> For the complete documentation index, see [llms.txt](https://developer.harness.io/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://developer.harness.io/feature-management-experimentation/use-fme/feature-management/setup/fallback-treatment.md). # Fallback treatment ### Overview Fallback treatments are returned by an FME SDK when your application requests a treatment for a feature flag but the SDK cannot determine the value through normal evaluation. {% hint style="info" %} This behavior is defined in the SDK itself and is not configured through the Harness FME UI. {% endhint %} Fallback treatments are applicable in the following scenarios: * The SDK cannot connect to Harness services (for example, due to network failure or missing attributes) * A feature flag or segment evaluation times out * The flag evaluation cannot be fetched or cached locally * The evaluation context is incomplete or invalid for targeting * An unexpected error occurs during evaluation ### How fallback treatments differ from control treatment The [control treatment](/feature-management-experimentation/use-fme/feature-management/setup/control-treatment.md) is a reserved treatment in FME that the SDK returns in cases such as missing flag definitions, initialization is not compete, unsupported targeting rules, or unexpected exceptions. The fallback treatment, on the other hand, is customizable. You choose what the SDK should return if evaluation cannot be completed (for example, `"off"` or `"old-version"`). Harness recommends providing a fallback treatment when calling the SDK to ensure a predictable user experience if Harness is unavailable, and using low-risk values (like `"off"`) as fallbacks to reduce exposure risk. ### Global vs. flag-level fallback treatments Fallback treatments can be defined **globally** for the entire SDK or **per flag** for more granular control: * **Global fallback**: Returned whenever any flag cannot be evaluated, unless a flag-level fallback is defined. * **Flag-level fallback**: Overrides the global fallback for that specific flag, taking precedence when both are defined. This allows you to customize behavior for individual flags without affecting the global default. For example: ```java // Global fallback treatment FallbackTreatmentsConfiguration fallbackTreatmentsConfiguration = new FallbackTreatmentsConfiguration( new FallbackTreatment("on-fallback", "{\"prop1\":\"val1\"}"), null ); SplitClientConfig config = SplitClientConfig.builder() .fallbackTreatments(fallbackTreatmentsConfiguration) .build(); SplitFactory factory = SplitFactoryBuilder.build("YOUR_API_KEY", config); SplitClient client = factory.client(); // Flag-level fallback treatment // Overrides the global fallback for the specified flag FallbackTreatmentsConfiguration flagFallbackConfig = new FallbackTreatmentsConfiguration( null, new HashMap() {{ put("FEATURE_FLAG_NAME", new FallbackTreatment("off", "{\"prop2\":\"val2\"}")); }} ); SplitClientConfig clientConfigWithFlagFallback = SplitClientConfig.builder() .fallbackTreatments(flagFallbackConfig) .build(); SplitFactory factoryWithFlagFallback = SplitFactoryBuilder.build("YOUR_API_KEY", clientConfigWithFlagFallback); SplitClient clientWithFlagFallback = factoryWithFlagFallback.client(); ``` ### Supported SDKs for fallback treatments Select an SDK to configure fallback treatments for both client and server applications. | Android | iOS | Browser | Flutter | JavaScript | React | React Native | Java | Python | Ruby | .NET | Node.js | Go | | ------- | ------ | ------- | ------- | ---------- | ------ | ------------ | ------- | ------- | ------ | ------- | -------- | ------ | | 5.4.1+ | 3.4.0+ | 1.6.0+ | 1.2.0+ | 11.8.0+ | 2.6.0+ | 1.5.0+ | 4.18.0+ | 10.5.1+ | 8.9.0+ | 7.12.0+ | 11.8.0 + | 6.9.0+ |
Android SDK/pages/8AF59NZ2aqPq17XR8ugB#configure-fallback-treatments
iOS SDK/pages/7GUS0j7lBbffwUUTAgvq#configure-fallback-treatments
Browser SDK/pages/1cFJyht3YZXhzQfQQwLe#configure-fallback-treatments
Flutter Plugin/pages/snGwWXajHlfJW7GDuFNF#configure-fallback-treatments
JavaScript SDK/pages/2W8f1cXqxHpZb3xLL5je#configure-fallback-treatments
React SDK/pages/avzO8zntoEWOK5ZVqkA3#configure-fallback-treatments
React Native SDK/pages/foy1cK0LEZ2lp8QguIuf#configure-fallback-treatments
Java SDK/pages/uwrbv211wAgmTIdyenQD#configure-fallback-treatments
Python SDKPython SDK/pages/sLjI7D2F7J7Fvg1ZKE9g#configure-fallback-treatments
Ruby SDKRuby SDK/pages/ZRyRRi2ra4rGRlie7iRQ#configure-fallback-treatments
.NET SDK/pages/AogFQGSeilYEy4E1M6nj#configure-fallback-treatments
Node.js SDK/pages/Ffpw4KXywnonGdBt79yQ#configure-fallback-treatments
Go SDK/pages/9S5EdLJQSGskpM0SkLxH#configure-fallback-treatments