Add icons support for ResourceTemplate (modelcontextprotocol#1412)

Author: pja-ant

src/mcp/server/fastmcp/resources/resource_manager.py

@@ -10,6 +10,7 @@
 from mcp.server.fastmcp.resources.base import Resource
 from mcp.server.fastmcp.resources.templates import ResourceTemplate
 from mcp.server.fastmcp.utilities.logging import get_logger
+from mcp.types import Icon
 
 if TYPE_CHECKING:
     from mcp.server.fastmcp.server import Context
@@ -61,6 +62,7 @@ def add_template(
         title: str | None = None,
         description: str | None = None,
         mime_type: str | None = None,
+        icons: list[Icon] | None = None,
     ) -> ResourceTemplate:
         """Add a template from a function."""
         template = ResourceTemplate.from_function(
@@ -70,6 +72,7 @@ def add_template(
             title=title,
             description=description,
             mime_type=mime_type,
+            icons=icons,
         )
         self._templates[template.uri_template] = template
         return template

src/mcp/server/fastmcp/resources/templates.py

@@ -12,6 +12,7 @@
 from mcp.server.fastmcp.resources.types import FunctionResource, Resource
 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 Icon
 
 if TYPE_CHECKING:
     from mcp.server.fastmcp.server import Context
@@ -27,6 +28,7 @@ class ResourceTemplate(BaseModel):
     title: str | None = Field(description="Human-readable title of the resource", default=None)
     description: str | None = Field(description="Description of what the resource does")
     mime_type: str = Field(default="text/plain", description="MIME type of the resource content")
+    icons: list[Icon] | None = Field(default=None, description="Optional list of icons for the resource template")
     fn: Callable[..., Any] = Field(exclude=True)
     parameters: dict[str, Any] = Field(description="JSON schema for function parameters")
     context_kwarg: str | None = Field(None, description="Name of the kwarg that should receive context")
@@ -40,6 +42,7 @@ def from_function(
         title: str | None = None,
         description: str | None = None,
         mime_type: str | None = None,
+        icons: list[Icon] | None = None,
         context_kwarg: str | None = None,
     ) -> ResourceTemplate:
         """Create a template from a function."""
@@ -67,6 +70,7 @@ def from_function(
             title=title,
             description=description or fn.__doc__ or "",
             mime_type=mime_type or "text/plain",
+            icons=icons,
             fn=fn,
             parameters=parameters,
             context_kwarg=context_kwarg,
@@ -103,7 +107,7 @@ async def create_resource(
                 title=self.title,
                 description=self.description,
                 mime_type=self.mime_type,
-                icons=None,  # Resource templates don't support icons
+                icons=self.icons,
                 fn=lambda: result,  # Capture result in closure
             )
         except Exception as e:

src/mcp/server/fastmcp/server.py

@@ -335,6 +335,7 @@ async def list_resource_templates(self) -> list[MCPResourceTemplate]:
                 title=template.title,
                 description=template.description,
                 mimeType=template.mime_type,
+                icons=template.icons,
             )
             for template in templates
         ]
@@ -559,7 +560,7 @@ def decorator(fn: AnyFunction) -> AnyFunction:
                     title=title,
                     description=description,
                     mime_type=mime_type,
-                    # Note: Resource templates don't support icons
+                    icons=icons,
                 )
             else:
                 # Register as regular resource

src/mcp/types.py

@@ -470,6 +470,8 @@ class ResourceTemplate(BaseMetadata):
     The MIME type for all resources that match this template. This should only be
     included if all resources matching this template have the same type.
     """
+    icons: list[Icon] | None = None
+    """An optional list of icons for this resource template."""
     annotations: Annotations | None = None
     meta: dict[str, Any] | None = Field(alias="_meta", default=None)
     """

tests/issues/test_1338_icons_and_metadata.py

@@ -39,6 +39,12 @@ def test_prompt(text: str) -> str:
         """A test prompt with an icon."""
         return text
 
+    # Create resource template with icon
+    @mcp.resource("test://weather/{city}", icons=[test_icon])
+    def test_resource_template(city: str) -> str:
+        """Get weather for a city."""
+        return f"Weather for {city}"
+
     # Test server metadata includes websiteUrl and icons
     assert mcp.name == "TestServer"
     assert mcp.website_url == "https://example.com"
@@ -75,6 +81,16 @@ def test_prompt(text: str) -> str:
     assert len(prompt.icons) == 1
     assert prompt.icons[0].src == test_icon.src
 
+    # Test resource template includes icon
+    templates = await mcp.list_resource_templates()
+    assert len(templates) == 1
+    template = templates[0]
+    assert template.name == "test_resource_template"
+    assert template.uriTemplate == "test://weather/{city}"
+    assert template.icons is not None
+    assert len(template.icons) == 1
+    assert template.icons[0].src == test_icon.src
+
 
 async def test_multiple_icons():
     """Test that multiple icons can be added to tools, resources, and prompts."""