# Enable compression for WebSocket messages

> Enable permessage-deflate compression for WebSocket messages with the `perMessageDeflate` option of `Bun.serve()`.

Set the `perMessageDeflate` parameter to enable the [permessage-deflate](https://tools.ietf.org/html/rfc7692) WebSocket extension. Bun then negotiates compression with clients that support it. Messages sent with `ws.send()` and `ws.publish()` are still uncompressed unless you opt in per message (see below). Messages sent with `server.publish()` are compressed unless you opt out per message.

```ts server.ts icon="/icons/typescript.svg"
Bun.serve({
  // ...
  websocket: {
    // enable compression
    perMessageDeflate: true,
  },
});
```

---

To enable compression for individual messages, pass `true` as the last parameter to `ws.send()` or `ws.publish()`. This requires `perMessageDeflate` to be enabled; otherwise Bun sends the message uncompressed.

```ts server.ts icon="/icons/typescript.svg"
Bun.serve({
  // ...
  websocket: {
    perMessageDeflate: true,
    async message(ws, message) {
      // send a compressed message
      ws.send(message, true);
      // publish a compressed message to a topic
      ws.publish("chat", message, true);
    },
  },
});
```

---

`server.publish()` compresses by default. Pass `false` as the third parameter to publish a message uncompressed. Compression makes short messages larger, so pass `false` for those.

```ts server.ts icon="/icons/typescript.svg"
const server = Bun.serve({
  // ...
  websocket: {
    perMessageDeflate: true,
    open(ws) {
      ws.subscribe("chat");
    },
  },
});

// compressed for subscribers that negotiated the extension
server.publish("chat", JSON.stringify({ type: "snapshot", users: ["alice", "bob", "carol"] }));

// uncompressed for every subscriber
server.publish("chat", "ping", false);
```