Add icons support for ResourceTemplate

This change adds icons metadata support to ResourceTemplate, bringing
it in line with Resource, Tool, and Prompt types. The MCP specification
was updated to include icons for ResourceTemplate, and this implements
that feature in the Python SDK.

Changes:
- Add icons field to ResourceTemplate type definition
- Update ResourceTemplate class to store and pass icons
- Update resource_manager to accept icons parameter
- Update FastMCP server to expose icons in list_resource_templates
- Add test coverage for resource template icons

All primitives (tools, resources, prompts, resource templates) now
consistently support icons metadata.

Author: pja-ant

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

@@ -61,6 +61,7 @@ def add_template(
         title: str | None = None,
         description: str | None = None,
         mime_type: str | None = None,
+        icons: list[Any] | None = None,
     ) -> ResourceTemplate:
         """Add a template from a function."""
         template = ResourceTemplate.from_function(
@@ -70,6 +71,7 @@ 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."""