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OpenFeature Logo

OpenFeature Rust SDK

Specification Release
Crates.io Min rust version Repo status

OpenFeature is an open standard that provides a vendor-agnostic, community-driven API for feature flagging that works with your favorite feature flag management tool.

🚀 Quick start


This package was built with Rust version 1.70.0. Earlier versions might work, but is not guaranteed.


Add the following content to the Cargo.toml file:

open-feature = "0.2.3"


async fn example() -> Result<(), Error> {
    // Acquire an OpenFeature API instance.
    // Note the `await` call here because asynchronous lock is used to
    // guarantee thread safety.
    let mut api = OpenFeature::singleton_mut().await;

    // Configure a provider.
    // By default [`NoOpProvider`] is used.

    // create a client
    let client = api.get_client();

    // get a bool flag value
    let is_feature_enabled = client
        .get_bool_value("v2_enabled", None, None)


Note that the default NoOpProvider always returns Err for any given input.

Extended Example

async fn extended_example() {
    // Acquire an OpenFeature API instance.
    let mut api = OpenFeature::singleton_mut().await;

    // Set the default (unnamed) provider.

    // Create an unnamed client.
    let client = api.create_client();

    // Create an evaluation context.
    // It supports types mentioned in the specification.
    let evaluation_context = EvaluationContext::default()
        .with_custom_field("bool_key", true)
        .with_custom_field("int_key", 100)
        .with_custom_field("float_key", 3.14)
        .with_custom_field("string_key", "Hello".to_string())
        .with_custom_field("datetime_key", time::OffsetDateTime::now_utc())
        .with_custom_field("another_struct_key", Arc::new(MyStruct::default()))

    // This function returns a `Result`.
    // You can process it with functions provided by std.
    let is_feature_enabled = client
        .get_bool_value("SomeFlagEnabled", Some(&evaluation_context), None)

    if is_feature_enabled {
        // Let's get evaluation details.
        let _result = client
            .get_int_details("key", Some(&evaluation_context), None)

Getting a Struct from a Provider

It is possible to extract a struct from the provider. Internally, this SDK defines a type StructValue to store any structure value. The client.get_struct_value() functions takes a type parameter T. It will try to parse StructValue resolved by the provider to T, as long as T implements trait TryFrom<StructValue>.

You can pass in a type that satisfies this trait bound. When the conversion fails, it returns an Err with EvaluationReason::TypeMismatch.

API Reference

See here for the API docs.

🌟 Features

Status Features Description
✅ Providers Integrate with a commercial, open source, or in-house feature management tool.
✅ Targeting Contextually-aware flag evaluation using evaluation context.
❌ Hooks Add functionality to various stages of the flag evaluation life-cycle.
❌ Logging Integrate with popular logging packages.
✅ Named clients Utilize multiple providers in a single application.
❌ Eventing React to state changes in the provider or flag management system.
✅ Shutdown Gracefully clean up a provider during application shutdown.
❌ Extending Extend OpenFeature with custom providers and hooks.

Implemented: ✅ | In-progress: ⚠️ | Not implemented yet: ❌


Providers are an abstraction between a flag management system and the OpenFeature SDK. Look here for a complete list of available providers. If the provider you're looking for hasn't been created yet, see the develop a provider section to learn how to build it yourself.

Once you've added a provider as a dependency, it can be registered with OpenFeature like this:

// Set the default feature provider. Please replace the `NoOpProvider` with the one you want.
// If you do not do that, [`NoOpProvider`] will be used by default.
// [`NoOpProvider`] always returns `Err` despite any input. You can use functions like 
// `unwrap_or()` to specify default values.
// If you set a new provider after creating some clients, the existing clients will pick up
// the new provider you just set.
// You must `await` it to let the provider's initialization to finish.
let mut api = OpenFeature::singleton_mut().await;

In some situations, it may be beneficial to register multiple providers in the same application. This is possible using named clients, which is covered in more detail below.


Sometimes, the value of a flag must consider some dynamic criteria about the application or user, such as the user's location, IP, email address, or the server's location. In OpenFeature, we refer to this as targeting. If the flag management system you're using supports targeting, you can provide the input data using the evaluation context.

// Create a global evaluation context and set it into the API.
// Note that this is optional. By default it uses an empty one.
let mut api = OpenFeature::singleton_mut().await;

// Set client level evaluation context.
// It will overwrite the global one for the existing keys.
let mut client = api.create_client();

// Pass evaluation context in evaluation functions.
// This one will overwrite the globla evaluation context and 
// the client level one.
client.get_int_value("flag", Some(&evaluation_context), None);


Hooks are not yet available in the Rust SDK.


Logging customization is not yet available in the Rust SDK.

Named clients

Clients can be given a name. A name is a logical identifier that can be used to associate clients with a particular provider. If a name has no associated provider, the global provider is used.

// Create a named provider and bind it.
api.set_named_provider("named", NoOpProvider::default()).await;

// This named client will use the feature provider bound to this name.
let client = api.create_named_client("named");

assert_eq!(client.get_int_value("key", None, None).await.unwrap(), 42);


Events are not yet available in the Rust SDK.


The OpenFeature API provides a close function to perform a cleanup of all registered providers. This should only be called when your application is in the process of shutting down.

// This will clean all the registered providers and invoke their `shutdown()` function.
let api = OpenFeature::singleton_mut().await;


Develop a provider

To develop a provider, you need to create a new project and include the OpenFeature SDK as a dependency. This can be a new repository or included in the existing contrib repository available under the OpenFeature organization. You’ll then need to write the provider by implementing the FeatureProvider interface exported by the OpenFeature SDK.

Check the source of NoOpProvider for an example.

Built a new provider? Let us know so we can add it to the docs!

Develop a hook

Hooks are not yet available in the Rust SDK.

⭐️ Support the project

🤝 Contributing

Interested in contributing? Great, we'd love your help! To get started, take a look at the CONTRIBUTING guide.

Thanks to everyone who has already contributed

Pictures of the folks who have contributed to the project

Made with contrib.rocks.


~93K SLoC