diff --git a/api/kotlin-sdk.api b/api/kotlin-sdk.api
index 4f0b20c..8235882 100644
--- a/api/kotlin-sdk.api
+++ b/api/kotlin-sdk.api
@@ -1,3 +1,34 @@
+public final class io/modelcontextprotocol/kotlin/sdk/AudioContent : io/modelcontextprotocol/kotlin/sdk/PromptMessageContentMultimodal {
+	public static final field Companion Lio/modelcontextprotocol/kotlin/sdk/AudioContent$Companion;
+	public static final field TYPE Ljava/lang/String;
+	public fun <init> (Ljava/lang/String;Ljava/lang/String;)V
+	public final fun component1 ()Ljava/lang/String;
+	public final fun component2 ()Ljava/lang/String;
+	public final fun copy (Ljava/lang/String;Ljava/lang/String;)Lio/modelcontextprotocol/kotlin/sdk/AudioContent;
+	public static synthetic fun copy$default (Lio/modelcontextprotocol/kotlin/sdk/AudioContent;Ljava/lang/String;Ljava/lang/String;ILjava/lang/Object;)Lio/modelcontextprotocol/kotlin/sdk/AudioContent;
+	public fun equals (Ljava/lang/Object;)Z
+	public final fun getData ()Ljava/lang/String;
+	public final fun getMimeType ()Ljava/lang/String;
+	public fun getType ()Ljava/lang/String;
+	public fun hashCode ()I
+	public fun toString ()Ljava/lang/String;
+}
+
+public synthetic class io/modelcontextprotocol/kotlin/sdk/AudioContent$$serializer : kotlinx/serialization/internal/GeneratedSerializer {
+	public static final field INSTANCE Lio/modelcontextprotocol/kotlin/sdk/AudioContent$$serializer;
+	public final fun childSerializers ()[Lkotlinx/serialization/KSerializer;
+	public final fun deserialize (Lkotlinx/serialization/encoding/Decoder;)Lio/modelcontextprotocol/kotlin/sdk/AudioContent;
+	public synthetic fun deserialize (Lkotlinx/serialization/encoding/Decoder;)Ljava/lang/Object;
+	public final fun getDescriptor ()Lkotlinx/serialization/descriptors/SerialDescriptor;
+	public final fun serialize (Lkotlinx/serialization/encoding/Encoder;Lio/modelcontextprotocol/kotlin/sdk/AudioContent;)V
+	public synthetic fun serialize (Lkotlinx/serialization/encoding/Encoder;Ljava/lang/Object;)V
+	public fun typeParametersSerializers ()[Lkotlinx/serialization/KSerializer;
+}
+
+public final class io/modelcontextprotocol/kotlin/sdk/AudioContent$Companion {
+	public final fun serializer ()Lkotlinx/serialization/KSerializer;
+}
+
 public final class io/modelcontextprotocol/kotlin/sdk/BlobResourceContents : io/modelcontextprotocol/kotlin/sdk/ResourceContents {
 	public static final field Companion Lio/modelcontextprotocol/kotlin/sdk/BlobResourceContents$Companion;
 	public fun <init> (Ljava/lang/String;Ljava/lang/String;Ljava/lang/String;)V
@@ -1665,6 +1696,14 @@ public final class io/modelcontextprotocol/kotlin/sdk/PromptMessageContent$Compa
 	public final fun serializer ()Lkotlinx/serialization/KSerializer;
 }
 
+public abstract interface class io/modelcontextprotocol/kotlin/sdk/PromptMessageContentMultimodal : io/modelcontextprotocol/kotlin/sdk/PromptMessageContent {
+	public static final field Companion Lio/modelcontextprotocol/kotlin/sdk/PromptMessageContentMultimodal$Companion;
+}
+
+public final class io/modelcontextprotocol/kotlin/sdk/PromptMessageContentMultimodal$Companion {
+	public final fun serializer ()Lkotlinx/serialization/KSerializer;
+}
+
 public abstract interface class io/modelcontextprotocol/kotlin/sdk/PromptMessageContentTextOrImage : io/modelcontextprotocol/kotlin/sdk/PromptMessageContent {
 	public static final field Companion Lio/modelcontextprotocol/kotlin/sdk/PromptMessageContentTextOrImage$Companion;
 }
@@ -2404,13 +2443,15 @@ public final class io/modelcontextprotocol/kotlin/sdk/TextResourceContents$Compa
 
 public final class io/modelcontextprotocol/kotlin/sdk/Tool {
 	public static final field Companion Lio/modelcontextprotocol/kotlin/sdk/Tool$Companion;
-	public fun <init> (Ljava/lang/String;Ljava/lang/String;Lio/modelcontextprotocol/kotlin/sdk/Tool$Input;)V
+	public fun <init> (Ljava/lang/String;Ljava/lang/String;Lio/modelcontextprotocol/kotlin/sdk/Tool$Input;Lio/modelcontextprotocol/kotlin/sdk/ToolAnnotations;)V
 	public final fun component1 ()Ljava/lang/String;
 	public final fun component2 ()Ljava/lang/String;
 	public final fun component3 ()Lio/modelcontextprotocol/kotlin/sdk/Tool$Input;
-	public final fun copy (Ljava/lang/String;Ljava/lang/String;Lio/modelcontextprotocol/kotlin/sdk/Tool$Input;)Lio/modelcontextprotocol/kotlin/sdk/Tool;
-	public static synthetic fun copy$default (Lio/modelcontextprotocol/kotlin/sdk/Tool;Ljava/lang/String;Ljava/lang/String;Lio/modelcontextprotocol/kotlin/sdk/Tool$Input;ILjava/lang/Object;)Lio/modelcontextprotocol/kotlin/sdk/Tool;
+	public final fun component4 ()Lio/modelcontextprotocol/kotlin/sdk/ToolAnnotations;
+	public final fun copy (Ljava/lang/String;Ljava/lang/String;Lio/modelcontextprotocol/kotlin/sdk/Tool$Input;Lio/modelcontextprotocol/kotlin/sdk/ToolAnnotations;)Lio/modelcontextprotocol/kotlin/sdk/Tool;
+	public static synthetic fun copy$default (Lio/modelcontextprotocol/kotlin/sdk/Tool;Ljava/lang/String;Ljava/lang/String;Lio/modelcontextprotocol/kotlin/sdk/Tool$Input;Lio/modelcontextprotocol/kotlin/sdk/ToolAnnotations;ILjava/lang/Object;)Lio/modelcontextprotocol/kotlin/sdk/Tool;
 	public fun equals (Ljava/lang/Object;)Z
+	public final fun getAnnotations ()Lio/modelcontextprotocol/kotlin/sdk/ToolAnnotations;
 	public final fun getDescription ()Ljava/lang/String;
 	public final fun getInputSchema ()Lio/modelcontextprotocol/kotlin/sdk/Tool$Input;
 	public final fun getName ()Ljava/lang/String;
@@ -2465,6 +2506,42 @@ public final class io/modelcontextprotocol/kotlin/sdk/Tool$Input$Companion {
 	public final fun serializer ()Lkotlinx/serialization/KSerializer;
 }
 
+public final class io/modelcontextprotocol/kotlin/sdk/ToolAnnotations {
+	public static final field Companion Lio/modelcontextprotocol/kotlin/sdk/ToolAnnotations$Companion;
+	public fun <init> (Ljava/lang/String;Ljava/lang/Boolean;Ljava/lang/Boolean;Ljava/lang/Boolean;Ljava/lang/Boolean;)V
+	public synthetic fun <init> (Ljava/lang/String;Ljava/lang/Boolean;Ljava/lang/Boolean;Ljava/lang/Boolean;Ljava/lang/Boolean;ILkotlin/jvm/internal/DefaultConstructorMarker;)V
+	public final fun component1 ()Ljava/lang/String;
+	public final fun component2 ()Ljava/lang/Boolean;
+	public final fun component3 ()Ljava/lang/Boolean;
+	public final fun component4 ()Ljava/lang/Boolean;
+	public final fun component5 ()Ljava/lang/Boolean;
+	public final fun copy (Ljava/lang/String;Ljava/lang/Boolean;Ljava/lang/Boolean;Ljava/lang/Boolean;Ljava/lang/Boolean;)Lio/modelcontextprotocol/kotlin/sdk/ToolAnnotations;
+	public static synthetic fun copy$default (Lio/modelcontextprotocol/kotlin/sdk/ToolAnnotations;Ljava/lang/String;Ljava/lang/Boolean;Ljava/lang/Boolean;Ljava/lang/Boolean;Ljava/lang/Boolean;ILjava/lang/Object;)Lio/modelcontextprotocol/kotlin/sdk/ToolAnnotations;
+	public fun equals (Ljava/lang/Object;)Z
+	public final fun getDestructiveHint ()Ljava/lang/Boolean;
+	public final fun getIdempotentHint ()Ljava/lang/Boolean;
+	public final fun getOpenWorldHint ()Ljava/lang/Boolean;
+	public final fun getReadOnlyHint ()Ljava/lang/Boolean;
+	public final fun getTitle ()Ljava/lang/String;
+	public fun hashCode ()I
+	public fun toString ()Ljava/lang/String;
+}
+
+public synthetic class io/modelcontextprotocol/kotlin/sdk/ToolAnnotations$$serializer : kotlinx/serialization/internal/GeneratedSerializer {
+	public static final field INSTANCE Lio/modelcontextprotocol/kotlin/sdk/ToolAnnotations$$serializer;
+	public final fun childSerializers ()[Lkotlinx/serialization/KSerializer;
+	public final fun deserialize (Lkotlinx/serialization/encoding/Decoder;)Lio/modelcontextprotocol/kotlin/sdk/ToolAnnotations;
+	public synthetic fun deserialize (Lkotlinx/serialization/encoding/Decoder;)Ljava/lang/Object;
+	public final fun getDescriptor ()Lkotlinx/serialization/descriptors/SerialDescriptor;
+	public final fun serialize (Lkotlinx/serialization/encoding/Encoder;Lio/modelcontextprotocol/kotlin/sdk/ToolAnnotations;)V
+	public synthetic fun serialize (Lkotlinx/serialization/encoding/Encoder;Ljava/lang/Object;)V
+	public fun typeParametersSerializers ()[Lkotlinx/serialization/KSerializer;
+}
+
+public final class io/modelcontextprotocol/kotlin/sdk/ToolAnnotations$Companion {
+	public final fun serializer ()Lkotlinx/serialization/KSerializer;
+}
+
 public final class io/modelcontextprotocol/kotlin/sdk/ToolListChangedNotification : io/modelcontextprotocol/kotlin/sdk/ServerNotification {
 	public static final field Companion Lio/modelcontextprotocol/kotlin/sdk/ToolListChangedNotification$Companion;
 	public fun <init> ()V
@@ -2778,8 +2855,8 @@ public class io/modelcontextprotocol/kotlin/sdk/server/Server : io/modelcontextp
 	public final fun addResource (Ljava/lang/String;Ljava/lang/String;Ljava/lang/String;Ljava/lang/String;Lkotlin/jvm/functions/Function2;)V
 	public static synthetic fun addResource$default (Lio/modelcontextprotocol/kotlin/sdk/server/Server;Ljava/lang/String;Ljava/lang/String;Ljava/lang/String;Ljava/lang/String;Lkotlin/jvm/functions/Function2;ILjava/lang/Object;)V
 	public final fun addResources (Ljava/util/List;)V
-	public final fun addTool (Ljava/lang/String;Ljava/lang/String;Lio/modelcontextprotocol/kotlin/sdk/Tool$Input;Lkotlin/jvm/functions/Function2;)V
-	public static synthetic fun addTool$default (Lio/modelcontextprotocol/kotlin/sdk/server/Server;Ljava/lang/String;Ljava/lang/String;Lio/modelcontextprotocol/kotlin/sdk/Tool$Input;Lkotlin/jvm/functions/Function2;ILjava/lang/Object;)V
+	public final fun addTool (Ljava/lang/String;Ljava/lang/String;Lio/modelcontextprotocol/kotlin/sdk/Tool$Input;Lio/modelcontextprotocol/kotlin/sdk/ToolAnnotations;Lkotlin/jvm/functions/Function2;)V
+	public static synthetic fun addTool$default (Lio/modelcontextprotocol/kotlin/sdk/server/Server;Ljava/lang/String;Ljava/lang/String;Lio/modelcontextprotocol/kotlin/sdk/Tool$Input;Lio/modelcontextprotocol/kotlin/sdk/ToolAnnotations;Lkotlin/jvm/functions/Function2;ILjava/lang/Object;)V
 	public final fun addTools (Ljava/util/List;)V
 	protected fun assertCapabilityForMethod (Lio/modelcontextprotocol/kotlin/sdk/Method;)V
 	protected fun assertNotificationCapability (Lio/modelcontextprotocol/kotlin/sdk/Method;)V
diff --git a/src/commonMain/kotlin/io/modelcontextprotocol/kotlin/sdk/server/Server.kt b/src/commonMain/kotlin/io/modelcontextprotocol/kotlin/sdk/server/Server.kt
index e24419e..f5a603c 100644
--- a/src/commonMain/kotlin/io/modelcontextprotocol/kotlin/sdk/server/Server.kt
+++ b/src/commonMain/kotlin/io/modelcontextprotocol/kotlin/sdk/server/Server.kt
@@ -145,6 +145,7 @@ public open class Server(
         name: String,
         description: String,
         inputSchema: Tool.Input = Tool.Input(),
+        toolAnnotations: ToolAnnotations? = null,
         handler: suspend (CallToolRequest) -> CallToolResult
     ) {
         if (capabilities.tools == null) {
@@ -152,7 +153,7 @@ public open class Server(
             throw IllegalStateException("Server does not support tools capability. Enable it in ServerOptions.")
         }
         logger.info { "Registering tool: $name" }
-        tools[name] = RegisteredTool(Tool(name, description, inputSchema), handler)
+        tools[name] = RegisteredTool(Tool(name, description, inputSchema, toolAnnotations), handler)
     }
 
     /**
diff --git a/src/commonMain/kotlin/io/modelcontextprotocol/kotlin/sdk/types.kt b/src/commonMain/kotlin/io/modelcontextprotocol/kotlin/sdk/types.kt
index c5e5456..e70bb96 100644
--- a/src/commonMain/kotlin/io/modelcontextprotocol/kotlin/sdk/types.kt
+++ b/src/commonMain/kotlin/io/modelcontextprotocol/kotlin/sdk/types.kt
@@ -993,6 +993,58 @@ public class PromptListChangedNotification : ServerNotification {
 }
 
 /* Tools */
+/**
+ * Additional properties describing a Tool to clients.
+ *
+ * NOTE: all properties in ToolAnnotations are **hints**.
+ * They are not guaranteed to provide a faithful description of
+ * tool behavior (including descriptive properties like `title`).
+ *
+ * Clients should never make tool use decisions based on ToolAnnotations
+ * received from untrusted servers.
+ */
+@Serializable
+public data class ToolAnnotations(
+    /**
+     * A human-readable title for the tool.
+     */
+    val title: String?,
+    /**
+     * If true, the tool does not modify its environment.
+     *
+     * Default: false
+     */
+    val readOnlyHint: Boolean? = false,
+    /**
+     * If true, the tool may perform destructive updates to its environment.
+     * If false, the tool performs only additive updates.
+     *
+     * (This property is meaningful only when `readOnlyHint == false`)
+     *
+     * Default: true
+     */
+    val destructiveHint: Boolean? = true,
+    /**
+     * If true, calling the tool repeatedly with the same arguments
+     * will have no additional effect on the its environment.
+     *
+     * (This property is meaningful only when `readOnlyHint == false`)
+     *
+     * Default: false
+     */
+    val idempotentHint: Boolean? = false,
+    /**
+     * If true, this tool may interact with an "open world" of external
+     * entities. If false, the tool's domain of interaction is closed.
+     * For example, the world of a web search tool is open, whereas that
+     * of a memory tool is not.
+     *
+     * Default: true
+     */
+    val openWorldHint: Boolean? = true,
+)
+
+
 /**
  * Definition for a tool the client can call.
  */
@@ -1010,6 +1062,11 @@ public data class Tool(
      * A JSON object defining the expected parameters for the tool.
      */
     val inputSchema: Input,
+
+    /**
+     * Optional additional tool information.
+     */
+    val annotations: ToolAnnotations?,
 ) {
     @Serializable
     public data class Input(
diff --git a/src/commonTest/kotlin/ToolSerializationTest.kt b/src/commonTest/kotlin/ToolSerializationTest.kt
index 90c5c10..cc32290 100644
--- a/src/commonTest/kotlin/ToolSerializationTest.kt
+++ b/src/commonTest/kotlin/ToolSerializationTest.kt
@@ -2,6 +2,7 @@ package io.modelcontextprotocol.kotlin.sdk
 
 import io.kotest.assertions.json.shouldEqualJson
 import io.modelcontextprotocol.kotlin.sdk.shared.McpJson
+import kotlinx.atomicfu.atomicArrayOfNulls
 import kotlinx.serialization.encodeToString
 import kotlinx.serialization.json.JsonPrimitive
 import kotlinx.serialization.json.buildJsonObject
@@ -32,6 +33,7 @@ class ToolSerializationTest {
     val getWeatherTool = Tool(
         name = "get_weather",
         description = "Get the current weather in a given location",
+        annotations = null,
         inputSchema = Tool.Input(
             properties = buildJsonObject {
                 put("location", buildJsonObject {
diff --git a/src/jvmTest/kotlin/client/ClientTest.kt b/src/jvmTest/kotlin/client/ClientTest.kt
index 4630a34..88d97eb 100644
--- a/src/jvmTest/kotlin/client/ClientTest.kt
+++ b/src/jvmTest/kotlin/client/ClientTest.kt
@@ -580,6 +580,7 @@ class ClientTest {
                 Tool(
                     name = "testTool",
                     description = "testTool description",
+                    annotations = null,
                     inputSchema = Tool.Input()
                 )
             ), nextCursor = null