> For the complete documentation index, see [llms.txt](https://docs.lawnchair.app/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://docs.lawnchair.app/developers/architecture/project-overview.md).

# Project overview

This page provides a high-level overview of Lawnchair's origins and its architectural foundation. Understanding this context is required to navigate the codebase.

### Lawnchair and Launcher3

Lawnchair is a fork of [Launcher3](https://cs.android.com/android/platform/superproject/main/+/main:packages/apps/Launcher3/), the default home screen application in the Android Open Source Project (AOSP). Lawnchair is built upon the same codebase used for the stock Android launcher.

Launcher3 is designed as a core component of the Android operating system. This distinction influences its architecture:

* AOSP components prioritize stability, performance, and resource management across diverse hardware and Android versions.
* Lawnchair inherits design philosophies and legacy structures directly from AOSP. These patterns often differ from Modern Android Development (MAD) practices used in standalone applications.

### Characteristics inherited from AOSP

Lawnchair inherits several characteristics from its AOSP foundation:

* Deep system integration for features like the Recents screen (Quickstep) and gesture navigation.
* Variable performance where core AOSP features are generally responsive, while Lawnchair-specific features or areas undergoing refactoring may not yet achieve the same level of fluidity.
* Platform-level optimizations to maintain a minimal resource footprint.
* Resilience against system-wide crashes through robust error handling.

To dive deeper into the technical principles governing the codebase, refer to [AOSP design patterns](/developers/architecture/aosp-design-patterns.md) and [Lawnchair design patterns](/developers/architecture/lawnchair-design-patterns.md). You can also consult the Glossary for definitions of project-specific terminology.

### Project structure

Lawnchair is composed of multiple Gradle modules. The most important ones are listed below:

* `lawnchair`
  * Contains Lawnchair-specific code and UI. Generally, most changes should be done here.
* `src`
  * Contains the core code of Launcher3 with modifications.
* `quickstep`
  * Contains the implementation of QuickStep, which enables Recents integration
* [`platforms/frameworks/libs/systemui`](https://github.com/LawnchairLauncher/platform_frameworks_libs_systemui)
  * Contains multiple libraries in SystemUI used by Lawnchair. See the linked repository for further information.

### Code quality and testing

Lawnchair prioritizes feature availability and user-facing stability.

Currently, the project **does not utilize unit tests or automated UI tests**. Code quality is maintained through manual verification by contributors and core maintainers, alongside feedback from our community via GitHub issues and Nightly build testers.


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