diff --git a/sig/cognito_idp.rbs b/sig/cognito_idp.rbs
new file mode 100644
index 0000000..99b5e26
--- /dev/null
+++ b/sig/cognito_idp.rbs
@@ -0,0 +1,3 @@
+module CognitoIdp
+  VERSION: String
+end
diff --git a/sig/cognito_idp/authorization_uri.rbs b/sig/cognito_idp/authorization_uri.rbs
new file mode 100644
index 0000000..8a2b6c4
--- /dev/null
+++ b/sig/cognito_idp/authorization_uri.rbs
@@ -0,0 +1,25 @@
+module CognitoIdp
+  class AuthorizationUri
+    attr_reader client_id: String
+    attr_reader code_challenge_method: String?
+    attr_reader code_challenge: String?
+    attr_reader domain: String
+    attr_reader idp_identifier: String?
+    attr_reader identity_provider: String?
+    attr_reader nonce: String?
+    attr_reader redirect_uri: String
+    attr_reader response_type: Symbol
+    attr_reader scope: String | Array[String] | nil
+    attr_reader state: String?
+
+    def initialize: (client_id: String, domain: String, redirect_uri: String, ?response_type: Symbol, **untyped) -> void
+
+    def to_s: () -> String
+
+    private
+
+    def params: () -> Hash[Symbol, untyped]
+
+    def scope_string: () -> String?
+  end
+end
diff --git a/sig/cognito_idp/client.rbs b/sig/cognito_idp/client.rbs
index 6742dfb..84df8dd 100644
--- a/sig/cognito_idp/client.rbs
+++ b/sig/cognito_idp/client.rbs
@@ -1,6 +1,32 @@
 module CognitoIdp
-  module Client
-    VERSION: String
-    # See the writing guide of rbs: https://github.com/ruby/rbs#guides
+  class Client
+    attr_reader adapter: Symbol
+    attr_reader client_id: String
+    attr_reader client_secret: String?
+    attr_reader domain: String
+
+    def initialize: (client_id: String, domain: String, ?client_secret: String?, ?adapter: Symbol, ?stubs: untyped) -> void
+
+    def inspect: () -> String
+
+    def authorization_uri: (redirect_uri: String, **untyped) -> String
+
+    def get_token: (grant_type: String | Symbol, **untyped) -> Token
+                 | (grant_type: String | Symbol, **untyped) { (Token) -> void } -> Token
+
+    def get_user_info: (Token | String) -> UserInfo
+                     | (Token | String) { (UserInfo) -> void } -> UserInfo
+
+    def revoke_token: (Token | String) -> void
+
+    def logout_uri: (**untyped) -> String
+
+    private
+
+    def connection: () -> untyped
+
+    def handle_error_response: (untyped) -> void
+
+    def basic_authorization_headers: () -> Hash[String, String]?
   end
 end
diff --git a/sig/cognito_idp/error.rbs b/sig/cognito_idp/error.rbs
new file mode 100644
index 0000000..3c2a4ad
--- /dev/null
+++ b/sig/cognito_idp/error.rbs
@@ -0,0 +1,13 @@
+module CognitoIdp
+  class Error < StandardError
+    attr_reader error: String
+    attr_reader error_description: String?
+    attr_reader http_status: Integer?
+
+    def initialize: (error: String, ?error_description: String?, ?http_status: Integer?) -> void
+
+    private
+
+    def build_message: () -> String
+  end
+end
diff --git a/sig/cognito_idp/logout_uri.rbs b/sig/cognito_idp/logout_uri.rbs
new file mode 100644
index 0000000..157f9a7
--- /dev/null
+++ b/sig/cognito_idp/logout_uri.rbs
@@ -0,0 +1,21 @@
+module CognitoIdp
+  class LogoutUri
+    attr_reader client_id: String
+    attr_reader domain: String
+    attr_reader logout_uri: String?
+    attr_reader redirect_uri: String?
+    attr_reader response_type: Symbol?
+    attr_reader scope: String | Array[String] | nil
+    attr_reader state: String?
+
+    def initialize: (client_id: String, domain: String, **untyped) -> void
+
+    def to_s: () -> String
+
+    private
+
+    def params: () -> Hash[Symbol, untyped]
+
+    def scope_string: () -> String?
+  end
+end
diff --git a/sig/cognito_idp/token.rbs b/sig/cognito_idp/token.rbs
new file mode 100644
index 0000000..606d8d9
--- /dev/null
+++ b/sig/cognito_idp/token.rbs
@@ -0,0 +1,16 @@
+module CognitoIdp
+  class Token
+    attr_reader access_token: String?
+    attr_reader id_token: String?
+    attr_reader token_type: String?
+    attr_reader expires_at: Time?
+    attr_reader expires_in: Integer?
+    attr_reader refresh_token: String?
+
+    def initialize: (Hash[String | Symbol, untyped]) -> void
+
+    def expired?: () -> bool
+
+    def inspect: () -> String
+  end
+end
diff --git a/sig/cognito_idp/user_info.rbs b/sig/cognito_idp/user_info.rbs
new file mode 100644
index 0000000..4c0e92c
--- /dev/null
+++ b/sig/cognito_idp/user_info.rbs
@@ -0,0 +1,11 @@
+module CognitoIdp
+  class UserInfo
+    def initialize: (Hash[String | Symbol, untyped]) -> void
+
+    private
+
+    def method_missing: (Symbol, *untyped) -> untyped
+
+    def respond_to_missing?: (Symbol, ?bool) -> bool
+  end
+end