---
title: How an X4 extension is organized
summary: The folders and layers of a regular extension: game data, ships, MD, Lua and localization.
section: start
kind: guide
status: reference
tags: ["X4","modding","architecture"]
sources: ["https://wiki.egosoft.com/X4%20Foundations%20Wiki/Modding%20Support/"]
---
## Layers of a regular mod


An extension can contain data, game scripts and UI code. A property change needs only a manifest and a targeted XML diff. Add other layers when the task requires them.



| File or folder | Purpose |
| --- | --- |
| `content.xml` | Identity, description, version and dependencies |
| `assets/` | Ships, equipment, models and macros |
| `index/` | Resource registration |
| `libraries/` | Wares, recipes and other data |
| `md/` | Mission Director event logic |
| `aiscripts/` | AI behavior and patches |
| `ui.xml`, `ui/` | UI registration and Lua |
| `t/` | Text and translations |


## Choose a route for your task


Start with [ship properties](wiki:editing-parameters), [a new ship variant](wiki:adding-ship), [a custom window](wiki:create-ui), [an MD event](wiki:md-cues) or [localized text](wiki:localization). A regular mod does not require a separate service, TCP transport or native DLL.



## UI and the game effect


Lua builds the window and receives input; MD can perform world logic. Send an event, validate the object, perform the action, return the actual result and then update the window. Do not put every world change in a drawing callback. The original diagram below illustrates that flow.




```text
Кнопка интерфейса
  → событие в MD
  → проверка объекта и выполнение действия
  → ответ в Lua
  → обновление окна
```

## Next step


New to programming? Read [how X4 code works](wiki:x4-code-basics) and the [syntax cheat sheet](wiki:x4-language-cheatsheet). [Your first extension](wiki:first-extension) introduces the manifest. [Dependencies](wiki:compatibility) explains how to separate your files from DLC and third-party resources.