# SL:MP – Simple Lua Multiplayer for GTA: San Andreas

> SL:MP (Simple Lua Multiplayer): an open-source Lua multiplayer for GTA: San Andreas on MoonLoader, no SA:MP needed. SL:NET protocol, LuaJIT server, 2020–2021 releases.

- URL: https://pakulichev.com/en/projects/sl-mp
- Author: Pakulichev (https://pakulichev.com/)
- Language: en
- Updated: 2026-10-15
- Whole site for LLMs: https://pakulichev.com/llms.txt (index), https://pakulichev.com/llms-full.txt (full text)

## Facts

- **Type:** Multiplayer for GTA: San Andreas
- **Language:** Lua (MoonLoader, LuaJIT)
- **Client:** GTA: SA 1.0 US + MoonLoader
- **Server:** LuaJIT, Windows / Linux
- **Networking:** UDP, SL:NET protocol
- **Started:** August 2020
- **Latest release:** 1.0.0-alpha.1 (18.01.2021)
- **Authors:** Pakulichev, SEVEN
- **License:** open source

**SL:MP** (Simple Lua Multiplayer) is an open-source multiplayer for **GTA: San Andreas** that **SEVEN** and I developed in 2020–2021. It's written entirely in **Lua**: the client is a set of [MoonLoader](https://pakulichev.com/en/wiki/moonloader-lua-gta-sa) scripts running inside the game, and the server runs on **LuaJIT** for Windows and Linux.


![SL:MP banner: Simple Lua Multiplayer, developers Pakulichev and Seven.exe](https://pakulichev.com/img/sl-mp/slmp-banner.png "Project banner from the BLAST.HK thread, 2020")

## How the project started

It began in **August 2020** as an experiment: could we sync players using nothing but LuaSocket on top of SA:MP? It worked, and the experiment quickly turned into a project of its own.

How it evolved:

1. A prototype on top of SA:MP, with player positions sent via LuaSocket.
2. Then the SA:MP dependency was dropped, and the multiplayer ran on a **clean GTA: San Andreas 1.0 US** with only MoonLoader installed.
3. The protocol went from compressed JSON to serialized Lua tables and finally to the custom binary **SL:NET** protocol over UDP.
4. A standalone LuaJIT server for Windows and Linux appeared, along with a Java launcher and an ImGui interface.

The project thread on BLAST.HK opened on **August 23, 2020** with an "Exclusive" tag, and the first public release was out by **August 25**.

## Features

- on-foot sync within a configurable stream zone (about 10 players near each other in tests);
- vehicle sync for the driver and passengers;
- three types of dialogs: info, input field and list;
- pickups, including inside interiors;
- virtual worlds to separate players into dimensions;
- game patching examples using `memory` and LuaJIT FFI.

## Architecture

| Part | Technologies | Purpose |
| --- | --- | --- |
| Client | Lua, MoonLoader, LuaJIT FFI | Runs in the game, sends and applies sync |
| Server | LuaJIT, LuaSocket | Accepts players, broadcasts data, runs the game mode |
| Protocol | UDP, SL:NET | Binary packets with a custom bitstream |
| Launcher | Java, ImGui | Server list and connecting |

Later I moved the networking code into a separate library, **[SNET](https://pakulichev.com/en/projects/snet)**.

## Server configuration

The server is configured with the `server.cfg` file:

```ini
serverName = My SL:MP Server
version    = 1.0.0
gamemode   = freeroam
maxSlots   = 10
stream     = 200
address    = 0.0.0.0
port       = 7777
```

The default port is **7777**, same as SA:MP. The `serverName`, `gamemode` and `stream` values in the example are placeholders.

## Releases

| Version | Date |
| --- | --- |
| 0.0.1-Alpha | 25.08.2020 |
| Alpha rev.2 – rev.4 | 26–28.08.2020 |
| RC5, RC6 | 29.08.2020 |
| RC7 | 30.08.2020 |
| RC8 | 01.09.2020 |
| RC9 | 06.09.2020 |
| 0.0.1-RC-X | 12.09.2020 |
| **1.0.0-alpha.1** | **18.01.2021** |

Ten builds came out in the first month alone. The 0.0.1-RC-X client was downloaded over 200 times and the server (Windows and Linux) about 170 times; 1.0.0-alpha.1 got over 200 client downloads. The project repository has more than 120 commits.

## Team

I was the lead developer (about 100 of the 124 commits) and published the releases. **SEVEN** co-authored the project. Thanks to **imring**, **FYP** (the author of MoonLoader) and **Akionka**, who wrote the bitstream encoder for SL:NET.

I still count the SL:MP and SL Team days among the best times I had in GTA: San Andreas modding.

## FAQ

### Does SL:MP require SA:MP?

No. The first experiments ran on top of SA:MP, but the dependency was removed back in 2020: SL:MP runs on a clean GTA: San Andreas 1.0 US with MoonLoader.

### Who developed SL:MP?

SL:MP was developed by Pakulichev and SEVEN (the SL Team). The project credits imring, FYP and Akionka – the author of the bitstream encoder for the SL:NET protocol.

### How many players does SL:MP support?

The number of slots is set by the maxSlots parameter in server.cfg. During alpha testing the authors recommended no more than 10 players; in tests about 10 players near each other were synced.

### How is SL:MP different from SA:MP and MTA?

SA:MP and MTA are mature C/C++ multiplayers with their own clients. SL:MP is an experimental project where both the client and the server are written in Lua: you can read, modify and extend it without touching native code.