Getting Started

Welcome! In this chapter, we give a quick overview of Oríon’s main features and how it can help you streamline your machine learning workflow whether you are a researcher or engineer.

Oríon is a black box function optimization library with a key focus on usability and integrability for its users. For example, as a machine learning engineer, you can integrate Oríon to your existing ML workflow to handle reliably the hyperparameter optimization and tuning phase. As a ML researcher, you can use Oríon to tune your models but also integrate your own algorithms to Oríon to serve as an efficient optimization engine and compare with other algorithms in the same context and conditions.

Conversely, Oríon does not aim to be a machine learning framework or pipeline, or an automatic machine learning product. Oríon focuses essentially on black box optimization. However, we do encourage developers to integrate Oríon into that kind of systems as a component and we will do our best to help you if you’re interested.

Before continuing the overview, we assume that you have a basic understanding of machine learning concepts. You may also want to install Oríon on your machine and configure it for a database before continuing. Please refer to our installation instructions and database setup.

We also made a presentation if you prefer going along with narrated content!


The core value of Oríon is to be non-intrusive. As such, we made it very easy to integrate it in your machine learning environment. Suppose you’re normally executing ./ --lr=0.1, with lr controlling your learning rate.

The only modification you have to do is to call orion.client.report_objective() at the end of your script to report the results of the hyper-parameter optimization with the objective to minimize as the parameter.

We made a tutorial to guide you through those steps.

Python API

Oríon can also be run from Python using our Python API, making it easy to integrate it in any machine learning workflow or product. A detailed overview of this feature is available in Optimize and Storage.


To actually optimize the hyper-parameters, we use Oríon hunt command to start the black-box optimization process.

For the previous example, we would run

$ orion hunt -n <experiment name> --lr~'loguniform(1e-5, 1.0)'

This is going to start the optimization process using the default optimization algorithm and sample the values for the lr hyper-parameter in a log uniform distribution between 0.00001 et 1.0. Each trial will be stored in the database that you configured during the installation process (which can be in-memory, a file, or a local or remote MongoDB instance).

Additionally, the experiments are versioned – think of it as a git for scientific experimentation – enabling you to keep track of all your trials with their parameters. This guarantees that you can reproduce or trace back the steps in your work for free.

You can fine-tune the distribution and algorithm with many options either with more arguments or by using a configuration file. Learn more at Optimize.

Scaling up

Oríon is built to operate in parallel environments and is natively asynchronous; it runs efficiently whether you execute it on your laptop or in a computing farm with thousands of processors.

Moreover, adding more workers is as easy as executing the $ orion hunt command for each extra worker needed. Indeed, Oríon doesn’t uses a master / worker approach. The synchronization point is the database: each worker will separately generate a new trial based on the state of the experiment stored in the database.

Make sure to visit Parallel Workers to learn more about it and check out the tutorial to run Oríon in HPC environments.

Search Space

The search space is defined by priors for each hyperparameter to optimize. In the snippet earlier, we used the loguniform prior. Oríon supports a vast range of search spaces, including almost all the distributions from scipy out of the box. You can define them either directly in the command line (as shown previously) or in a configuration file:

lr: 'orion~loguniform(1e-5, 1.0)'

And then use it with:

$ orion hunt -n <experiment name> --config config.yaml

Make sure to visit Search Space for an exhaustive list of priors and their parameters.


Oríon supports the latest established hyperparameter algorithms out of the box such as Random Search, ASHA, TPE, and Hyperband; making it easy to switch between them or create benchmarks. Each algorithm is fully configurable through the configuration file.

You can also bring your own algorithms to Oríon with its plugin system, where you can compare it against other algorithms using the same framework and dataset. It also enables you to easily share and publish your algorithm to other members of the community.

Make sure to checkout this presentation for a quick overview of each algorithm and to visit Algorithms to learn about the algorithms and get recommendations about their use cases.


Oríon offers different ways to get information about your experiments and trials.

  • $ orion list gives an overview of all the experiments.
  • $ orion status gives an overview of trials for experiments.
  • $ orion info gives a detailed description of a given experiment such as priors and best trials.

Each command is described in detail in Monitoring.

If you want a more fine grained approach, you can always query the database directly or via Oríon’s python API. Check out Storage for more information.

Next steps

It’s worth to take a look at the configuration system to learn more about how to make the most out of Oríon and define precise behaviors for your algorithms and experiments. Oríon uses a configuration agnostic approach where you can use any configuration file format you’re comfortable with.

Explore the User Manual, Oríon is simple from the outside but is feature rich! We also have a few tutorials available (e.g., Scikit-learn, PyTorch MNIST). If you’re a researcher or developer you might be interested to contribute or develop your own algorithms plugins!