Bevy project foundations

When to use

Load this when a new Bevy app needs a crate, a pin, and a place for feature code before gameplay systems exist. Folder names below are layout habits. They are not engine types.

ECS shape

• Crate: Getting Started says start with cargo init or cargo new my_project, then cargo add bevy. The same page's Cargo.toml sample still shows bevy = "0.19". The library pin on bevy-master is 0.20.0.
• Features: The bevy 0.20.0 crate page documents profiles (default, 2d, 3d, ui) and default-features = false when you want a smaller set. One sample on that page still shows version = "0.18". That sample is not the pin.
• App shell: App::new().run() (Apps page). use bevy::prelude::* brings in the guide's essentials. Plugins, systems, and resources are added on that App.
• Code layout: Split by feature in ordinary Rust modules if the crate grows. These pages do not define a required directory tree.

Coming from Godot

Godot idea	Bevy idiom
New project	cargo new plus the bevy dependency
Engine module toggles	Cargo features and profiles on the bevy crate
Feature folders	Rust modules you choose. Not a scene tree
Editor project file	Check the docs before adding a project manifest beside Cargo.toml.

Scope

• Getting Started still shows bevy = "0.19" and a v0.19.0 checkout example. Pin 0.20.0 from crates.io and docs.rs, not from that snippet.
• OS window, audio, and input dependencies are mentioned as a Setup page. Check that page for package names before writing them.
• Workspace members, feature-folder enforcement, and naming linters are not on these pages.

Expert Knowledge Delta

Target: Bevy 0.20+.

Core ECS types: Component, Resource, Query, Commands, Startup, Update, Fixed / FixedMain (bevy::time), .chain(), Plugin, DefaultPlugins, MinimalPlugins. Messages and observers are an ownership slot. See bevy-events-messaging for their APIs. Systems run in parallel unless .chain() orders the ones that conflict.

Who owns state

Piece	Owner	Who may mutate	Schedule
Data on one entity	Component	One system via Query	Update or FixedMain
One value for the whole app	Resource	One system	Startup to insert, then the schedule that reads it
Spawn	Commands	The spawning system	Startup for the initial world; later schedules for runtime spawn
Order that must not race	.chain()	The chained systems only	Same schedule
Plugin boundary	Plugin	build registers systems and resources	Before the app runs

Borrow rule: two systems that both mutably query the same component must be ordered (.chain()) or split so only one writes. Unrelated systems stay parallel. That is the ECS page rule, not a guess at a system-set API.

Decision

If you need	Do this	Do not
Per-entity data	Component + Query	A Godot node script
App-wide config or clock	Resource	Copy the value onto every entity
Stable simulation step	FixedMain and the Fixed clock	Tie simulation to raw frame Update
Startup spawn	Commands in Startup	Spawn from a render system
Cross-system notice that is not shared state	Message or observer slot in bevy-events-messaging	A new event type invented in this file
An API outside the documented set	Check the official docs first	A made-up crate or API

Load references/ecs-ownership.md for the ownership table.

NEVER

• Do not pin /0.20.0/ in docs URLs. WHY: links stay on latest; the 0.20 target is stated once in prose.

• Do not mutably query the same component from two unordered systems. WHY: the schedule runs systems in parallel unless .chain() orders them.

• Do not invent a physics, navigation, networking, or XR crate here. WHY: this skill only names documented Bevy crates and modules.

• No Godot project types, scenes, or autoloads in this crate. WHY: Bevy code stays idiomatic ECS and uses only documented Bevy APIs.

• No invented Cargo features beyond the profiles and collections on docs.rs. WHY: Bevy code stays idiomatic ECS and uses only documented Bevy APIs.

• No third-party crates. WHY: Bevy code stays idiomatic ECS and uses only documented Bevy APIs.

Reference

docs.rs links use the unversioned latest permalink. The library pin on bevy-master stays 0.20.0.

Official Documentation

• Migration guides - Unversioned hop index.
• bevy crate - Profiles, collections, and Cargo features (0.20.0).
• Getting started - cargo new / cargo add bevy. The version snippet is stale.
• Apps - App::new(), World, and Schedule.
• Examples - Example tree on the latest branch.

Related Skills

Prerequisites

• bevy-master - Library pin and which Bevy skill to load next.

Complements

• bevy-ecs-composition - Entities, components, and systems after the crate exists.
• godot-project-foundations - Equivalent Godot skill. Do not import Godot types.

Downstream / consumers

• bevy-app-resources - App-wide resources once the App exists.

Master

• bevy-master - Bevy router.