---
title: Login Compression
description: "Login 0x03, server → client."
---

`login` · `0x03` · **clientbound** (server → client)

Enables packet compression. Packets whose size is at least `threshold` bytes are sent zlib-compressed from this point on; a negative threshold disables compression. It may only be sent during login, before `LoginFinished`.

Sent by the server, read by the client. Listen for it with `client.on("LoginCompression", (data) => …)` on the receiving side.

## Fields

| Field | Type | Notes |
|---|---|---|
| `threshold` | VarInt | Minimum uncompressed packet size (ID + payload) to compress. `0`: always; negative: disabled. |

## Send it

```ts
// Server side with autoInit: false, before LoginFinished.
await client.sendPacket("LoginCompression", { threshold: 256 });
```

Packets of `threshold` bytes or more are zlib-compressed from the next packet on, in both directions. Sending it switches this server-side client automatically. `0` compresses everything, a negative value disables compression. Do not send it after `LoginFinished`.

Field aliases listed under Notes are accepted as alternative keys when writing.

Source: [`src/Core/Versions/776/Packets/login/clientbound/LoginCompression.ts`](https://github.com/GDLev/mc-protocol/blob/master/src/Core/Versions/776/Packets/login/clientbound/LoginCompression.ts)