Bevy 0.20 — Router

Read this first when working on a Bevy project. All sibling skills assume Bevy 0.20 (0.20.0 released 2026-10-08; current patch 0.20.1, requires rustc 1.97.1). If the user's Cargo.toml pins a different version, stop and confirm before applying patterns from this collection.

Smallest valid app

use bevy::prelude::*;

fn main() {
    App::new()
        .add_plugins(DefaultPlugins)
        .add_systems(Startup, setup)
        .run();
}

fn setup(mut commands: Commands) {
    commands.spawn(Camera3d::default());
}

When to use which skill

Cardinal rules (every Bevy 0.20 task)

1. Events are messages. EventReader<E> / EventWriter<E> became MessageReader<M> / MessageWriter<M> in 0.17. Observers use On<E>, never Trigger<E>.
2. Lifecycle observers carry the bundle on the event. On<Add<Player>>, not On<Add, Player> (changed in 0.20). Replace became Discard in 0.19.
3. Pointer events are flat. On<PointerClick>, click.pointer.position; not On<Pointer<Click>> (0.20).
4. UI interaction is Hovered + Pressed. ui::Interaction and ui::widgets::Button are deprecated in 0.20; spawn ui_widgets::Button.
5. Text is FontSource + FontSize. TextFont { font: handle.into(), font_size: FontSize::Px(24.0) } (0.19). Default size is FontSize::Rem(1.) (0.20).
6. Shaders are WESL. .wesl, import a::b;, @if(DEF). naga_oil #import / #ifdef fail at asset load in 0.20.
7. Resources are components (0.19). Res<T> still works, but one type cannot be both Component and Resource.
8. Scenes: glTF spawns with WorldAssetRoot from bevy_world_serialization; bevy_scene is BSN (0.19).
9. No .unwrap() in systems. Use let ... else { return }; or a real error path.
10. Schedule order is explicit. Ambiguities are ignored by default (ScheduleBuildSettings::ambiguity_detection is LogLevel::Ignore); opt into LogLevel::Error to catch them. Built-in sets use .chain_weak() in 0.20, so cross-set ordering through channels or atomics needs an explicit .after().

Gotchas

• Bevy's training-data footprint is dominated by 0.10–0.16 code. If a snippet feels obvious, check it against the three migration skills before trusting it.
• bevy::prelude::* doesn't re-export everything. Hovered is bevy::picking::hover::Hovered; Pressed is the marker bevy::ui::Pressed (query with Has<Pressed>); Tonemapping is bevy::core_pipeline::tonemapping::Tonemapping; ScreenSpaceTransmission is bevy::pbr::ScreenSpaceTransmission.
• The bevy crate re-exports many subcrates (bevy_camera, bevy_light, bevy_material, bevy_extract, bevy_curve, bevy_shape, bevy_world_serialization, bevy_ui_widgets, bevy_feathers). Subcrate APIs are stable points to depend on for plugins.
• Deprecations (Interaction, set_if_neq, AssetId::invalid()) compile with warnings in 0.20 and will be removed later. Fix them now.

See also

• bevy-migration-0-19-to-0-20 — the latest catalogue of renames and breaks.
• bevy-cargo-features — what to put in Cargo.toml before any of the above will compile the way you want.