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Version: 1.1

Getting started


Hydra is an open-source Python framework that simplifies the development of research and other complex applications. The key feature is the ability to dynamically create a hierarchical configuration by composition and override it through config files and the command line. The name Hydra comes from its ability to run multiple similar jobs - much like a Hydra with multiple heads.

Key features:#

  • Hierarchical configuration composable from multiple sources
  • Configuration can be specified or overridden from the command line
  • Dynamic command line tab completion
  • Run your application locally or launch it to run remotely
  • Run multiple jobs with different arguments with a single command


Hydra supports Linux, Mac and Windows.
Use the version switcher in the top bar to switch between documentation versions.

VersionRelease notesPython Versions
โ–บ1.1 (Stable)Release notes3.6 - 3.9
1.0Release notes3.6 - 3.8
0.11Release notes2.7, 3.5 - 3.8

Quick start guide#

This guide will show you some of the most important features of Hydra. Read the tutorial to gain a deeper understanding.


pip install hydra-core --upgrade

Basic example#


db:  driver: mysql  user: omry  pass: secret

import hydrafrom omegaconf import DictConfig, OmegaConf
@hydra.main(config_path="conf", config_name="config")def my_app(cfg : DictConfig) -> None:    print(OmegaConf.to_yaml(cfg))
if __name__ == "__main__":    my_app()

You can learn more about OmegaConf here later.

config.yaml is loaded automatically when you run your application

$ python my_app.pydb:  driver: mysql  pass: secret  user: omry

You can override values in the loaded config from the command line:

$ python db.user=root db.pass=1234db:  driver: mysql  user: root  pass: 1234

Composition example#

You may want to alternate between two different databases. To support this create a config group named db, and place one config file for each alternative inside: The directory structure of our application now looks like:

โ”œโ”€โ”€ confโ”‚ย ย  โ”œโ”€โ”€ config.yamlโ”‚ย ย  โ”œโ”€โ”€ dbโ”‚ย ย  โ”‚ย ย  โ”œโ”€โ”€ mysql.yamlโ”‚ย ย  โ”‚ย ย  โ””โ”€โ”€ postgresql.yamlโ”‚ย ย  โ””โ”€โ”€ __init__.pyโ””โ”€โ”€

Here is the new config:

defaults:  - db: mysql

defaults is a special directive telling Hydra to use db/mysql.yaml when composing the configuration object. The resulting cfg object is a composition of configs from defaults with configs specified in your config.yaml.

You can now choose which database configuration to use and override values from the command line:

$ python db=postgresql db.timeout=20db:  driver: postgresql  pass: drowssap  timeout: 20  user: postgres_user

You can have as many config groups as you need.


You can run your function multiple times with different configuration easily with the --multirun|-m flag.

$ python --multirun db=mysql,postgresql[HYDRA] Sweep output dir : multirun/2020-01-09/01-16-29[HYDRA] Launching 2 jobs locally[HYDRA]        #0 : db=mysqldb:  driver: mysql  pass: secret  user: omry
[HYDRA]        #1 : db=postgresqldb:  driver: postgresql  pass: drowssap  timeout: 10  user: postgres_user

There is a whole lot more to Hydra. Read the tutorial to learn more.

Other stuff#


Ask questions in the chat or StackOverflow (Use the tag #fb-hydra):

Follow Hydra on Twitter and Facebook:

Citing Hydra#

If you use Hydra in your research please use the following BibTeX entry:

@Misc{Yadan2019Hydra,  author =       {Omry Yadan},  title =        {Hydra - A framework for elegantly configuring complex applications},  howpublished = {Github},  year =         {2019},  url =          {}}