Working with Features

The nimbus-cli provides features to download experiments from Remote Settings. However, sometimes you wish to do some exploratory testing of a feature without going through the experimenter interface.

test-feature

The test-feature command allows you to specify a feature-id and one or more JSON files that correspond to the feature configuration for that feature: i.e. to exercise a feature.

e.g.

nimbus-cli --app firefox_ios --channel developer test-feature messaging my-treatment.json my-control.json

For the above nimbus-cli will generate an experiment which will enroll in to the given app and channel for the messaging, with two branches: my-treatment and my-control. It will enroll in the first of the branches, i.e. my-treatment.

The other branches are available to enroll using the Experiments screen available through the app's UI.

By default, the app's feature manifest will be downloaded and used to validate each feature configuration. This can be overridden with the --no-validate option.

features

The features command accepts an experiment and branch, and outputs the feature configuration from that branch.

nimbus-cli --app fenix --channel developer features release-android-onboarding-redesign --branch treatment-a

will output the JSON as specified by the branch:

{
  "enabled": true
}

You can specify an optional --output FILE to write it to disk.

nimbus-cli --app fenix --channel developer features release-android-onboarding-redesign --branch treatment-a --output new-onboarding.json

tip

Wherever a JSON file is specified, you can use JSON or YAML, just by changing the file name.

nimbus-cli --app fenix --channel developer features release-android-onboarding-redesign --branch treatment-a --output new-onboarding.yaml

This can be useful to add the winning branch configuration to the feature defaults in the feature manifest in the app's codebase, to make the change permanent.

By default, the features command outputs the experimental feature configurations for all features involved in the experiment. At the moment, this is always one.

When more than one feature per branch is available, the output will be of the format:

{
  "$feature1_id": {},
  "$feature2_id": {},
}

You can force a single feature experiment to use this format with the --multi flag:

nimbus-cli --app fenix --channel developer features release-android-onboarding-redesign --branch treatment-a --multi

gives this output:

{
  "juno-onboarding": {
    "enabled": true
  }
}

Alternatively, if you only want one feature of many, you can specify the feature id with the --feature parameter.

nimbus-cli --app fenix --channel developer features release-android-onboarding-redesign --branch treatment-a --feature juno-onboarding

If you are writing automated tooling on top of the features command, it is strongly recommended you use one of these options to get consistent output.