The Arcade Learning Environment (ALE) is a simple framework that allows researchers and hobbyists to develop AI agents for Atari 2600 games. It is built on top of the Atari 2600 emulator Stella and separates the details of emulation from agent design. This video depicts over 50 games currently supported in the ALE.

For an overview of our goals for the ALE read The Arcade Learning Environment: An Evaluation Platform for General Agents. If you use ALE in your research, we ask that you please cite this paper in reference to the environment. See the Citing section for BibTeX entries.

Features

• Object-oriented framework with support to add agents and games.
• Emulation core uncoupled from rendering and sound generation modules for fast emulation with minimal library dependencies.
• Automatic extraction of game score and end-of-game signal for more than 100 Atari 2600 games.
• Multi-platform code (compiled and tested under macOS, Windows, and several Linux distributions).
• Python bindings through nanobind.
• Native support for Gymnasium, the maintained fork of OpenAI Gym.
• Atari roms are packaged within the pip package.
• C++ based vectorizer for acting in multiple ROMs at the same time.
• WebAssembly support for running ALE in the Browser

Quick Start

The ALE currently supports three different interfaces: C++, Python, Gymnasium and WASM.

Python

You simply need to install the ale-py package distributed via PyPI:

pip install ale-py

Note: Make sure you're using an up-to-date version of pip or the installation may fail.

Note: Free-threaded CPython (the t ABI, e.g. python3.14t) aren't supported as OpenCV doesn't build compatible wheels on any system which is necessary for preprocessing. We will look to add support when OpenCV does.

You can now import the ALE in your Python projects with providing a direct interface to Stella for interacting with games

from ale_py import ALEInterface, roms

ale = ALEInterface()
ale.loadROM(roms.get_rom_path("breakout"))
ale.reset_game()

reward = ale.act(0)  # noop
screen_obs = ale.getScreenRGB()

Gymnasium

For simplicity for installing ale-py with Gymnasium, pip install "gymnasium[atari]" shall install all necessary modules and ROMs. See Gymnasium introductory page for description of the API to interface with the environment.

import gymnasium as gym
import ale_py

gym.register_envs(ale_py)  # unnecessary but helpful for IDEs

env = gym.make('ALE/Breakout-v5', render_mode="human")  # remove render_mode in training
obs, info = env.reset()
episode_over = False
while not episode_over:
    action = policy(obs)  # to implement - use `env.action_space.sample()` for a random policy
    obs, reward, terminated, truncated, info = env.step(action)

    episode_over = terminated or truncated
env.close()

To run with continuous actions, you can simply modify the call to gym.make above with:

env = gym.make('ALE/Breakout-v5', continuous=True, render_mode="human")

For all the environments available and their description, see gymnasium atari page.

A vectorized environment with preprocessing, written in C++, is also available with gym.make_vec("ALE/Breakout-v5", num_envs=10). See vector-environment for more information.

C++

The following instructions will assume you have a valid C++17 compiler and vcpkg installed.

We use CMake as a first class citizen, and you can use the ALE directly with any CMake project. To compile and install the ALE you can run

mkdir build && cd build
cmake ../ -DCMAKE_BUILD_TYPE=Release
cmake --build . --target install

There are optional flags -DSDL_SUPPORT=ON/OFF to toggle SDL support (i.e., display_screen and sound support; OFF by default), -DBUILD_CPP_LIB=ON/OFF to build the ale-lib C++ target (ON by default), and -DBUILD_PYTHON_LIB=ON/OFF to build the nanobind wrapper (ON by default).

Finally, you can link against the ALE in your own CMake project as follows

find_package(ale REQUIRED)
target_link_libraries(YourTarget ale::ale-lib)

WebAssembly

The ALE can be compiled to WebAssembly for use directly in web browsers, enabling interactive demos, educational tools, and browser-based RL experiments without any installation.

This be used through NPM (> npm install @farama/ale-wasm) or through a standalone compiled zip (see the release artifacts).

Example NPM usage:

import createALEModule from './ale.js';

const ALE = await createALEModule();
const ale = new ALE.ALEInterface();

await ale.loadROM('roms/breakout.bin');
ale.resetGame();

while (!ale.gameOver()) {
    const actions = ale.getMinimalActionSet();
    const action = actions[Math.floor(Math.random() * actions.length)];
    const reward = ale.act(action);
}

For more examples for NPM and standalone installs, see docs/wasm/.

Citing

If you use the ALE in your research, we ask that you please cite the following.

M. G. Bellemare, Y. Naddaf, J. Veness and M. Bowling. The Arcade Learning Environment: An Evaluation Platform for General Agents, Journal of Artificial Intelligence Research, Volume 47, pages 253-279, 2013.

In BibTeX format:

@Article{bellemare13arcade,
    author = {{Bellemare}, M.~G. and {Naddaf}, Y. and {Veness}, J. and {Bowling}, M.},
    title = {The Arcade Learning Environment: An Evaluation Platform for General Agents},
    journal = {Journal of Artificial Intelligence Research},
    year = "2013",
    month = "jun",
    volume = "47",
    pages = "253--279",
}

If you use the ALE with sticky actions (flag repeat_action_probability), or if you use the different game flavours (mode and difficulty switches), we ask you that you also cite the following:

M. C. Machado, M. G. Bellemare, E. Talvitie, J. Veness, M. J. Hausknecht, M. Bowling. Revisiting the Arcade Learning Environment: Evaluation Protocols and Open Problems for General Agents, Journal of Artificial Intelligence Research, Volume 61, pages 523-562, 2018.

In BibTex format:

@Article{machado18arcade,
    author = {Marlos C. Machado and Marc G. Bellemare and Erik Talvitie and Joel Veness and Matthew J. Hausknecht and Michael Bowling},
    title = {Revisiting the Arcade Learning Environment: Evaluation Protocols and Open Problems for General Agents},
    journal = {Journal of Artificial Intelligence Research},
    volume = {61},
    pages = {523--562},
    year = {2018}
}

If you use the CALE (Continuous ALE), we ask you that you also cite the following:

Jesse Farebrother and Pablo Samuel Castro. Cale: Continuous arcade learning environment. Advances in Neural Information Processing Systems, 2024.

In BibTex format:

@article{farebrother2024cale,
  title={C{ALE}: Continuous Arcade Learning Environment},
  author={Jesse Farebrother and Pablo Samuel Castro},
  journal={Advances in Neural Information Processing Systems},
  year={2024}
}