--- title: "Bevy Agent" description: "An in-development Bevy 0.18 workspace for deterministic game simulation control, snapshots, replay, and JSON-RPC, HTTP, and WebSocket agents." url: "https://briansunter.com/projects/bevy-agent" --- May 13, 2026 In development Status checked Sep 15, 2026 # Bevy Agent An in-development Bevy 0.18 workspace for deterministic game simulation control, snapshots, replay, and JSON-RPC, HTTP, and WebSocket agents. [View Source](https://github.com/briansunter/bevy-agent) Rust Bevy Bevy Plugin ECS Reinforcement Learning Agents Simulation  ## Overview Bevy Agent is a Bevy plugin that turns a game into a deterministic simulation an external agent can drive tick-by-tick. Drop it into your `App`, register your gameplay state, and the plugin exposes `reset`, `step`, `snapshot`, `restore`, and `branch` over an in-process API, stdio JSON-RPC, HTTP, or WebSocket. I built it to make Bevy games usable as RL environments and as reproducible test harnesses, without leaving the regular Bevy plugin and ECS model.  Bevy Agent architecture diagram ## Features - Deterministic stepping via `SimClock` + a dedicated `AgentTick` schedule - Tier-1 snapshots of every registered resource and component, keyed by `StableEntityId` - Action logs, checkpoint indexes, and timeline branches for replay and what-if exploration - Optional headless PNG capture with tick/frame/size metadata - JSON-RPC over in-process, stdio, HTTP `POST /rpc`, or WebSocket - Rust API, an `agentctl` HTTP CLI, and a stdlib-only Python client ## Crates - `bevy_agent_core`: schedules, `SimClock`, domain actions, input frames, observations, rewards, terminal state, checksums - `bevy_agent_runner`: owns the `App`, exposes the control API and visual capture hooks - `bevy_agent_snapshot`: snapshots of registered resources and components with stable entity IDs - `bevy_agent_replay`: action logs, checkpoint indexes, timeline branches - `bevy_agent_remote`: JSON-RPC bridge with capability and session-token checks - `sample_platformer`: a headless reference game wired end-to-end into `AgentTick` ## Quick Start rust ``` use bevy_agent_core::AgentAction; use bevy_agent_runner::{AgentApp, ResetOptions}; let mut env = AgentApp::new(sample_platformer::build_headless_app); let obs0 = env.reset(ResetOptions::default())?; let step1 = env.step(AgentAction::Move { x: 1.0, y: 0.0 })?; let snapshot = env.snapshot()?; env.step(AgentAction::Jump)?; env.restore(snapshot.snapshot_id)?; let alternate = env.step(AgentAction::Noop)?; ``` Drive it from Python over HTTP: python ``` from bevy_agent_client import AgentClient env = AgentClient("http://127.0.0.1:4000/rpc") obs = env.reset(seed=42) step = env.step({"type": "Move", "x": 1.0, "y": 0.0}) snapshot = env.snapshot() env.restore(snapshot["snapshot_id"]) ``` ## Determinism Contract Gameplay systems that want replayable behavior should: - run in `AgentTick`, not the ordinary frame `Update` - read `SimClock`, not wall-clock `Time` - consume `CurrentInputFrame`, not keyboard or mouse state directly - use `StableEntityId` for semantic entity identity - register all gameplay state with `SnapshotAppExt` - keep rendering and UI systems read-only with respect to authoritative state ## Technology Stack - Rust 2024 edition, Bevy 0.18 - Custom `AgentTick` schedule for deterministic stepping - JSON-RPC transports: in-process, stdio, HTTP, WebSocket - `image` crate for PNG capture - Python client built on the standard library, no extra deps ## Availability The repository includes a publishing checklist and dry-run documentation, but no public crates.io package or other release artifact was verified during this audit. ## Related projects - [c-ecs](/projects/c-ecs) [An in-development single-header C99 entity-component-system library with caller-owned storage and compile-time capacities for small games and embedded targets.](/projects/c-ecs) - [Platform](/projects/platform) [A small 2D platformer rendered with isometric 3D models, written in C99 and built on Sokol and a tiny ECS. Same binary runs natively and in the browser via WebAssembly.](/projects/platform) - [Quantum Engine](/projects/quantum-engine) [A browser-first TypeScript ECS game-engine monorepo organized as 28 @quantum packages, with plugin-based rendering, physics, input, audio, animation, networking, UI, and scene editing.](/projects/quantum-engine) ## Share this project