Run experiments

Version:

The justtrack SDK lets you run server-side experiments (A/B tests) in your app. Experiments are configured on the justtrack backend, which assigns each user to a variant. The SDK fetches these assignments and gives you typed access to config values so you can branch your app logic accordingly.

In this guide, you'll learn to:

• Fetch experiment assignments from the server
• Activate experiments to confirm user enrollment
• Read experiment values in your app
• Configure the fetch interval

Fetch experiment assignments

Call fetch to pull the latest experiment assignments from the justtrack backend. The SDK caches assignments locally, so subsequent reads are fast and offline-safe.

For example, on app launch you'd fetch the latest assignments so your UI reflects the user's assigned variants:

Android

sdk.remoteConfig.fetch().await()

iOS

try await sdk.remoteConfig.fetch()

Unity

IRemoteConfig remoteConfig = JustTrackSDK.GetRemoteConfig();
remoteConfig.Fetch(
    () => { Debug.Log("Fetch succeeded"); },
    (error) => { Debug.LogError("Fetch failed: " + error); }
);

React Native

await JustTrackSdk.remoteConfig.fetch();

info

The SDK respects a minimum fetch interval to avoid excessive network requests. If you call fetch again before the interval has elapsed, the SDK returns the cached assignments without contacting the server. See Configure the fetch interval for details.

Activate experiments

Fetching assignments downloads them to the device, but doesn't tell the backend the user was actually exposed to the experiment. Call activate to confirm enrollment — only activated experiments count toward your experiment results in the dashboard.

For example, after the user sees a new onboarding flow, activate that experiment so justtrack records the exposure:

Android

val assignments = sdk.remoteConfig.getAll()
val experimentIds = assignments?.map { it.experimentId } ?: emptyList()
sdk.remoteConfig.activate(experimentIds).await()

iOS

let assignments = sdk.remoteConfig.allAssignments
let experimentIds = assignments.map { $0.experimentId }
try await sdk.remoteConfig.activate(experimentIds: experimentIds)

Unity

IRemoteConfig remoteConfig = JustTrackSDK.GetRemoteConfig();
Assignment[] assignments = remoteConfig.GetAll();
string[] experimentIds = assignments.Select(a => a.ExperimentId).ToArray();
remoteConfig.Activate(experimentIds,
    () => { Debug.Log("Activation succeeded"); },
    (error) => { Debug.LogError("Activation failed: " + error); }
);

React Native

const assignments = JustTrackSdk.remoteConfig.getAll();
const experimentIds = assignments.map(a => a.experimentId);
await JustTrackSdk.remoteConfig.activate(experimentIds);

Fetch and activate in one step

If you want to fetch the latest assignments and immediately confirm enrollment for all of them, use fetchAndActivate. This is useful at app startup when you want to get everything ready in a single call:

Android

sdk.remoteConfig.fetchAndActivate().await()

iOS

try await sdk.remoteConfig.fetchAndActivate()

Unity

IRemoteConfig remoteConfig = JustTrackSDK.GetRemoteConfig();
remoteConfig.FetchAndActivate(
    () => { Debug.Log("Fetch and activate succeeded"); },
    (error) => { Debug.LogError("Fetch and activate failed: " + error); }
);

React Native

await JustTrackSdk.remoteConfig.fetchAndActivate();

Read experiment values

After fetching, you can read experiment values from the local cache. Values are available immediately and don't require a network call.

Get all assignments

To list every experiment the user is enrolled in, call getAll. Each assignment contains the config key, its value, the experiment ID, and whether it's still pending activation.

This is useful for building a debug screen or iterating over all active experiments:

Android

val assignments = sdk.remoteConfig.getAll()
assignments?.forEach { assignment ->
    Log.d("Experiment", "${assignment.configKey} = ${assignment.configValue}")
}

iOS

let assignments = sdk.remoteConfig.allAssignments
for assignment in assignments {
    print("\(assignment.configKey) = \(assignment.configValue)")
}

Unity

IRemoteConfig remoteConfig = JustTrackSDK.GetRemoteConfig();
Assignment[] assignments = remoteConfig.GetAll();
foreach (Assignment assignment in assignments)
{
    Debug.Log($"{assignment.ConfigKey} = {assignment.ConfigValue}");
}

React Native

const assignments = JustTrackSdk.remoteConfig.getAll();
assignments.forEach(a => {
    console.log(`${a.configKey} = ${a.configValue}`);
});

Each assignment has the following fields:

Field	Description
configKey	The key you use to look up this value (e.g. "onboarding_variant").
configValue	The raw string value assigned to this user.
experimentId	The unique ID of the experiment this assignment belongs to.
isPending	true if the assignment hasn't been activated yet.

Get a value by config key

To check a specific experiment value, use one of the typed getter methods. For example, to decide which onboarding flow to show:

Android

val variant = sdk.remoteConfig.getString("onboarding_variant")
if (variant == "new_flow") {
    showNewOnboarding()
} else {
    showDefaultOnboarding()
}

iOS

let variant = sdk.remoteConfig.getString(configKey: "onboarding_variant")
if variant == "new_flow" {
    showNewOnboarding()
} else {
    showDefaultOnboarding()
}

Unity

IRemoteConfig remoteConfig = JustTrackSDK.GetRemoteConfig();
string variant = remoteConfig.GetString("onboarding_variant");
if (variant == "new_flow")
{
    ShowNewOnboarding();
}
else
{
    ShowDefaultOnboarding();
}

React Native

const variant = JustTrackSdk.remoteConfig.getString('onboarding_variant');
if (variant === 'new_flow') {
    showNewOnboarding();
} else {
    showDefaultOnboarding();
}

The following typed getters are available:

Type	Android	iOS	Unity	React Native
String	getString()	getString()	GetString()	getString()
Boolean	getBoolean()	getBool()	GetBoolean()	getBoolean()
Integer	getInt()	getInt()	GetInt()	getNumber()
Double	getDouble()	getDouble()	GetDouble()	getNumber()
Long	getLong()	—	GetLong()	—

All getters return null if no assignment exists for the given config key.

Configure the fetch interval

The SDK enforces a minimum interval between server fetches to avoid unnecessary network requests. If you call fetch before the interval has elapsed, the SDK returns cached assignments instead.

The default interval is 24 hours (86,400 seconds).

During development, you can lower this interval to iterate faster:

Android

sdk.remoteConfig.setConfig(JusttrackRemoteConfigSettings(60))

iOS

sdk.remoteConfig.setConfig(JusttrackRemoteConfigSettings(minFetchIntervalInSec: 60))

Unity

IRemoteConfig remoteConfig = JustTrackSDK.GetRemoteConfig();
remoteConfig.SetConfig(new JusttrackRemoteConfigSettings(60));

React Native

JustTrackSdk.remoteConfig.setConfig({ minFetchIntervalInSeconds: 60 });

warning

Keep the default interval in production. Lowering it causes more network requests from every user, which increases load on your app and the justtrack backend.

Example: A/B test your onboarding flow

Here's a complete example that ties everything together. Suppose you've configured an experiment on the justtrack backend with a config key onboarding_variant. Users are assigned either "control" (the existing flow) or "new_flow" (a redesigned experience).

At app startup, fetch and activate the experiment, then branch your logic based on the assigned variant:

Android

// Fetch the latest experiment assignments and activate them
sdk.remoteConfig.fetchAndActivate().await()

// Read the assigned variant
val variant = sdk.remoteConfig.getString("onboarding_variant")

when (variant) {
    "new_flow" -> showNewOnboarding()
    else -> showDefaultOnboarding()
}

iOS

// Fetch the latest experiment assignments and activate them
try await sdk.remoteConfig.fetchAndActivate()

// Read the assigned variant
let variant = sdk.remoteConfig.getString(configKey: "onboarding_variant")

switch variant {
case "new_flow":
    showNewOnboarding()
default:
    showDefaultOnboarding()
}

Unity

IRemoteConfig remoteConfig = JustTrackSDK.GetRemoteConfig();

// Fetch the latest experiment assignments and activate them
remoteConfig.FetchAndActivate(
    () =>
    {
        // Read the assigned variant
        string variant = remoteConfig.GetString("onboarding_variant");

        if (variant == "new_flow")
        {
            ShowNewOnboarding();
        }
        else
        {
            ShowDefaultOnboarding();
        }
    },
    (error) =>
    {
        Debug.LogError("Failed to fetch experiments: " + error);
        // Fall back to the default experience
        ShowDefaultOnboarding();
    }
);

React Native

// Fetch the latest experiment assignments and activate them
await JustTrackSdk.remoteConfig.fetchAndActivate();

// Read the assigned variant
const variant = JustTrackSdk.remoteConfig.getString('onboarding_variant');

if (variant === 'new_flow') {
    showNewOnboarding();
} else {
    showDefaultOnboarding();
}