bevyengine/bevy

bevy_dev_tools

Developer-time utilities. The on-screen FPS overlay, state inspectors, picking debug overlays, frame-time graphs, and the framework for adding more.

Purpose

Things you want during development but not in shipping builds. The crate is gated behind the bevy_dev_tools cargo feature (and almost everything in it is feature-gated further). Standard practice is #[cfg(feature = "bevy_dev_tools")] around the plugin add.

Directory layout

crates/bevy_dev_tools/src/
├── lib.rs
├── fps_overlay/             # FpsOverlayPlugin (top-left FPS counter)
├── frame_time_graph/        # Frame-time graph overlay
├── states/                  # StateInspectorPlugin
├── picking_debug/           # Visualizes picking events
├── ci_testing/              # Drive an app for fixed frames in CI
└── …

Key abstractions

Type	File	Description
`FpsOverlayPlugin`, `FpsOverlayConfig`	`crates/bevy_dev_tools/src/fps_overlay/`	Toggleable FPS counter.
`FrameTimeGraphPlugin`	`crates/bevy_dev_tools/src/frame_time_graph/`	Rolling frame-time histogram overlay.
`StateInspectorPlugin`	`crates/bevy_dev_tools/src/states/`	Logs state transitions.
`DebugPickingPlugin`	`crates/bevy_dev_tools/src/picking_debug/`	Draws ray hits and pointer events.
CI testing utilities	`crates/bevy_dev_tools/src/ci_testing/`	Run an app for N frames and exit.

How it works

Each tool is its own Plugin. The FPS overlay reads from bevy_diagnostic::DiagnosticsStore and writes to a Text UI node. The state inspector observes StateTransitionEvent. The picking debugger draws gizmos from bevy_picking events.

Integration points

Depends on: bevy_app, bevy_diagnostic, bevy_text, bevy_ui, bevy_render, bevy_picking, bevy_state, bevy_color.
Depended on by: Examples and apps explicitly opting in.

Entry points for modification

Add a new dev tool as its own subdirectory + plugin. Match the pattern: feature-gate, register a single plugin, expose configuration as a resource.
The CI testing plugin is the right hook for automated screenshot tests.