feat: support audio content

Adds support for a distinct AudioContent type as defined in the specification.
This happens to share a structure with ImageContent, but should probably be
distinguished for parity with the specification itself.

Author: LucaButBoring

examples/servers/simple-streamablehttp-stateless/mcp_simple_streamablehttp_stateless/server.py

@@ -43,7 +43,12 @@ def main(
     @app.call_tool()
     async def call_tool(
         name: str, arguments: dict
-    ) -> list[types.TextContent | types.ImageContent | types.EmbeddedResource]:
+    ) -> list[
+        types.TextContent
+        | types.ImageContent
+        | types.AudioContent
+        | types.EmbeddedResource
+    ]:
         ctx = app.request_context
         interval = arguments.get("interval", 1.0)
         count = arguments.get("count", 5)

examples/servers/simple-streamablehttp/mcp_simple_streamablehttp/server.py

@@ -47,7 +47,12 @@ def main(
     @app.call_tool()
     async def call_tool(
         name: str, arguments: dict
-    ) -> list[types.TextContent | types.ImageContent | types.EmbeddedResource]:
+    ) -> list[
+        types.TextContent
+        | types.ImageContent
+        | types.AudioContent
+        | types.EmbeddedResource
+    ]:
         ctx = app.request_context
         interval = arguments.get("interval", 1.0)
         count = arguments.get("count", 5)

examples/servers/simple-tool/mcp_simple_tool/server.py

@@ -7,7 +7,9 @@
 
 async def fetch_website(
     url: str,
-) -> list[types.TextContent | types.ImageContent | types.EmbeddedResource]:
+) -> list[
+    types.TextContent | types.ImageContent | types.AudioContent | types.EmbeddedResource
+]:
     headers = {
         "User-Agent": "MCP Test Server (github.com/modelcontextprotocol/python-sdk)"
     }
@@ -31,7 +33,12 @@ def main(port: int, transport: str) -> int:
     @app.call_tool()
     async def fetch_tool(
         name: str, arguments: dict
-    ) -> list[types.TextContent | types.ImageContent | types.EmbeddedResource]:
+    ) -> list[
+        types.TextContent
+        | types.ImageContent
+        | types.AudioContent
+        | types.EmbeddedResource
+    ]:
         if name != "fetch":
             raise ValueError(f"Unknown tool: {name}")
         if "url" not in arguments:

src/mcp/server/fastmcp/prompts/base.py

@@ -7,9 +7,9 @@
 import pydantic_core
 from pydantic import BaseModel, Field, TypeAdapter, validate_call
 
-from mcp.types import EmbeddedResource, ImageContent, TextContent
+from mcp.types import AudioContent, EmbeddedResource, ImageContent, TextContent
 
-CONTENT_TYPES = TextContent | ImageContent | EmbeddedResource
+CONTENT_TYPES = TextContent | ImageContent | AudioContent | EmbeddedResource
 
 
 class Message(BaseModel):

src/mcp/server/fastmcp/server.py

@@ -52,6 +52,7 @@
 from mcp.shared.context import LifespanContextT, RequestContext
 from mcp.types import (
     AnyFunction,
+    AudioContent,
     EmbeddedResource,
     GetPromptResult,
     ImageContent,
@@ -271,7 +272,7 @@ def get_context(self) -> Context[ServerSession, object]:
 
     async def call_tool(
         self, name: str, arguments: dict[str, Any]
-    ) -> Sequence[TextContent | ImageContent | EmbeddedResource]:
+    ) -> Sequence[TextContent | ImageContent | AudioContent | EmbeddedResource]:
         """Call a tool by name with arguments."""
         context = self.get_context()
         result = await self._tool_manager.call_tool(name, arguments, context=context)
@@ -871,12 +872,12 @@ async def get_prompt(
 
 def _convert_to_content(
     result: Any,
-) -> Sequence[TextContent | ImageContent | EmbeddedResource]:
+) -> Sequence[TextContent | ImageContent | AudioContent | EmbeddedResource]:
     """Convert a result to a sequence of content objects."""
     if result is None:
         return []
 
-    if isinstance(result, TextContent | ImageContent | EmbeddedResource):
+    if isinstance(result, TextContent | ImageContent | AudioContent | EmbeddedResource):
         return [result]
 
     if isinstance(result, Image):

src/mcp/server/lowlevel/server.py

@@ -400,7 +400,10 @@ def decorator(
                 ...,
                 Awaitable[
                     Iterable[
-                        types.TextContent | types.ImageContent | types.EmbeddedResource
+                        types.TextContent
+                        | types.ImageContent
+                        | types.AudioContent
+                        | types.EmbeddedResource
                     ]
                 ],
             ],

src/mcp/types.py

@@ -651,11 +651,26 @@ class ImageContent(BaseModel):
     model_config = ConfigDict(extra="allow")
 
 
+class AudioContent(BaseModel):
+    """Audio content for a message."""
+
+    type: Literal["audio"]
+    data: str
+    """The base64-encoded audio data."""
+    mimeType: str
+    """
+    The MIME type of the audio. Different providers may support different
+    audio types.
+    """
+    annotations: Annotations | None = None
+    model_config = ConfigDict(extra="allow")
+
+
 class SamplingMessage(BaseModel):
     """Describes a message issued to or received from an LLM API."""
 
     role: Role
-    content: TextContent | ImageContent
+    content: TextContent | ImageContent | AudioContent
     model_config = ConfigDict(extra="allow")
 
 
@@ -677,7 +692,7 @@ class PromptMessage(BaseModel):
     """Describes a message returned as part of a prompt."""
 
     role: Role
-    content: TextContent | ImageContent | EmbeddedResource
+    content: TextContent | ImageContent | AudioContent | EmbeddedResource
     model_config = ConfigDict(extra="allow")
 
 
@@ -796,7 +811,7 @@ class CallToolRequest(Request[CallToolRequestParams, Literal["tools/call"]]):
 class CallToolResult(Result):
     """The server's response to a tool call."""
 
-    content: list[TextContent | ImageContent | EmbeddedResource]
+    content: list[TextContent | ImageContent | AudioContent | EmbeddedResource]
     isError: bool = False
 
 
@@ -960,7 +975,7 @@ class CreateMessageResult(Result):
     """The client's response to a sampling/create_message request from the server."""
 
     role: Role
-    content: TextContent | ImageContent
+    content: TextContent | ImageContent | AudioContent
     model: str
     """The name of the model that generated the message."""
     stopReason: StopReason | None = None

tests/issues/test_88_random_error.py

@@ -12,6 +12,7 @@
 from mcp.server.lowlevel import Server
 from mcp.shared.exceptions import McpError
 from mcp.types import (
+    AudioContent,
     EmbeddedResource,
     ImageContent,
     TextContent,
@@ -37,7 +38,7 @@ async def test_notification_validation_error(tmp_path: Path):
     @server.call_tool()
     async def slow_tool(
         name: str, arg
-    ) -> Sequence[TextContent | ImageContent | EmbeddedResource]:
+    ) -> Sequence[TextContent | ImageContent | AudioContent | EmbeddedResource]:
         nonlocal request_count
         request_count += 1
 

tests/server/fastmcp/test_server.py

@@ -16,6 +16,7 @@
     create_connected_server_and_client_session as client_session,
 )
 from mcp.types import (
+    AudioContent,
     BlobResourceContents,
     ImageContent,
     TextContent,
@@ -207,10 +208,11 @@ def image_tool_fn(path: str) -> Image:
     return Image(path)
 
 
-def mixed_content_tool_fn() -> list[TextContent | ImageContent]:
+def mixed_content_tool_fn() -> list[TextContent | ImageContent | AudioContent]:
     return [
         TextContent(type="text", text="Hello"),
         ImageContent(type="image", data="abc", mimeType="image/png"),
+        AudioContent(type="audio", data="def", mimeType="audio/wav"),
     ]
 
 
@@ -312,14 +314,16 @@ async def test_tool_mixed_content(self):
         mcp.add_tool(mixed_content_tool_fn)
         async with client_session(mcp._mcp_server) as client:
             result = await client.call_tool("mixed_content_tool_fn", {})
-            assert len(result.content) == 2
-            content1 = result.content[0]
-            content2 = result.content[1]
+            assert len(result.content) == 3
+            content1, content2, content3 = result.content
             assert isinstance(content1, TextContent)
             assert content1.text == "Hello"
             assert isinstance(content2, ImageContent)
             assert content2.mimeType == "image/png"
             assert content2.data == "abc"
+            assert isinstance(content3, AudioContent)
+            assert content3.mimeType == "audio/wav"
+            assert content3.data == "def"
 
     @pytest.mark.anyio
     async def test_tool_mixed_list_with_image(self, tmp_path: Path):