diff --git a/Gemfile.lock b/Gemfile.lock
index ef4da6e..df5efd1 100644
--- a/Gemfile.lock
+++ b/Gemfile.lock
@@ -9,6 +9,7 @@ GEM
   specs:
     benchmark (0.4.0)
     diff-lcs (1.6.2)
+    openfeature-sdk (0.6.5)
     rake (13.3.0)
     rspec (3.13.1)
       rspec-core (~> 3.13.0)
@@ -30,6 +31,7 @@ PLATFORMS
 
 DEPENDENCIES
   featurevisor!
+  openfeature-sdk (~> 0.6.5)
   rake (~> 13.0)
   rspec (~> 3.12)
 
diff --git a/README.md b/README.md
index 0faed19..75237ac 100644
--- a/README.md
+++ b/README.md
@@ -43,6 +43,7 @@ This SDK is compatible with Featurevisor v3 projects and v2 datafiles.
   - [Registering modules](#registering-modules)
 - [Child instance](#child-instance)
 - [Close](#close)
+- [OpenFeature](#openfeature)
 - [CLI usage](#cli-usage)
   - [Test](#test)
   - [Test against local monorepo's example-1](#test-against-local-monorepos-example-1)
@@ -811,6 +812,49 @@ $ bundle exec featurevisor assess-distribution \
   --n=1000
 ```
 
+## OpenFeature
+
+Install the official OpenFeature SDK next to Featurevisor:
+
+```ruby
+gem "featurevisor"
+gem "openfeature-sdk", "~> 0.6.5"
+```
+
+```ruby
+require "featurevisor/openfeature_provider"
+
+provider = Featurevisor::OpenFeatureProvider.new(
+  datafile: datafile_content,
+)
+
+OpenFeature::SDK.configure do |config|
+  config.set_provider_and_wait(provider)
+end
+
+client = OpenFeature::SDK.build_client
+enabled = client.fetch_boolean_value(
+  flag_key: "checkout",
+  default_value: false,
+  evaluation_context: OpenFeature::SDK::EvaluationContext.new(targeting_key: "user-123"),
+)
+```
+
+Use `checkout` for a flag, `checkout:variation` for its variation, and `checkout:title` for its `title` variable. Boolean variables use the boolean resolver. Arrays, hashes, and JSON variables use the object resolver.
+
+OpenFeature's targeting key maps to `userId` by default. `targeting_key_field`, `key_separator`, and `variation_key` can customize the mapping.
+
+You can also reuse an existing Featurevisor instance:
+
+```ruby
+featurevisor = Featurevisor.create_featurevisor(datafile: datafile_content)
+provider = Featurevisor::OpenFeatureProvider.new(featurevisor: featurevisor)
+```
+
+The caller owns an instance passed this way. Provider shutdown does not close it. Call `featurevisor.close` when every consumer is finished with it. When the provider creates the instance from options, the provider owns and closes it. If both are supplied, `featurevisor` takes precedence over the options hash.
+
+See the [OpenFeature provider guide](https://featurevisor.com/docs/sdks/openfeature/) for resolution reasons, errors, metadata, tracking, lifecycle, and providers for other languages.
+
 <!-- FEATUREVISOR_DOCS_END -->
 
 ## Development
diff --git a/featurevisor.gemspec b/featurevisor.gemspec
index 7a42ea8..5a2ff14 100644
--- a/featurevisor.gemspec
+++ b/featurevisor.gemspec
@@ -18,4 +18,5 @@ Gem::Specification.new do |spec|
   spec.add_dependency "benchmark", ">= 0"
   spec.add_development_dependency "rspec", "~> 3.12"
   spec.add_development_dependency "rake", "~> 13.0"
+  spec.add_development_dependency "openfeature-sdk", "~> 0.6.5"
 end
diff --git a/lib/featurevisor/openfeature_provider.rb b/lib/featurevisor/openfeature_provider.rb
new file mode 100644
index 0000000..ab04195
--- /dev/null
+++ b/lib/featurevisor/openfeature_provider.rb
@@ -0,0 +1,187 @@
+# frozen_string_literal: true
+
+require "json"
+require "time"
+require "open_feature/sdk"
+require_relative "../featurevisor"
+
+module Featurevisor
+  class OpenFeatureProvider
+    Provider = OpenFeature::SDK::Provider
+
+    attr_reader :metadata, :featurevisor
+
+    def initialize(options = {}, featurevisor: nil, targeting_key_field: "userId", key_separator: ":", variation_key: "variation", on_track: nil)
+      @metadata = Provider::ProviderMetadata.new(name: "Featurevisor").freeze
+      @targeting_key_field = targeting_key_field.empty? ? "userId" : targeting_key_field
+      @key_separator = key_separator.empty? ? ":" : key_separator
+      @variation_key = variation_key.empty? ? "variation" : variation_key
+      @on_track = on_track
+      @datafile_error = nil
+      @owns_featurevisor = featurevisor.nil?
+      if featurevisor
+        @featurevisor = featurevisor
+      else
+        resolved_options = options.dup
+        original_handler = resolved_options[:onDiagnostic] || resolved_options[:on_diagnostic]
+        resolved_options[:onDiagnostic] = lambda do |diagnostic|
+          @datafile_error = diagnostic[:message] if diagnostic[:code] == "invalid_datafile"
+          @datafile_error = nil if diagnostic[:code] == "datafile_set"
+          original_handler&.call(diagnostic)
+        end
+        @featurevisor = Featurevisor.create_featurevisor(resolved_options)
+      end
+      @datafile_unsubscribe = @featurevisor.on("datafile_set", ->(*) { @datafile_error = nil })
+    end
+
+    def init(_evaluation_context = nil); end
+    def shutdown
+      @datafile_unsubscribe&.call
+      featurevisor.close if @owns_featurevisor
+    end
+    def hooks = []
+
+    def track(tracking_event_name:, evaluation_context: nil, tracking_event_details: nil)
+      @on_track&.call(tracking_event_name, evaluation_context, tracking_event_details)
+    end
+
+    def fetch_boolean_value(flag_key:, default_value:, evaluation_context: nil)
+      resolve(flag_key, default_value, evaluation_context, :boolean)
+    end
+
+    def fetch_string_value(flag_key:, default_value:, evaluation_context: nil)
+      resolve(flag_key, default_value, evaluation_context, :string)
+    end
+
+    def fetch_number_value(flag_key:, default_value:, evaluation_context: nil)
+      resolve(flag_key, default_value, evaluation_context, :number)
+    end
+
+    alias fetch_integer_value fetch_number_value
+    alias fetch_float_value fetch_number_value
+
+    def fetch_object_value(flag_key:, default_value:, evaluation_context: nil)
+      resolve(flag_key, default_value, evaluation_context, :object)
+    end
+
+    private
+
+    def resolve(flag_key, default_value, evaluation_context, expected_type)
+      return error(default_value, Provider::ErrorCode::PARSE_ERROR, @datafile_error) if @datafile_error
+
+      feature_key, selector = split_key(flag_key)
+      context = normalize(evaluation_context&.fields || {})
+      targeting_key = evaluation_context&.targeting_key
+      context[@targeting_key_field] = targeting_key if targeting_key && !targeting_key.empty?
+
+      if selector.nil? || selector.empty?
+        return type_mismatch(flag_key, default_value, expected_type) unless expected_type == :boolean
+        evaluation = featurevisor.evaluate_flag(feature_key, context)
+        value = evaluation[:enabled]
+      elsif selector == @variation_key
+        evaluation = featurevisor.evaluate_variation(feature_key, context)
+        value = evaluation[:variation_value] || evaluation.dig(:variation, :value)
+      else
+        evaluation = featurevisor.evaluate_variable(feature_key, selector, context)
+        value = evaluation[:variable_value]
+        if evaluation.dig(:variable_schema, :type) == "json" && value.is_a?(String)
+          begin
+            value = JSON.parse(value)
+          rescue JSON::ParserError
+            # Type validation below returns TYPE_MISMATCH when object was requested.
+          end
+        end
+      end
+
+      metadata = metadata_for(evaluation)
+      code = error_code(evaluation[:reason])
+      return error(default_value, code, error_message(evaluation), metadata) if code
+      value = default_value if value.nil?
+      value = normalize(value) if expected_type == :object
+      return type_mismatch(flag_key, default_value, expected_type, metadata) unless matches?(value, expected_type)
+
+      Provider::ResolutionDetails.new(
+        value: value,
+        reason: reason(evaluation[:reason]),
+        variant: variant(evaluation),
+        flag_metadata: metadata
+      )
+    end
+
+    def split_key(key)
+      index = key.index(@key_separator)
+      index ? [key[0...index], key[(index + @key_separator.length)..]] : [key, nil]
+    end
+
+    def metadata_for(evaluation)
+      metadata = {
+        "featureKey" => evaluation[:feature_key],
+        "featurevisorReason" => evaluation[:reason],
+        "schemaVersion" => featurevisor.get_schema_version
+      }
+      metadata["revision"] = featurevisor.get_revision if featurevisor.get_revision
+      {
+        variable_key: "variableKey",
+        rule_key: "ruleKey",
+        bucket_key: "bucketKey",
+        bucket_value: "bucketValue",
+        force_index: "forceIndex",
+        variable_override_index: "variableOverrideIndex"
+      }.each do |key, metadata_key|
+        metadata[metadata_key] = evaluation[key] unless evaluation[key].nil?
+      end
+      metadata
+    end
+
+    def reason(value)
+      return Provider::Reason::ERROR if %w[feature_not_found variable_not_found no_variations error].include?(value)
+      return Provider::Reason::TARGETING_MATCH if %w[required forced sticky rule variable_override_variation variable_override_rule].include?(value)
+      return Provider::Reason::SPLIT if value == "allocated"
+      return Provider::Reason::DISABLED if %w[disabled variation_disabled variable_disabled].include?(value)
+      Provider::Reason::DEFAULT
+    end
+
+    def error_code(value)
+      return Provider::ErrorCode::FLAG_NOT_FOUND if %w[feature_not_found variable_not_found no_variations].include?(value)
+      return Provider::ErrorCode::GENERAL if value == "error"
+      nil
+    end
+
+    def error_message(evaluation)
+      return evaluation[:error].message if evaluation[:error].respond_to?(:message)
+      return %(Feature "#{evaluation[:feature_key]}" was not found) if evaluation[:reason] == "feature_not_found"
+      return %(Variable "#{evaluation[:variable_key]}" was not found for feature "#{evaluation[:feature_key]}") if evaluation[:reason] == "variable_not_found"
+      return %(Feature "#{evaluation[:feature_key]}" has no variations) if evaluation[:reason] == "no_variations"
+      "Featurevisor evaluation failed"
+    end
+
+    def variant(evaluation) = evaluation[:variation_value] || evaluation.dig(:variation, :value)
+
+    def matches?(value, type)
+      case type
+      when :boolean then value == true || value == false
+      when :string then value.is_a?(String)
+      when :number then value.is_a?(Numeric) && value.finite?
+      when :object then value.is_a?(Hash) || value.is_a?(Array)
+      else false
+      end
+    end
+
+    def normalize(value)
+      case value
+      when Time, DateTime then value.iso8601
+      when Hash then value.to_h { |key, item| [key.to_s, normalize(item)] }
+      when Array then value.map { |item| normalize(item) }
+      else value
+      end
+    end
+
+    def error(value, code, message, metadata = {})
+      Provider::ResolutionDetails.new(value: value, reason: Provider::Reason::ERROR, error_code: code, error_message: message, flag_metadata: metadata)
+    end
+
+    def type_mismatch(key, value, expected_type, metadata = {})
+      error(value, Provider::ErrorCode::TYPE_MISMATCH, %(Flag "#{key}" did not resolve to a #{expected_type} value), metadata)
+    end
+  end
+end
diff --git a/spec/openfeature_provider_spec.rb b/spec/openfeature_provider_spec.rb
new file mode 100644
index 0000000..baad944
--- /dev/null
+++ b/spec/openfeature_provider_spec.rb
@@ -0,0 +1,89 @@
+require "featurevisor/openfeature_provider"
+
+RSpec.describe Featurevisor::OpenFeatureProvider do
+  let(:datafile) do
+    {
+      schemaVersion: "2", revision: "openfeature-test", segments: {},
+      features: {
+        "checkout" => {
+          bucketBy: "userId",
+          variations: [{ value: "on", variables: { title: "Hello", count: 3, ratio: 1.5, visible: true, items: ["a"], config: { color: "blue" }, json: '{"nested":true}' } }],
+          variablesSchema: {
+            title: { type: "string", defaultValue: "Default" }, count: { type: "integer", defaultValue: 0 },
+            ratio: { type: "double", defaultValue: 0 }, visible: { type: "boolean", defaultValue: false },
+            items: { type: "array", defaultValue: [] }, config: { type: "object", defaultValue: {} }, json: { type: "json", defaultValue: "{}" }
+          },
+          force: [{ conditions: { attribute: "userId", operator: "equals", value: "forced-user" }, enabled: true, variation: "on" }],
+          traffic: [{ key: "all", segments: "*", percentage: 100_000, variation: "on" }]
+        }
+      }
+    }
+  end
+
+  def provider(**options)
+    described_class.new({ datafile: datafile, logLevel: "fatal" }, **options)
+  end
+
+  it "resolves every OpenFeature type and maps targeting key" do
+    context = OpenFeature::SDK::EvaluationContext.new(targeting_key: "forced-user")
+    expect(provider.fetch_boolean_value(flag_key: "checkout", default_value: false, evaluation_context: context).value).to be(true)
+    expect(provider.fetch_string_value(flag_key: "checkout:variation", default_value: "fallback", evaluation_context: context).value).to eq("on")
+    expect(provider.fetch_string_value(flag_key: "checkout:title", default_value: "fallback", evaluation_context: context).value).to eq("Hello")
+    expect(provider.fetch_integer_value(flag_key: "checkout:count", default_value: 0, evaluation_context: context).value).to eq(3)
+    expect(provider.fetch_float_value(flag_key: "checkout:ratio", default_value: 0.0, evaluation_context: context).value).to eq(1.5)
+    expect(provider.fetch_boolean_value(flag_key: "checkout:visible", default_value: false, evaluation_context: context).value).to be(true)
+    expect(provider.fetch_object_value(flag_key: "checkout:items", default_value: [], evaluation_context: context).value).to eq(["a"])
+    expect(provider.fetch_object_value(flag_key: "checkout:config", default_value: {}, evaluation_context: context).value).to eq({ "color" => "blue" })
+    expect(provider.fetch_object_value(flag_key: "checkout:json", default_value: {}, evaluation_context: context).value).to eq({ "nested" => true })
+  end
+
+  it "supports errors, custom grammar, tracking, and shutdown" do
+    tracked = []
+    instance = provider(key_separator: "/", variation_key: "$variation", on_track: ->(*args) { tracked << args })
+    expect(instance.fetch_string_value(flag_key: "checkout/$variation", default_value: "fallback").value).to eq("on")
+    expect(instance.fetch_string_value(flag_key: "missing", default_value: "fallback").error_code).to eq(OpenFeature::SDK::Provider::ErrorCode::TYPE_MISMATCH)
+    missing = instance.fetch_boolean_value(flag_key: "missing", default_value: true)
+    expect(missing.value).to be(true)
+    expect(missing.error_code).to eq(OpenFeature::SDK::Provider::ErrorCode::FLAG_NOT_FOUND)
+    instance.track(tracking_event_name: "purchase")
+    expect(tracked.first.first).to eq("purchase")
+    instance.shutdown
+  end
+
+  it "works through the OpenFeature SDK" do
+    OpenFeature::SDK.configure { |configuration| configuration.set_provider_and_wait(provider) }
+    client = OpenFeature::SDK.build_client
+    value = client.fetch_boolean_value(
+      flag_key: "checkout",
+      default_value: false,
+      evaluation_context: OpenFeature::SDK::EvaluationContext.new(targeting_key: "forced-user")
+    )
+    expect(value).to be(true)
+  end
+
+  it "returns a parse error for malformed datafiles" do
+    instance = described_class.new({ datafile: "{", logLevel: "fatal" })
+    result = instance.fetch_boolean_value(flag_key: "checkout", default_value: false)
+    expect(result.error_code).to eq(OpenFeature::SDK::Provider::ErrorCode::PARSE_ERROR)
+    expect(result.error_message).to eq("Could not parse datafile")
+    instance.featurevisor.set_datafile(datafile, true)
+    expect(instance.fetch_boolean_value(flag_key: "checkout", default_value: false).value).to be(true)
+  end
+
+  it "borrows an existing Featurevisor instance" do
+    closed = false
+    featurevisor = Featurevisor.create_featurevisor(
+      datafile: datafile,
+      logLevel: "fatal",
+      modules: [{ name: "owner", close: -> { closed = true } }]
+    )
+    instance = described_class.new(featurevisor: featurevisor)
+
+    expect(instance.featurevisor).to equal(featurevisor)
+    instance.shutdown
+    expect(closed).to be(false)
+
+    featurevisor.close
+    expect(closed).to be(true)
+  end
+end