bevy/docs/plugins_guidelines.md

# Third Party Plugin Guidelines

Bevy has a plug and play architecture, where you can easily add plugins for new features, or replace built-in plugins with your own.

This document targets plugin authors.

## Checklist

* [ ] [Pick a reasonable, descriptive name](#naming)
* [ ] [Bevy/plugin version support table](#bevy-version-supported)
* [ ] [Turn off default Bevy features](#bevy-features)
* [ ] [Choose a Bevy git/main tracking badge](#main-branch-tracking)
* [ ] [Pick a license](#licensing)
* [ ] [Remove unnecessary or redundant dependencies](#small-crate-size)
* [ ] [Add cargo tests and CI](#tests-and-ci)
* [ ] [Documentation and examples](#documentation-and-examples)
* [ ] [Publish your plugin](#publishing-your-plugin)
* [ ] [Promote your plugin](#promotion)

## Naming

You are free to use a `bevy_xxx` name for your plugin, but please be reasonable. If you are about to claim a generic name like `bevy_animation`, `bevy_color`, or `bevy_editor`, please ask first. The rationale is explained [here](https://github.com/bevyengine/bevy/discussions/1202#discussioncomment-258907).

## Promotion

You can promote your plugin in Bevy's [communities](https://github.com/bevyengine/bevy#community):

* Add it to [Awesome Bevy](https://github.com/bevyengine/awesome-bevy).
* Announce it on [Discord](https://discord.gg/bevy), in the `#showcase` channel.
* Announce it on [Reddit](https://reddit.com/r/bevy).

## Bevy Version Supported

Indicating which version of your plugin works with which version of Bevy can be helpful for your users. Some of your users may be using an older version of Bevy for any number of reasons. You can help them find which version of your plugin they should use. This can be shown as a simple table in your readme with each version of Bevy and the corresponding compatible version of your plugin.

|bevy|bevy_awesome_plugin|
|---|---|
|0.4|0.3|
|0.3|0.1|

## Bevy Features

You should disable Bevy features that you don't use. This is because with Cargo, features are additive. Features that are enabled for Bevy in your plugin can't be disabled by someone using your plugin. You can find the list of features [here](cargo_features.md).

```toml
bevy = { version = "0.4", default-features = false, features = ["..."] }
```

## Main Branch Tracking

If you intend to track Bevy's main branch, you can specify the latest commit you support in your `Cargo.toml` file:

```toml
bevy = { version = "0.4", git = "https://github.com/bevyengine/bevy", rev="509b138e8fa3ea250393de40c33cc857c72134d3", default-features = false }
```

You can specify the dependency [both as a version and with git](https://doc.rust-lang.org/cargo/reference/specifying-dependencies.html#multiple-locations), the version will be used if using the dependency from [crates.io](https://crates.io), the git dependency will be used otherwise.

Bevy is evolving very fast. You can use one of these badges to communicate to your users how closely you intend to track Bevy's main branch.

<!-- MD033 - The Badges could be downsized, without the inline HTML due to the large code colum -->
<!-- markdownlint-disable-next-line MD033 -->
|<div style="width:100px">badge</div>|<div style="width:200px">description</div>|code|
|-|-|-|
|[![Bevy tracking](https://img.shields.io/badge/Bevy%20tracking-main-lightblue)](https://github.com/bevyengine/bevy/blob/main/docs/plugins_guidelines.md#main-branch-tracking)|I intend to track main as much as I can|`[![Bevy tracking](https://img.shields.io/badge/Bevy%20tracking-main-lightblue)](https://github.com/bevyengine/bevy/blob/main/docs/plugins_guidelines.md#main-branch-tracking)`|
|[![Bevy tracking](https://img.shields.io/badge/Bevy%20tracking-released%20version-lightblue)](https://github.com/bevyengine/bevy/blob/main/docs/plugins_guidelines.md#main-branch-tracking)|I will only follow released Bevy versions|`[![Bevy tracking](https://img.shields.io/badge/Bevy%20tracking-released%20version-lightblue)](https://github.com/bevyengine/bevy/blob/main/docs/plugins_guidelines.md#main-branch-tracking)`|

## General Advices for a Rust Crate

This advice is valid for any Rust crate.

### Licensing

Bevy is dual licensed under [MIT or Apache 2.0](https://www.rust-lang.org/policies/licenses), at your option. Most other Rust projects (including Rust itself) also use this dual-license approach. MIT-only is very popular and you might be tempted to just use that (Bevy also used to be MIT-only), but there are [very good reasons](https://github.com/bevyengine/bevy/issues/2373) to include both and we highly recommend using the dual MIT / Apache-2.0 license for your Bevy Plugins and crates:

* Including the Apache 2.0 license option significantly reduces the difficulty and boilerplate of proper license compliance in published games because you only need to include one copy of the Apache 2.0 license.
* Provides maximum compatibility with Bevy and Rust, making it easier to upstream your changes.

### Small Crate Size

To avoid long build times in your crate and in projects using your plugin, you should aim for a small crate size:

* Disable Bevy features that you don't use
* Avoid large dependencies
* Put optional functionality and dependencies behind a feature

### Documentation and Examples

Documentation and examples are very useful for a crate.

In the case of a plugin for Bevy, a few screenshots or movies/animated GIFs from your examples can really help understanding what your plugin can do.

Additionally, it can be helpful to list:

* Stages added by the plugin
* Systems used
* New components available

### Tests and CI

Tests are always good! For CI, you can check [this example](https://github.com/actions-rs/meta/blob/master/recipes/quickstart.md) for a quickstart using GitHub Actions. As Bevy has additional Linux dependencies, you should install them before building your project, [here is how Bevy is doing it](https://github.com/bevyengine/bevy/blob/cf0e9f9968bb1bceb92a61cd773478675d35cbd6/.github/workflows/ci.yml#L39). Even if you don't have many (or any) tests, setting up CI will compile check your plugin and ensure a basic level of quality.

### Publishing your Plugin

There are some [extra fields](https://doc.rust-lang.org/cargo/reference/manifest.html) that you can add to your `Cargo.toml` manifest, in the `[package]` section:

|field|description|
|-|-|
|[`description`](https://doc.rust-lang.org/cargo/reference/manifest.html#the-description-field)|a description of the plugin|
|[`repository`](https://doc.rust-lang.org/cargo/reference/manifest.html#the-repository-field)|URL of the plugin source repository|
|[`license`](https://doc.rust-lang.org/cargo/reference/manifest.html#the-license-and-license-file-fields)|the plugin license|
|[`keywords`](https://doc.rust-lang.org/cargo/reference/manifest.html#the-keywords-field)|keywords for the plugin - `"bevy"` at least is a good idea here|
|[`categories`](https://doc.rust-lang.org/cargo/reference/manifest.html#the-categories-field)|categories of the plugin - see [the full list on crates.io](https://crates.io/categories)|
|[`exclude`](https://doc.rust-lang.org/cargo/reference/manifest.html#the-exclude-and-include-fields)|files to exclude from the released package - excluding the `assets` folder that you may have is a good idea, as well as any large file that are not needed by the plugin|

Once a crate is published to [crates.io](https://crates.io), there are two badges that you can add to your `README.md` for easy links:

|badge|code|
|-|-|
|[![crates.io](https://img.shields.io/crates/v/bevy)](https://crates.io/crates/bevy)|`[![crates.io](https://img.shields.io/crates/v/bevy_awesome_plugin)](https://crates.io/crates/bevy_awesome_plugin)`|
|[![docs.rs](https://docs.rs/bevy/badge.svg)](https://docs.rs/bevy)|`[![docs.rs](https://docs.rs/bevy_awesome_plugin/badge.svg)](https://docs.rs/bevy_awesome_plugin)`|