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PyPi Version Main License: MIT Python 3.7+ Code style: black


mbrl is a toolbox for facilitating development of Model-Based Reinforcement Learning algorithms. It provides easily interchangeable modeling and planning components, and a set of utility functions that allow writing model-based RL algorithms with only a few lines of code.

See also our companion paper.

Getting Started


Standard Installation

mbrl requires Python 3.8+ library and PyTorch (>= 1.7). To install the latest stable version, run

pip install mbrl

Developer installation

If you are interested in modifying the library, clone the repository and set up a development environment as follows

git clone
pip install -e ".[dev]"

And test it by running the following from the root folder of the repository

python -m pytest tests/core
python -m pytest tests/algorithms

Basic example

As a starting point, check out our tutorial notebook on how to write the PETS algorithm (Chua et al., NeurIPS 2018) using our toolbox, and running it on a continuous version of the cartpole environment.

Provided algorithm implementations

MBRL-Lib provides implementations of popular MBRL algorithms as examples of how to use this library. You can find them in the mbrl/algorithms folder. Currently, we have implemented PETS, MBPO, PlaNet, we plan to keep increasing this list in the future.

The implementations rely on Hydra to handle configuration. You can see the configuration files in this folder. The overrides subfolder contains environment specific configurations for each environment, overriding the default configurations with the best hyperparameter values we have found so far for each combination of algorithm and environment. You can run training by passing the desired override option via command line. For example, to run MBPO on the Gymnasium version of HalfCheetah, you should call

python -m mbrl.examples.main algorithm=mbpo overrides=mbpo_halfcheetah 

By default, all algorithms will save results in a csv file called results.csv, inside a folder whose path looks like ./exp/mbpo/default/gym___HalfCheetah-v2/; you can change the root directory (./exp) by passing root_dir=path-to-your-dir, and the experiment sub-folder (default) by passing experiment=your-name. The logger will also save a file called model_train.csv with training information for the dynamics model.

Beyond the override defaults, You can also change other configuration options, such as the type of dynamics model (e.g., dynamics_model=basic_ensemble), or the number of models in the ensemble (e.g., dynamics_model.model.ensemble_size=some-number). To learn more about all the available options, take a look at the provided configuration files.

Supported environments

Our example configurations are largely based on Mujoco, but our library components (and algorithms) are compatible with any environment that follows the standard Gymnasium syntax. You can try our utilities in other environments by creating your own entry script and Hydra configuration, using our default entry as guiding template. See also the example override configurations.

Without any modifications, our provided can be used to launch experiments with the following environments:

You can test your Mujoco and PyBullet installations by running

python -m pytest tests/mujoco
python -m pytest tests/pybullet

To specify the environment to use for, there are two possibilities:

  • Preferred way: Use a Hydra dictionary to specify arguments for your env constructor. See example.
  • Less flexible alternative: A single string with the following syntax:
    • mujoco-gym: "gym___<env-name>", where env-name is the name of the environment in Gymnasium (e.g., "HalfCheetah-v2").
    • dm_control: "dmcontrol___<domain>--<task>, where domain/task are defined as in DMControl (e.g., "cheetah--run").
    • pybullet-gym: "pybulletgym___<env-name>", where env-name is the name of the environment in pybullet gym (e.g., "HopperPyBulletEnv-v0")

Visualization and diagnostics tools

Our library also contains a set of diagnostics tools, meant to facilitate development and debugging of models and controllers. With the exception of the CPU-controller, which also supports PyBullet, these currently require a Mujoco installation, but we are planning to add support for other environments and extensions in the future. Currently, the following tools are provided:

  • Visualizer: Creates a video to qualitatively assess model predictions over a rolling horizon. Specifically, it runs a user specified policy in a given environment, and at each time step, computes the model's predicted observation/rewards over a lookahead horizon for the same policy. The predictions are plotted as line plots, one for each observation dimension (blue lines) and reward (red line), along with the result of applying the same policy to the real environment (black lines). The model's uncertainty is visualized by plotting lines the maximum and minimum predictions at each time step. The model and policy are specified by passing directories containing configuration files for each; they can be trained independently. The following gif shows an example of 200 steps of pre-trained MBPO policy on Inverted Pendulum environment.

    Example of Visualizer

  • DatasetEvaluator: Loads a pre-trained model and a dataset (can be loaded from separate directories), and computes predictions of the model for each output dimension. The evaluator then creates a scatter plot for each dimension comparing the ground truth output vs. the model's prediction. If the model is an ensemble, the plot shows the mean prediction as well as the individual predictions of each ensemble member.

    Example of DatasetEvaluator

  • FineTuner: Can be used to train a model on a dataset produced by a given agent/controller. The model and agent can be loaded from separate directories, and the fine tuner will roll the environment for some number of steps using actions obtained from the controller. The final model and dataset will then be saved under directory "model_dir/diagnostics/subdir", where subdir is provided by the user.

  • True Dynamics Multi-CPU Controller: This script can run a trajectory optimizer agent on the true environment using Python's multiprocessing. Each environment runs in its own CPU, which can significantly speed up costly sampling algorithm such as CEM. The controller will also save a video if the render argument is passed. Below is an example on HalfCheetah-v2 using CEM for trajectory optimization. To specify the environment, follow the single string syntax described here.

    Control Half-Cheetah True Dynamics

  • TrainingBrowser: This script launches a lightweight training browser for plotting rewards obtained after training runs (as long as the runs use our logger). The browser allows aggregating multiple runs and displaying mean/std, and also lets the user save the image to hard drive. The legend and axes labels can be edited in the pane at the bottom left. Requires installing PyQt5. Thanks to a3ahmad for the contribution!

    Training Browser Example

Note that, except for the training browser, all the tools above require Mujoco installation and are specific to models of type OneDimTransitionRewardModel. We are planning to extend this in the future; if you have useful suggestions don't hesitate to raise an issue or submit a pull request!

Advanced Examples

MBRL-Lib can be used for many different research projects in the subject area. Below are some community-contributed examples:


Please check out our documentation and don't hesitate to raise issues or contribute if anything is unclear!


mbrl is released under the MIT license. See LICENSE for additional details about it. See also our Terms of Use and Privacy Policy.


If you use this project in your research, please cite:

  author  = {Luis Pineda and Brandon Amos and Amy Zhang and Nathan O. Lambert and Roberto Calandra},
  journal = {Arxiv},
  title   = {MBRL-Lib: A Modular Library for Model-based Reinforcement Learning},
  year    = {2021},
  url     = {},