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OpenFeature Ruby SDK

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Quick start​

MCP Install

Follow the MCP Getting Started guide to quickly set up the OpenFeature MCP server and connect your AI tool.

  • Run this prompt: "Install OpenFeature into this app"

Quick Install:

claude mcp add --transport stdio openfeature npx -y @openfeature/mcp

Requirements​

Supported Ruby VersionOS
Ruby 3.4.xWindows, MacOS, Linux
Ruby 4.0.xWindows, MacOS, Linux

This project supports all Ruby versions in active maintenance per the Ruby maintenance schedule.

Install​

Install the gem and add to the application's Gemfile by executing:

bundle add openfeature-sdk

If bundler is not being used to manage dependencies, install the gem by executing:

gem install openfeature-sdk

Usage​

require 'open_feature/sdk'
require 'json' # For JSON.dump

# API Initialization and configuration

OpenFeature::SDK.configure do |config|
  # your provider of choice, which will be used as the default provider
  config.set_provider(OpenFeature::SDK::Provider::InMemoryProvider.new(
    {
      "flag1" => true,
      "flag2" => 1
    }
  ))
end

# Create a client
client = OpenFeature::SDK.build_client

# fetching boolean value feature flag
bool_value = client.fetch_boolean_value(flag_key: 'boolean_flag', default_value: false)

# a details method is also available for more information about the flag evaluation
# see `ResolutionDetails` for more info
bool_details = client.fetch_boolean_details(flag_key: 'boolean_flag', default_value: false)

# fetching string value feature flag
string_value = client.fetch_string_value(flag_key: 'string_flag', default_value: 'default')

# fetching number value feature flag
float_value = client.fetch_number_value(flag_key: 'number_value', default_value: 1.0)
integer_value = client.fetch_number_value(flag_key: 'number_value', default_value: 1)

# get an object value
object = client.fetch_object_value(flag_key: 'object_value', default_value: { name: 'object'})

Features​

StatusFeaturesDescription
✅ProvidersIntegrate with a commercial, open source, or in-house feature management tool.
✅TargetingContextually-aware flag evaluation using evaluation context.
✅HooksAdd functionality to various stages of the flag evaluation life-cycle.
✅LoggingIntegrate with popular logging packages.
✅DomainsLogically bind clients with providers.
✅EventingReact to state changes in the provider or flag management system.
✅ShutdownGracefully clean up a provider during application shutdown.
✅TrackingAssociate user actions with feature flag evaluations for experimentation.
✅Transaction Context PropagationSet a specific evaluation context for a transaction (e.g. an HTTP request or a thread)
✅ExtendingExtend OpenFeature with custom providers and hooks.
Implemented: ✅ | In-progress: ⚠️ | Not implemented yet: ❌

Providers​

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:

OpenFeature::SDK.configure do |config|
  # your provider of choice, which will be used as the default provider
  config.set_provider(OpenFeature::SDK::Provider::InMemoryProvider.new(
    {
      "v2_enabled" => true,
    }
  ))
end

Blocking Provider Registration​

If you need to ensure that a provider is fully initialized before continuing, you can use set_provider_and_wait:

# Using the SDK directly
begin
  OpenFeature::SDK.set_provider_and_wait(my_provider)
  puts "Provider is ready!"
rescue OpenFeature::SDK::ProviderInitializationError => e
  puts "Provider failed to initialize: #{e.message}"
  puts "Error code: #{e.error_code}"
  # original_error contains the underlying exception that caused the initialization failure
  puts "Original error: #{e.original_error}"
end

# With custom timeout (default is 30 seconds)
OpenFeature::SDK.set_provider_and_wait(my_provider, timeout: 60)

# Domain-specific provider
OpenFeature::SDK.set_provider_and_wait(my_provider, domain: "feature-flags")

# Via configuration block
OpenFeature::SDK.configure do |config|
  begin
    config.set_provider_and_wait(my_provider)
  rescue OpenFeature::SDK::ProviderInitializationError => e
    # Handle initialization failure
  end
end

The set_provider_and_wait method:

  • Waits for the provider's init method to complete successfully
  • Raises ProviderInitializationError if initialization fails or times out
  • Provides access to the provider instance, error code, and original exception for debugging
  • The original_error field contains the underlying exception that caused the initialization failure
  • Uses the same thread-safe provider switching as set_provider

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

Targeting​

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.

OpenFeature::SDK.configure do |config|
  # you can set a global evaluation context here
  config.evaluation_context = OpenFeature::SDK::EvaluationContext.new("host" => "myhost.com")
end

# Evaluation context can be set on a client as well
client_with_context = OpenFeature::SDK.build_client(
  evaluation_context: OpenFeature::SDK::EvaluationContext.new("controller_name" => "admin")
)

# Invocation evaluation context can also be passed in during flag evaluation.
# During flag evaluation, invocation context takes precedence over client context
# which takes precedence over API (aka global) context.
bool_value = client.fetch_boolean_value(
  flag_key: 'boolean_flag',
  default_value: false,
  evaluation_context: OpenFeature::SDK::EvaluationContext.new("is_friday" => true)
)

Hooks​

Hooks allow for custom logic to be added at well-defined points of the flag evaluation life-cycle. Look here for a complete list of available hooks. If the hook you're looking for hasn't been created yet, see the develop a hook section to learn how to build it yourself.

Hooks can be registered at the global, client, or flag invocation level.

# Define a hook
class MyHook
  include OpenFeature::SDK::Hooks::Hook

  def before(hook_context:, hints:)
    puts "Evaluating flag: #{hook_context.flag_key}"
    nil
  end

  def after(hook_context:, evaluation_details:, hints:)
    puts "Flag #{hook_context.flag_key} evaluated to: #{evaluation_details.value}"
  end

  def error(hook_context:, exception:, hints:)
    puts "Error evaluating #{hook_context.flag_key}: #{exception.message}"
  end

  def finally(hook_context:, evaluation_details:, hints:)
    puts "Evaluation complete for #{hook_context.flag_key}"
  end
end

# Register at the API (global) level
OpenFeature::SDK.hooks << MyHook.new

# Register at the client level
client = OpenFeature::SDK.build_client
client.hooks << MyHook.new

# Register at the invocation level
client.fetch_boolean_value(
  flag_key: "my-flag",
  default_value: false,
  hooks: [MyHook.new]
)

Logging​

The SDK includes a built-in LoggingHook that provides structured log output for flag evaluations. It logs at the before, after, and error stages of the hook lifecycle.

# Use the SDK's default logger (from Configuration)
OpenFeature::SDK.hooks << OpenFeature::SDK::Hooks::LoggingHook.new

# Or provide your own logger
logger = Logger.new($stdout)
OpenFeature::SDK.hooks << OpenFeature::SDK::Hooks::LoggingHook.new(logger: logger)

# Optionally include evaluation context in log output
OpenFeature::SDK.hooks << OpenFeature::SDK::Hooks::LoggingHook.new(
  logger: logger,
  include_evaluation_context: true
)

Log output uses a structured key=value format:

  • before (DEBUG): stage=before domain=my-domain provider_name=my-provider flag_key=my-flag default_value=false
  • after (DEBUG): includes reason, variant, and value
  • error (ERROR): includes error_code and error_message

Domains​

Clients can be assigned to a domain. A domain is a logical identifier which can be used to associate clients with a particular provider. If a domain has no associated provider, the default provider is used.

OpenFeature::SDK.configure do |config|
  config.set_provider(OpenFeature::SDK::Provider::NoOpProvider.new, domain: "legacy_flags")
end

# Create a client for a different domain, this will use the provider assigned to that domain
legacy_flag_client = OpenFeature::SDK.build_client(domain: "legacy_flags")

Eventing​

Events allow you to react to state changes in the provider or underlying flag management system, such as flag definition changes, provider readiness, or error conditions. Initialization events (PROVIDER_READY on success, PROVIDER_ERROR on failure) are dispatched for every provider. Some providers support additional events, such as PROVIDER_CONFIGURATION_CHANGED.

Please refer to the documentation of the provider you're using to see what events are supported.

# Register event handlers at the API (global) level
ready_handler = ->(event_details) do
  puts "Provider #{event_details[:provider].metadata.name} is ready!"
end

OpenFeature::SDK.add_handler(OpenFeature::SDK::ProviderEvent::PROVIDER_READY, ready_handler)

# The SDK automatically emits lifecycle events. Providers can emit additional spontaneous events
# using the EventEmitter mixin to signal internal state changes like configuration updates.
class MyEventAwareProvider
  include OpenFeature::SDK::Provider::EventEmitter

  def init(evaluation_context)
    # Start background process to monitor for configuration changes
    # Note: SDK automatically emits PROVIDER_READY when init completes successfully
    start_background_process
  end

  def start_background_process
    Thread.new do
      # Monitor for configuration changes and emit events when they occur
      if configuration_changed?
        emit_event(
          OpenFeature::SDK::ProviderEvent::PROVIDER_CONFIGURATION_CHANGED,
          message: "Flag configuration updated"
        )
      end
    end
  end
end

# Remove specific handlers when no longer needed
OpenFeature::SDK.remove_handler(OpenFeature::SDK::ProviderEvent::PROVIDER_READY, ready_handler)

Shutdown​

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

# Shut down all registered providers and clear state
OpenFeature::SDK.shutdown

Individual providers can implement a shutdown method to perform cleanup:

class MyProvider
  def shutdown
    # Perform any shutdown/reclamation steps with flag management system here
  end
end

Tracking​

The tracking API allows you to use OpenFeature abstractions and objects to associate user actions with feature flag evaluations. This is essential for robust experimentation powered by feature flags. For example, a flag enhancing the appearance of a UI component might drive user engagement to a new feature; to test this hypothesis, telemetry collected by a hook or provider can be associated with telemetry reported in the client's track function.

client = OpenFeature::SDK.build_client

# Simple tracking event
client.track("checkout_completed")

# With evaluation context
client.track(
  "purchase",
  evaluation_context: OpenFeature::SDK::EvaluationContext.new(targeting_key: "user-123")
)

# With tracking event details (optional numeric value + custom fields)
details = OpenFeature::SDK::TrackingEventDetails.new(
  value: 99.99,
  plan: "premium",
  currency: "USD"
)
client.track("subscription", tracking_event_details: details)

Note that some providers may not support tracking; if the provider does not implement a track method, the call is a no-op. Check the documentation for your provider for more information.

Transaction Context Propagation​

Transaction context is a container for transaction-specific evaluation context (e.g. user id, user agent, IP). Transaction context can be set where specific data is available (e.g. an auth service or request handler) and by using the transaction context propagator it will automatically be applied to all flag evaluations within a transaction (e.g. a request or thread).

The SDK ships with a ThreadLocalTransactionContextPropagator that stores context in Thread.current:

# Set up the propagator
OpenFeature::SDK.set_transaction_context_propagator(
  OpenFeature::SDK::ThreadLocalTransactionContextPropagator.new
)

# Set transaction context (e.g. in a request middleware)
OpenFeature::SDK.set_transaction_context(
  OpenFeature::SDK::EvaluationContext.new(targeting_key: "user-123", "email" => "user@example.com")
)

# Transaction context is automatically merged during flag evaluation.
# Merge precedence: invocation > client > transaction > API (global)
client = OpenFeature::SDK.build_client
client.fetch_boolean_value(flag_key: "my-flag", default_value: false)

You can implement a custom propagator by including the TransactionContextPropagator module:

class MyRequestScopedPropagator
  include OpenFeature::SDK::TransactionContextPropagator

  def set_transaction_context(evaluation_context)
    # Store context in your request-scoped storage
    RequestStore[:openfeature_context] = evaluation_context
  end

  def get_transaction_context
    RequestStore[:openfeature_context]
  end
end

Extending​

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 Provider duck.

class MyProvider
  def init
    # Perform any initialization steps with flag management system here
    # Return value is ignored
    # **Note** The OpenFeature spec defines a lifecycle method called `initialize` to be called when a new provider is set.
    # To avoid conflicting with the Ruby `initialize` method, this method should be named `init` when creating a provider.
  end

  def shutdown
    # Perform any shutdown/reclamation steps with flag management system here
    # Return value is ignored
  end

  def fetch_boolean_value(flag_key:, default_value:, evaluation_context: nil)
    # Retrieve a boolean value from provider source
  end

  def fetch_string_value(flag_key:, default_value:, evaluation_context: nil)
    # Retrieve a string value from provider source
  end

  def fetch_number_value(flag_key:, default_value:, evaluation_context: nil)
    # Retrieve a numeric value from provider source
  end

  def fetch_integer_value(flag_key:, default_value:, evaluation_context: nil)
    # Retrieve a integer value from provider source
  end

  def fetch_float_value(flag_key:, default_value:, evaluation_context: nil)
    # Retrieve a float value from provider source
  end

  def fetch_object_value(flag_key:, default_value:, evaluation_context: nil)
    # Retrieve a hash value from provider source
  end

  # Optional: implement tracking support (spec 6.1.4)
  # If not defined, Client#track is a no-op
  def track(tracking_event_name, evaluation_context:, tracking_event_details:)
    # Record a tracking event with your flag management system
  end
end

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

Develop a hook​

To develop a hook, 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. Implement your own hook by including the OpenFeature::SDK::Hooks::Hook module. You only need to define the stages you care about — unimplemented stages are no-ops by default.

class MyLoggingHook
  include OpenFeature::SDK::Hooks::Hook

  def before(hook_context:, hints:)
    puts "Evaluating #{hook_context.flag_key}"
    nil # Return nil or an EvaluationContext to merge
  end

  def after(hook_context:, evaluation_details:, hints:)
    puts "Result: #{evaluation_details.value}"
  end

  # error and finally are optional — only define what you need
end

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