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Custom Audiences

Custom audiences let you target specific groups of users beyond the regular targeting options. Custom audiences can be configured for any experiment through the experimenter UI:

custom audience screenshot

They are:

  • Optional - Don't use them unless you need to limit the experiment to specific group of users.
  • Specific to a particular application (Not all audiences can target all applications)
  • Evaluated on clients via an expression language (JEXL)

How to add a new custom audience

Create a PR against targeting/ that adds a new JEXL expression. There is a recorded session showing 2 examples of adding custom targeting to demoonstrate where to start.

Request review from a console core team member. It should be available in the Experimenter UI a few minutes after the PR has merged.

If you're an iOS or a Android developer check the following instructions for how to add new client-side targeting attributes:


New custom audiences should be tested by the core Nimbus team before they are used in production. This could involve any or all of the following:

  • Test the whole JEXL expression on each application/device it is intended to run on.
  • Ask QA to help verify it by creating a dummy experiment.
  • Launch an A/A in nightly to see if real users enroll correctly