OpenTTD Development Documentation
External Links

OpenTTD GitHub
Contributing to OpenTTD - guidelines
OpenTTD Doxygen

General Reference

Coding style
Compiling OpenTTD
Add a setting
Add a squirrel function
Understanding the SaveGame handler
Bumping the savegame version
Doing an OpenTTD release

Language and Strings

Manual of style
Format of langfiles
Using OpenTTD strings
List of special strings

Window System

Using the window system
Colour codes that exist in OpenTTD
Adding a text box
Understanding the widget focus system
GUI style guide


The OpenTTD TCP protocol
The OpenTTD UDP protocol
Debugging desyncs
Server Admin Port development

Ingame Console

The console window
Console commands
Console variables
Using console scripting
Adding functions/commands to the console
Adding variables to the console
Console development history

Content APIs (modding frameworks)

Graphics and similar (NewGRF)
AI framework (NoAI)
GameScript framework (NoGO)
Social Integration

Other Reference

Map array (landscape grid)
Train acceleration
Sound IDs

The following information has not been confirmed for accuracy and may not be correct

Savegame File Format

Savegame files (including scenario files) consist of an 8-byte header followed by the actual savegame data in a compressed or plain form. Four types of file formats are supported by OpenTTD so far.


Offset Size Description
0 4 bytes Savegame format tag in plain text (see below)
4 uint32 Savegame version in big endian format (currently it's SAVEGAME_VERSION * 0x10000)

Savegame Format Tag

Tag Savegame body format
OTTD Data compressed using LZO
OTTN Plain data
OTTZ Data compressed using Zlib
OTTX Data compressed using LZMA