modelcontextprotocol · LucaButBoring · May 13, 2025 · May 13, 2025 · Jun 12, 2025 · Jul 1, 2025
@@ -33,14 +33,22 @@ Sampling requests use a standardized message format:
     {
       role: "user" | "assistant",
       content: {
-        type: "text" | "image",
+        type: "text" | "image" | "audio" | "resource" | "resource_link",
 
         // For text:
         text?: string,
 
-        // For images:
+        // For images/audio:
         data?: string,             // base64 encoded
-        mimeType?: string
+        mimeType?: string,
+
+        // For resources:
+        resource?: {
+          uri: string,
+          mimeType: string,
+          text?: string,           // for text resources
+          blob?: string            // for blob resources, base64 encoded
+        }
       }
     }
   ],
@@ -70,7 +78,9 @@ The `messages` array contains the conversation history to send to the LLM. Each
 - `role`: Either "user" or "assistant"
 - `content`: The message content, which can be:
   - Text content with a `text` field
-  - Image content with `data` (base64) and `mimeType` fields
+  - Image/audio content with `data` (base64) and `mimeType` fields
+  - An embedded [resource](/docs/concepts/resources)
+  - A [resource](/docs/concepts/resources) link
 
 ### Model preferences
 

@@ -167,6 +167,42 @@ Sampling messages can contain:
 }
 ```
 
+#### Resource Links
+
+A tool **MAY** return links to [Resources](/specification/draft/server/resources), to provide additional context
+or data. In this case, the tool will return a URI that can be subscribed to or fetched by the client:
+
+```json
+{
+  "type": "resource_link",
+  "uri": "file:///project/src/main.rs",
+  "name": "main.rs",
+  "description": "Primary application entry point",
+  "mimeType": "text/x-rust"
+}
+```
+
+<Info>
+  Resource links returned by tools are not guaranteed to appear in the results
+  of a `resources/list` request.
+</Info>
+
+#### Embedded Resources
+
+[Resources](/specification/draft/server/resources) **MAY** be embedded to provide additional context
+or data using a suitable [URI scheme](../server/resources#common-uri-schemes). Servers that use embedded resources **SHOULD** implement the `resources` capability:
+
+```json
+{
+  "type": "resource",
+  "resource": {
+    "uri": "file:///project/src/main.rs",
+    "mimeType": "text/x-rust",
+    "text": "fn main() {\n    println!(\"Hello world!\");\n}"
+  }
+}
+```
+
 ### Model Preferences
 
 Model selection in MCP requires careful abstraction since servers and clients may use

@@ -1036,7 +1036,7 @@ export interface CreateMessageResult extends Result, SamplingMessage {
  */
 export interface SamplingMessage {
   role: Role;
-  content: TextContent | ImageContent | AudioContent;
+  content: ContentBlock;
 }
 
 /**