diff --git a/.github/workflows/main.yml b/.github/workflows/main.yml
index 4ca916ee..3130561f 100644
--- a/.github/workflows/main.yml
+++ b/.github/workflows/main.yml
@@ -43,6 +43,17 @@ jobs:
       - run: bundle install
       - name: Rubocop
         run: bundle exec rubocop --color
+  steep:
+    runs-on: ubuntu-latest
+    name: Steep
+    steps:
+      - uses: actions/checkout@v3
+      - uses: ruby/setup-ruby@v1
+        with:
+          ruby-version: 3.2
+      - run: bundle install
+      - name: Steep
+        run: bundle exec steep check
   # check the status of other jobs, so we can have a single job dependency for branch protection
   # https://github.com/community/community/discussions/4324#discussioncomment-3477871
   status:
diff --git a/Gemfile.lock b/Gemfile.lock
index 5817217a..69a1bd5f 100644
--- a/Gemfile.lock
+++ b/Gemfile.lock
@@ -6,16 +6,38 @@ PATH
 GEM
   remote: https://rubygems.org/
   specs:
+    activesupport (7.0.8)
+      concurrent-ruby (~> 1.0, >= 1.0.2)
+      i18n (>= 1.6, < 2)
+      minitest (>= 5.1)
+      tzinfo (~> 2.0)
     ast (2.4.2)
     concurrent-ruby (1.2.2)
+    csv (3.2.7)
     diff-lcs (1.5.0)
+    ffi (1.15.5)
+    ffi (1.15.5-x64-mingw-ucrt)
+    ffi (1.15.5-x64-mingw32)
+    fileutils (1.7.1)
+    i18n (1.14.1)
+      concurrent-ruby (~> 1.0)
     json (2.6.2)
+    language_server-protocol (3.17.0.3)
+    listen (3.8.0)
+      rb-fsevent (~> 0.10, >= 0.10.3)
+      rb-inotify (~> 0.9, >= 0.9.10)
+    logger (1.5.3)
     markly (0.7.0)
+    minitest (5.20.0)
     parallel (1.22.1)
     parser (3.1.2.1)
       ast (~> 2.4.1)
     rainbow (3.1.1)
     rake (13.0.6)
+    rb-fsevent (0.11.2)
+    rb-inotify (0.10.1)
+      ffi (~> 1.0)
+    rbs (3.2.1)
     regexp_parser (2.6.0)
     rexml (3.2.5)
     rspec (3.12.0)
@@ -44,6 +66,27 @@ GEM
     rubocop-ast (1.23.0)
       parser (>= 3.1.1.0)
     ruby-progressbar (1.11.0)
+    securerandom (0.2.2)
+    steep (1.5.3)
+      activesupport (>= 5.1)
+      concurrent-ruby (>= 1.1.10)
+      csv (>= 3.0.9)
+      fileutils (>= 1.1.0)
+      json (>= 2.1.0)
+      language_server-protocol (>= 3.15, < 4.0)
+      listen (~> 3.0)
+      logger (>= 1.3.0)
+      parser (>= 3.1)
+      rainbow (>= 2.2.2, < 4.0)
+      rbs (>= 3.1.0)
+      securerandom (>= 0.1)
+      strscan (>= 1.0.0)
+      terminal-table (>= 2, < 4)
+    strscan (3.0.6)
+    terminal-table (3.0.2)
+      unicode-display_width (>= 1.1.1, < 3)
+    tzinfo (2.0.6)
+      concurrent-ruby (~> 1.0)
     unicode-display_width (2.3.0)
 
 PLATFORMS
@@ -63,6 +106,7 @@ DEPENDENCIES
   rake (~> 13.0)
   rspec (~> 3.12.0)
   rubocop (~> 1.37.1)
+  steep (~> 1.5.0)
 
 BUNDLED WITH
    2.3.25
diff --git a/Steepfile b/Steepfile
new file mode 100644
index 00000000..4c720955
--- /dev/null
+++ b/Steepfile
@@ -0,0 +1,10 @@
+# frozen_string_literal: true
+
+target :lib do
+  signature "sig"
+  check "lib"
+  library "pathname"
+  library "forwardable"
+  library "singleton"
+  library "uri"
+end
diff --git a/lib/openfeature/sdk/metadata.rb b/lib/openfeature/sdk/metadata.rb
index 411ae1d5..e9bf2423 100644
--- a/lib/openfeature/sdk/metadata.rb
+++ b/lib/openfeature/sdk/metadata.rb
@@ -26,7 +26,7 @@ def initialize(name:, version: nil)
       end
 
       def ==(other)
-        raise ArgumentError("Expected comparison to be between Metadata object") unless other.is_a?(Metadata)
+        raise ArgumentError, "Expected comparison to be between Metadata object" unless other.is_a?(Metadata)
 
         @name == other.name && @version == other.version
       end
diff --git a/openfeature-sdk.gemspec b/openfeature-sdk.gemspec
index f507b227..3f38eecf 100644
--- a/openfeature-sdk.gemspec
+++ b/openfeature-sdk.gemspec
@@ -35,4 +35,5 @@ Gem::Specification.new do |spec|
   spec.add_development_dependency "rake", "~> 13.0"
   spec.add_development_dependency "rspec", "~> 3.12.0"
   spec.add_development_dependency "rubocop", "~> 1.37.1"
+  spec.add_development_dependency "steep", "~> 1.5.0"
 end
diff --git a/sig/openfeature/sdk.rbs b/sig/openfeature/sdk.rbs
index e058802f..863cd7ba 100644
--- a/sig/openfeature/sdk.rbs
+++ b/sig/openfeature/sdk.rbs
@@ -1,5 +1,5 @@
-module Openfeature
-  module Sdk
+module OpenFeature
+  module SDK
     VERSION: String
     # See the writing guide of rbs: https://github.com/ruby/rbs#guides
   end
diff --git a/sig/openfeature/sdk/_hook.rbs b/sig/openfeature/sdk/_hook.rbs
new file mode 100644
index 00000000..f82584c8
--- /dev/null
+++ b/sig/openfeature/sdk/_hook.rbs
@@ -0,0 +1,31 @@
+type flagValue = bool | Numeric | String | Hash[String, untyped]
+type flagValueType = :bool | :integer | :float | :string | :object
+type evaluationContext = { targeting_key: String? }
+type evaluationDetails = { flag_key: String, flag_value?: flagValue }
+
+type hookContext[T] = {
+    flag_key: String,
+    flag_value_type: flagValueType,
+    evaluation_context: evaluationContext,
+    default_value: T,
+  }
+
+type hookHints = Hash[String, flagValue]
+
+interface _BeforeHook
+  def before: (evaluationContext, ?hookHints) -> (evaluationContext | void)
+end
+
+interface _AfterHook[T]
+  def after: (hookContext[T], evaluationDetails, ?hookHints) -> void
+end
+
+interface _ErrorHook[T]
+  def error: (hookContext[T], Exception, ?hookHints) -> void
+end
+
+interface _FinallyHook[T]
+  def finally: (hookContext[T], ?hookHints) -> void
+end
+
+type hook = _BeforeHook | _AfterHook[flagValue] | _ErrorHook[flagValue] | _FinallyHook[flagValue]
diff --git a/sig/openfeature/sdk/api.rbs b/sig/openfeature/sdk/api.rbs
new file mode 100644
index 00000000..61bf5037
--- /dev/null
+++ b/sig/openfeature/sdk/api.rbs
@@ -0,0 +1,22 @@
+module OpenFeature
+  module SDK
+
+    interface _Configuration
+      def context: () -> void
+    end
+
+    class API
+      include _Configuration
+      extend Forwardable
+
+      attr_reader configuration: Configuration
+
+      def build_client: -> Client
+
+      def configure: () { (Configuration) -> void } -> void
+
+      # Singleton's RBS doesn't quite work
+      def self.instance: () -> instance
+    end
+  end
+end
diff --git a/sig/openfeature/sdk/client.rbs b/sig/openfeature/sdk/client.rbs
new file mode 100644
index 00000000..f44c9983
--- /dev/null
+++ b/sig/openfeature/sdk/client.rbs
@@ -0,0 +1,17 @@
+module OpenFeature
+  module SDK
+    class Client
+      RESULT_TYPE: Array[Symbol]
+      SUFFIXES: Array[Symbol]
+
+      @context: evaluationContext
+      @hooks: Array[hook]
+
+      attr_accessor hooks: Array[hook]
+      attr_reader metadata: Metadata?
+      attr_reader provider: untyped
+
+      def initialize: (provider: untyped , client_options: untyped, context: untyped) -> void
+    end
+  end
+end
diff --git a/sig/openfeature/sdk/configuration.rbs b/sig/openfeature/sdk/configuration.rbs
new file mode 100644
index 00000000..dc5578c1
--- /dev/null
+++ b/sig/openfeature/sdk/configuration.rbs
@@ -0,0 +1,19 @@
+
+module Concurrent
+  class Array[T] < ::Array[T]
+    def initialize: (?::Array[T]) -> void
+  end
+end
+
+module OpenFeature
+  module SDK
+    class Configuration
+      extend Forwardable
+
+      attr_accessor context: evaluationContext
+      attr_accessor hooks: [hook]
+      attr_accessor metadata: Metadata
+      attr_accessor provider: untyped
+    end
+  end
+end
diff --git a/sig/openfeature/sdk/metadata.rbs b/sig/openfeature/sdk/metadata.rbs
new file mode 100644
index 00000000..afe46df6
--- /dev/null
+++ b/sig/openfeature/sdk/metadata.rbs
@@ -0,0 +1,12 @@
+module OpenFeature
+  module SDK
+    class Metadata
+      attr_reader name: String
+      attr_reader version: String?
+
+      def initialize: (name: String, ?version: String?) -> void
+
+      def ==: (untyped other) -> untyped
+    end
+  end
+end
diff --git a/sig/openfeature/sdk/provider/no_op_provider.rbs b/sig/openfeature/sdk/provider/no_op_provider.rbs
new file mode 100644
index 00000000..91f8fd21
--- /dev/null
+++ b/sig/openfeature/sdk/provider/no_op_provider.rbs
@@ -0,0 +1,30 @@
+module OpenFeature
+  module SDK
+    module Provider
+      class NoOpProvider
+        REASON_NO_OP: String
+        NAME: String
+        class ResolutionDetails[T] < ::Struct[T]
+          def initialize : (value: T, reason: String) -> void
+
+          attr_reader value(): T
+          attr_reader reason(): untyped
+          attr_reader variant(): untyped
+          attr_reader error_code(): untyped
+          attr_reader error_message(): untyped
+        end
+
+        attr_reader metadata: Metadata
+
+        def fetch_boolean_value: (flag_key: String, default_value: bool, ?evaluation_context: evaluationContext?) -> ResolutionDetails[bool]
+
+        def fetch_string_value: (flag_key: String, default_value: String, ?evaluation_context: evaluationContext?) -> ResolutionDetails[String]
+
+        def fetch_number_value: (flag_key: String, default_value: Numeric, ?evaluation_context: evaluationContext?) -> ResolutionDetails[Numeric]
+
+        def fetch_object_value: (flag_key: String, default_value: Hash[String|Symbol, untyped], ?evaluation_context: evaluationContext?) -> ResolutionDetails[Hash[String|Symbol, untyped]]
+        def no_op: [X] (X) -> ResolutionDetails[X]
+      end
+    end
+  end
+end