diff --git a/README.md b/README.md
index c97362d..920471c 100644
--- a/README.md
+++ b/README.md
@@ -329,6 +329,13 @@ class TestToolWithStructuredContentResponse < ModelContextProtocol::Server::Tool
         required: ["temperature", "conditions", "humidity"]
       }
     end
+    # Optional security requirements for the tool
+    security_schemes do
+      [
+        {type: "noauth"},
+        {type: "oauth2", scopes: ["search.read"]}
+      ]
+    end
   end
 
   def call
@@ -362,6 +369,7 @@ end
 
 Key features:
 - Define input and output JSON schemas
+- Declare tool security schemes (e.g., noauth, oauth2 scopes)
 - Return text, image, audio, or embedded resource content
 - Support for structured content responses
 - Cancellable and progressable operations
diff --git a/lib/model_context_protocol/server/tool.rb b/lib/model_context_protocol/server/tool.rb
index 383e6b2..31b16fc 100644
--- a/lib/model_context_protocol/server/tool.rb
+++ b/lib/model_context_protocol/server/tool.rb
@@ -83,7 +83,7 @@ def serialized
     end
 
     class << self
-      attr_reader :name, :description, :title, :input_schema, :output_schema, :annotations
+      attr_reader :name, :description, :title, :input_schema, :output_schema, :annotations, :security_schemes
 
       def define(&block)
         definition_dsl = DefinitionDSL.new
@@ -95,6 +95,7 @@ def define(&block)
         @input_schema = definition_dsl.input_schema
         @output_schema = definition_dsl.output_schema
         @annotations = definition_dsl.annotations
+        @security_schemes = definition_dsl.security_schemes
       end
 
       def inherited(subclass)
@@ -104,6 +105,7 @@ def inherited(subclass)
         subclass.instance_variable_set(:@input_schema, @input_schema)
         subclass.instance_variable_set(:@output_schema, @output_schema)
         subclass.instance_variable_set(:@annotations, @annotations)
+        subclass.instance_variable_set(:@security_schemes, @security_schemes)
       end
 
       def call(arguments, client_logger, server_logger, context = {})
@@ -123,6 +125,7 @@ def definition
         result[:title] = @title if @title
         result[:outputSchema] = @output_schema if @output_schema
         result[:annotations] = @annotations if @annotations
+        result[:securitySchemes] = @security_schemes if @security_schemes
         result
       end
     end
@@ -157,6 +160,11 @@ def annotations(&block)
         @annotations = instance_eval(&block) if block_given?
         @annotations
       end
+
+      def security_schemes(&block)
+        @security_schemes = instance_eval(&block) if block_given?
+        @security_schemes
+      end
     end
   end
 end
diff --git a/spec/lib/model_context_protocol/server/tool_spec.rb b/spec/lib/model_context_protocol/server/tool_spec.rb
index f7f8898..0405188 100644
--- a/spec/lib/model_context_protocol/server/tool_spec.rb
+++ b/spec/lib/model_context_protocol/server/tool_spec.rb
@@ -335,6 +335,53 @@
       child_tool = Class.new(parent_tool)
       expect(child_tool.annotations).to eq({readOnlyHint: true})
     end
+
+    it "sets security schemes when provided" do
+      tool_with_security_schemes = Class.new(ModelContextProtocol::Server::Tool) do
+        define do
+          name "search"
+          description "Search indexed documents"
+          input_schema { {type: "object", properties: {}, required: []} }
+          security_schemes do
+            [
+              {type: "noauth"},
+              {type: "oauth2", scopes: ["search.read"]}
+            ]
+          end
+        end
+      end
+
+      expect(tool_with_security_schemes.security_schemes).to eq(
+        [
+          {type: "noauth"},
+          {type: "oauth2", scopes: ["search.read"]}
+        ]
+      )
+    end
+
+    it "inherits security schemes in subclasses" do
+      parent_tool = Class.new(ModelContextProtocol::Server::Tool) do
+        define do
+          name "search"
+          description "Search indexed documents"
+          input_schema { {type: "object", properties: {}, required: []} }
+          security_schemes do
+            [
+              {type: "noauth"},
+              {type: "oauth2", scopes: ["search.read"]}
+            ]
+          end
+        end
+      end
+
+      child_tool = Class.new(parent_tool)
+      expect(child_tool.security_schemes).to eq(
+        [
+          {type: "noauth"},
+          {type: "oauth2", scopes: ["search.read"]}
+        ]
+      )
+    end
   end
 
   describe "definition" do
@@ -430,6 +477,52 @@
         annotations: {readOnlyHint: true}
       )
     end
+
+    it "includes security schemes when provided" do
+      tool_with_security_schemes = Class.new(ModelContextProtocol::Server::Tool) do
+        define do
+          name "search"
+          description "Search indexed documents"
+          input_schema do
+            {
+              type: "object",
+              properties: {
+                q: {
+                  type: "string",
+                  description: "Search query"
+                }
+              },
+              required: ["q"]
+            }
+          end
+          security_schemes do
+            [
+              {type: "noauth"},
+              {type: "oauth2", scopes: ["search.read"]}
+            ]
+          end
+        end
+      end
+
+      expect(tool_with_security_schemes.definition).to eq(
+        name: "search",
+        description: "Search indexed documents",
+        inputSchema: {
+          type: "object",
+          properties: {
+            q: {
+              type: "string",
+              description: "Search query"
+            }
+          },
+          required: ["q"]
+        },
+        securitySchemes: [
+          {type: "noauth"},
+          {type: "oauth2", scopes: ["search.read"]}
+        ]
+      )
+    end
   end
 
   describe "optional title field" do
@@ -458,6 +551,11 @@ def call
       metadata = tool_without_title.definition
       expect(metadata).not_to have_key(:annotations)
     end
+
+    it "does not include security schemes in definition when not provided" do
+      metadata = tool_without_title.definition
+      expect(metadata).not_to have_key(:securitySchemes)
+    end
   end
 
   describe "server logger integration" do