prioritization. Chrome removed it in v106 (2022), and HTTP/3 never specified push at all.

The modern replacement — 103 Early Hints

Instead of pushing bytes, the server sends an informational 103 Early Hints response carrying Link headers with rel=preload while it prepares the real response:

HTTP/2 103 Early Hints
Link: </app.css>; rel=preload; as=style
Link: </app.js>; rel=preload; as=script

HTTP/2 200 OK
Content-Type: text/html
...

The browser starts fetching the hinted resources immediately but stays in control of caching, so it never re-downloads something it already has. This is the recommended path on HTTP/2 and HTTP/3.