Merge branch 'modelcontextprotocol:main' into main

Author: DebajitKumarPhukan

.github/CODEOWNERS

@@ -516,6 +516,41 @@ def debug_error(error: str) -> list[base.Message]:
 _Full example: [examples/snippets/servers/basic_prompt.py](https://github.com/modelcontextprotocol/python-sdk/blob/main/examples/snippets/servers/basic_prompt.py)_
 <!-- /snippet-source -->
 
+### Icons
+
+MCP servers can provide icons for UI display. Icons can be added to the server implementation, tools, resources, and prompts:
+
+```python
+from mcp.server.fastmcp import FastMCP, Icon
+
+# Create an icon from a file path or URL
+icon = Icon(
+    src="icon.png",
+    mimeType="image/png",
+    sizes="64x64"
+)
+
+# Add icons to server
+mcp = FastMCP(
+    "My Server",
+    website_url="https://example.com",
+    icons=[icon]
+)
+
+# Add icons to tools, resources, and prompts
+@mcp.tool(icons=[icon])
+def my_tool():
+    """Tool with an icon."""
+    return "result"
+
+@mcp.resource("demo://resource", icons=[icon])
+def my_resource():
+    """Resource with an icon."""
+    return "content"
+```
+
+_Full example: [examples/fastmcp/icons_demo.py](https://github.com/modelcontextprotocol/python-sdk/blob/main/examples/fastmcp/icons_demo.py)_
+
 ### Images
 
 FastMCP provides an `Image` class that automatically handles image data:
@@ -747,6 +782,8 @@ async def book_table(date: str, time: str, party_size: int, ctx: Context[ServerS
 _Full example: [examples/snippets/servers/elicitation.py](https://github.com/modelcontextprotocol/python-sdk/blob/main/examples/snippets/servers/elicitation.py)_
 <!-- /snippet-source -->
 
+Elicitation schemas support default values for all field types. Default values are automatically included in the JSON schema sent to clients, allowing them to pre-populate forms.
+
 The `elicit()` method returns an `ElicitationResult` with:
 
 - `action`: "accept", "decline", or "cancel"
@@ -896,6 +933,8 @@ The FastMCP server instance accessible via `ctx.fastmcp` provides access to serv
 
 - `ctx.fastmcp.name` - The server's name as defined during initialization
 - `ctx.fastmcp.instructions` - Server instructions/description provided to clients
+- `ctx.fastmcp.website_url` - Optional website URL for the server
+- `ctx.fastmcp.icons` - Optional list of icons for UI display
 - `ctx.fastmcp.settings` - Complete server configuration object containing:
   - `debug` - Debug mode flag
   - `log_level` - Current logging level

README.md

@@ -291,8 +291,15 @@ async def process_llm_response(self, llm_response: str) -> str:
         """
         import json
 
+        def _clean_json_string(json_string: str) -> str:
+            """Remove ```json ... ``` or ``` ... ``` wrappers if the LLM response is fenced."""
+            import re
+
+            pattern = r"^```(?:\s*json)?\s*(.*?)\s*```$"
+            return re.sub(pattern, r"\1", json_string, flags=re.DOTALL | re.IGNORECASE).strip()
+
         try:
-            tool_call = json.loads(llm_response)
+            tool_call = json.loads(_clean_json_string(llm_response))
             if "tool" in tool_call and "arguments" in tool_call:
                 logging.info(f"Executing tool: {tool_call['tool']}")
                 logging.info(f"With arguments: {tool_call['arguments']}")

examples/clients/simple-chatbot/mcp_simple_chatbot/main.py

@@ -0,0 +1,55 @@
+"""
+FastMCP Icons Demo Server
+
+Demonstrates using icons with tools, resources, prompts, and implementation.
+"""
+
+import base64
+from pathlib import Path
+
+from mcp.server.fastmcp import FastMCP, Icon
+
+# Load the icon file and convert to data URI
+icon_path = Path(__file__).parent / "mcp.png"
+icon_data = base64.standard_b64encode(icon_path.read_bytes()).decode()
+icon_data_uri = f"data:image/png;base64,{icon_data}"
+
+icon_data = Icon(src=icon_data_uri, mimeType="image/png", sizes=["64x64"])
+
+# Create server with icons in implementation
+mcp = FastMCP("Icons Demo Server", website_url="https://github.com/modelcontextprotocol/python-sdk", icons=[icon_data])
+
+
+@mcp.tool(icons=[icon_data])
+def demo_tool(message: str) -> str:
+    """A demo tool with an icon."""
+    return message
+
+
+@mcp.resource("demo://readme", icons=[icon_data])
+def readme_resource() -> str:
+    """A demo resource with an icon"""
+    return "This resource has an icon"
+
+
+@mcp.prompt("prompt_with_icon", icons=[icon_data])
+def prompt_with_icon(text: str) -> str:
+    """A demo prompt with an icon"""
+    return text
+
+
+@mcp.tool(
+    icons=[
+        Icon(src=icon_data_uri, mimeType="image/png", sizes=["16x16"]),
+        Icon(src=icon_data_uri, mimeType="image/png", sizes=["32x32"]),
+        Icon(src=icon_data_uri, mimeType="image/png", sizes=["64x64"]),
+    ]
+)
+def multi_icon_tool(action: str) -> str:
+    """A tool demonstrating multiple icons."""
+    return "multi_icon_tool"
+
+
+if __name__ == "__main__":
+    # Run the server
+    mcp.run()

examples/fastmcp/icons_demo.py

@@ -8,6 +8,7 @@
 from anyio.abc import TaskStatus
 from anyio.streams.memory import MemoryObjectReceiveStream, MemoryObjectSendStream
 from httpx_sse import aconnect_sse
+from httpx_sse._exceptions import SSEError
 
 import mcp.types as types
 from mcp.shared._httpx_utils import McpHttpClientFactory, create_mcp_http_client
@@ -106,6 +107,9 @@ async def sse_reader(
                                         await read_stream_writer.send(session_message)
                                     case _:
                                         logger.warning(f"Unknown SSE event: {sse.event}")
+                        except SSEError as sse_exc:
+                            logger.exception("Encountered SSE exception")
+                            raise sse_exc
                         except Exception as exc:
                             logger.exception("Error in sse_reader")
                             await read_stream_writer.send(exc)

examples/fastmcp/mcp.png

@@ -154,6 +154,7 @@ async def stdout_reader():
                         try:
                             message = types.JSONRPCMessage.model_validate_json(line)
                         except Exception as exc:
+                            logger.exception("Failed to parse JSONRPC message from server")
                             await read_stream_writer.send(exc)
                             continue
 

src/mcp/client/sse.py

@@ -68,7 +68,7 @@ async def handle(self, request: Request) -> Response:
                     ),
                     status_code=400,
                 )
-        if set(client_metadata.grant_types) != {"authorization_code", "refresh_token"}:
+        if not {"authorization_code", "refresh_token"}.issubset(set(client_metadata.grant_types)):
             return PydanticJSONResponse(
                 content=RegistrationErrorResponse(
                     error="invalid_client_metadata",
@@ -77,6 +77,17 @@ async def handle(self, request: Request) -> Response:
                 status_code=400,
             )
 
+        # The MCP spec requires servers to use the authorization `code` flow
+        # with PKCE
+        if "code" not in client_metadata.response_types:
+            return PydanticJSONResponse(
+                content=RegistrationErrorResponse(
+                    error="invalid_client_metadata",
+                    error_description="response_types must include 'code' for authorization_code grant",
+                ),
+                status_code=400,
+            )
+
         client_id_issued_at = int(time.time())
         client_secret_expires_at = (
             client_id_issued_at + self.options.client_secret_expiry_seconds

src/mcp/client/stdio/__init__.py

@@ -2,8 +2,10 @@
 
 from importlib.metadata import version
 
+from mcp.types import Icon
+
 from .server import Context, FastMCP
 from .utilities.types import Audio, Image
 
 __version__ = version("mcp")
-__all__ = ["FastMCP", "Context", "Image", "Audio"]
+__all__ = ["FastMCP", "Context", "Image", "Audio", "Icon"]

src/mcp/server/auth/handlers/register.py

@@ -11,7 +11,7 @@
 
 from mcp.server.fastmcp.utilities.context_injection import find_context_parameter, inject_context
 from mcp.server.fastmcp.utilities.func_metadata import func_metadata
-from mcp.types import ContentBlock, TextContent
+from mcp.types import ContentBlock, Icon, TextContent
 
 if TYPE_CHECKING:
     from mcp.server.fastmcp.server import Context
@@ -71,6 +71,7 @@ class Prompt(BaseModel):
     description: str | None = Field(None, description="Description of what the prompt does")
     arguments: list[PromptArgument] | None = Field(None, description="Arguments that can be passed to the prompt")
     fn: Callable[..., PromptResult | Awaitable[PromptResult]] = Field(exclude=True)
+    icons: list[Icon] | None = Field(default=None, description="Optional list of icons for this prompt")
     context_kwarg: str | None = Field(None, description="Name of the kwarg that should receive context", exclude=True)
 
     @classmethod
@@ -80,6 +81,7 @@ def from_function(
         name: str | None = None,
         title: str | None = None,
         description: str | None = None,
+        icons: list[Icon] | None = None,
         context_kwarg: str | None = None,
     ) -> Prompt:
         """Create a Prompt from a function.
@@ -128,6 +130,7 @@ def from_function(
             description=description or fn.__doc__ or "",
             arguments=arguments,
             fn=fn,
+            icons=icons,
             context_kwarg=context_kwarg,
         )