Eppo's SDKs

Eppo's SDKs all follow a similar architecture and interface. Whether you are using Eppo for feature gates, progressive rollouts, or randomized experiments, you can determine what variant a specific subject (e.g., user) should see with a call like this:

const eppoClient = EppoSdk.getInstance();
const variation = eppoClient.getStringAssignment(
  "<SUBJECT-KEY>",
  "<FLAG-KEY>",
  {
    // Optional map of subject metadata for targeting.
  }
);

Here, SUBJECT-KEY is a unique identifier for the unit on which you are assigning (e.g., user_id) and FLAG-KEY is a unique identifier for the feature of interest (e.g., new_user_onboarding). The optional third argument provides subject-level properties for targeting.

For experimentation use cases, Eppo uses a deterministic hashing function to ensure that the same variant is returned for a given SUBJECT-KEY. This guarantee also holds across different SDKs. That is, experiment assignments from a server SDK will be consistent with experiment assignments from a client SDK for the same SUBJECT-KEY.

Before using the Eppo SDK, you'll need to generate an SDK key and create a logging callback function.

You can read more about our specific SDKs here: