Let MCPServer.add_prompt take a function; export prompt Message classes

add_tool(fn) registers a function but add_prompt() only took a ready-made Prompt,
so registering a prompt outside the decorator meant importing Prompt from a
subpackage and calling Prompt.from_function yourself. add_prompt() now also
accepts the function with the same keyword options as @prompt(); the Prompt form
(including add_prompt(prompt=...)) is unchanged and @prompt() still hands
add_prompt a Prompt, so subclass overrides keep intercepting registrations.

Message, UserMessage and AssistantMessage are re-exported from
mcp.server.mcpserver next to Image and Audio.

Author: maxisbey

docs/migration.md

@@ -668,7 +668,7 @@ All submodules under `mcp.server.fastmcp.*` are now under `mcp.server.mcpserver.
 
 - `Image`, `Audio` — from `mcp.server.mcpserver` (or `.utilities.types`)
 - `Icon` — from `mcp.server.mcpserver` or `mcp.types` (not a top-level `mcp` export); its `mimeType` field is now `mime_type` per the [snake_case renames](#field-names-changed-from-camelcase-to-snake_case), though the `mimeType=` kwarg still constructs
-- `Message`, `UserMessage`, `AssistantMessage` — from `mcp.server.mcpserver.prompts.base`
+- `Message`, `UserMessage`, `AssistantMessage` — from `mcp.server.mcpserver` (or `.prompts.base`)
 - `ToolError`, `ResourceError` — from `mcp.server.mcpserver.exceptions`
 - `MCPServerError` (renamed from `FastMCPError`) — from `mcp.server.mcpserver.exceptions`
 
@@ -678,7 +678,7 @@ Beyond the changes covered in this section, the everyday `FastMCP` surface carri
 
 - **Decorators.** `@mcp.tool()`, `@mcp.resource()`, `@mcp.prompt()`, and `@mcp.completion()` take the same arguments and handler signatures as v1. The lowlevel [`on_completion` reshape](#lowlevel-server-decorator-based-handlers-replaced-with-constructor-on_-params) applies only to the lowlevel `Server`; a high-level `@mcp.completion()` handler is still called as `(ref, argument, context)`.
 - **Tool return handling.** A returned `CallToolResult` (including an `Annotated[CallToolResult, YourModel]` output schema, and `_meta`) is passed through, `Image` and `Audio` convert to content blocks as before, ready-made content blocks are kept as-is (neither is [structured by default](#content-block-image-and-audio-return-annotations-are-unstructured) now, even inside a `list`), and dict, list, scalar, and model returns are wrapped into `content` and `structured_content` by the same rules.
-- **Listing and registration methods.** `list_tools()`, `list_resources()`, `list_resource_templates()`, and `list_prompts()` return the same lists and are still what the protocol handlers call, so subclass overrides still take effect. `add_tool()`, `add_resource()`, and `add_prompt()` are unchanged.
+- **Listing and registration methods.** `list_tools()`, `list_resources()`, `list_resource_templates()`, and `list_prompts()` return the same lists and are still what the protocol handlers call, so subclass overrides still take effect. `add_tool()`, `add_resource()`, and `add_prompt()` are unchanged (`add_prompt()` additionally accepts the plain function, like `add_tool()`).
 - **Helpers.** `Image.to_image_content()`, `Audio.to_audio_content()`, and the prompt `Message`, `UserMessage`, and `AssistantMessage` classes.
 - **Lifespan.** The `lifespan=` constructor argument and `ctx.request_context.lifespan_context` work as before, and the class is still generic over the lifespan result: `FastMCP[MyState]` becomes `MCPServer[MyState]`. (`Context`'s own type parameters did change; see [`RequestContext` type parameters simplified](#requestcontext-type-parameters-simplified).)
 - **Tool internals.** `Tool`, `Tool.from_function()`, `FuncMetadata`, `ArgModelBase`, and `func_metadata()` keep their v1 shapes; the one change is the now-required `context` argument to `Tool.run()`, described [below](#mcpservercall_tool-read_resource-get_prompt-now-accept-a-context-parameter).

src/mcp/server/mcpserver/__init__.py

@@ -13,6 +13,7 @@
 )
 
 from .context import Context
+from .prompts.base import AssistantMessage, Message, UserMessage
 from .resolve import (
     AcceptedElicitation,
     CancelledElicitation,
@@ -32,6 +33,9 @@
     "Context",
     "Image",
     "Audio",
+    "Message",
+    "UserMessage",
+    "AssistantMessage",
     "Icon",
     "Resolve",
     "Elicit",

src/mcp/server/mcpserver/server.py

@@ -890,12 +890,47 @@ def decorator(fn: _CallableT) -> _CallableT:
 
         return decorator
 
-    def add_prompt(self, prompt: Prompt) -> None:
+    @overload
+    def add_prompt(self, prompt: Prompt) -> None: ...
+
+    @overload
+    def add_prompt(
+        self,
+        fn: Callable[..., Any],
+        /,
+        *,
+        name: str | None = None,
+        title: str | None = None,
+        description: str | None = None,
+        icons: list[Icon] | None = None,
+    ) -> None: ...
+
+    def add_prompt(
+        self,
+        prompt: Prompt | Callable[..., Any],
+        *,
+        name: str | None = None,
+        title: str | None = None,
+        description: str | None = None,
+        icons: list[Icon] | None = None,
+    ) -> None:
         """Add a prompt to the server.
 
+        Pass the function that renders the prompt: its name, docstring and parameters become
+        the prompt's name, description and arguments, exactly as with `@prompt()`. A ready-made
+        `Prompt` instance is registered as-is.
+
         Args:
-            prompt: A Prompt instance to add
+            prompt: The function to register as a prompt, or a `Prompt` instance
+            name: Optional name for the prompt (defaults to the function name)
+            title: Optional human-readable title for the prompt
+            description: Optional description (defaults to the function's docstring)
+            icons: Optional list of icons for the prompt
         """
+        if not isinstance(prompt, Prompt):
+            prompt = Prompt.from_function(prompt, name=name, title=title, description=description, icons=icons)
+        elif any(arg is not None for arg in (name, title, description, icons)):
+            raise TypeError("name, title, description and icons can only be set when registering a function")
         self._prompt_manager.add_prompt(prompt)
 
     def remove_prompt(self, name: str) -> None:

tests/server/mcpserver/test_server.py

@@ -50,6 +50,7 @@
 from mcp.server.mcpserver import Context, MCPServer, ResourceSecurity
 from mcp.server.mcpserver.exceptions import ResourceNotFoundError, ToolError
 from mcp.server.mcpserver.prompts.base import Message, UserMessage
+from mcp.server.mcpserver.prompts.base import Prompt as PromptTemplate  # `Prompt` here is the mcp_types wire model
 from mcp.server.mcpserver.resources import FileResource, FunctionResource
 from mcp.server.mcpserver.utilities.types import Audio, Image
 from mcp.server.subscriptions import (
@@ -2320,6 +2321,46 @@ def test_context_exposes_its_mcp_server() -> None:
     assert Context(mcp_server=mcp).mcp_server is mcp
 
 
+def _greet(who: str) -> str:
+    """Say hi."""
+    return f"hi {who}"
+
+
+async def test_add_prompt_registers_a_function_like_the_decorator() -> None:
+    """SDK-defined: `add_prompt(fn, ...)` derives name, description and arguments as `@prompt()` does."""
+    mcp = MCPServer()
+    mcp.add_prompt(_greet, title="Greeter")
+
+    async with Client(mcp) as client:
+        [listed] = (await client.list_prompts()).prompts
+        result = await client.get_prompt("_greet", {"who": "max"})
+
+    assert (listed.name, listed.title, listed.description) == ("_greet", "Greeter", "Say hi.")
+    assert [arg.name for arg in listed.arguments or []] == ["who"]
+    assert result.messages[0].content == TextContent(type="text", text="hi max")
+
+
+async def test_add_prompt_registers_a_prompt_instance_as_is() -> None:
+    """SDK-defined: a ready-made prompt handed to `add_prompt` (the 2.0 form) is registered exactly as built."""
+    mcp = MCPServer()
+    mcp.add_prompt(prompt=PromptTemplate.from_function(_greet, name="custom"))
+    [listed] = await mcp.list_prompts()
+    assert listed.name == "custom"
+
+
+async def test_add_prompt_rejects_overrides_alongside_a_prompt_instance() -> None:
+    """SDK-defined: the keyword overrides only apply to the function form; passing them alongside a
+    ready-made prompt is rejected rather than silently ignored."""
+    mcp = MCPServer()
+    prompt: Any = PromptTemplate.from_function(_greet)  # Any: the overloads already reject this call statically
+    with pytest.raises(TypeError) as exc_info:
+        mcp.add_prompt(prompt, name="renamed")
+    assert str(exc_info.value) == snapshot(
+        "name, title, description and icons can only be set when registering a function"
+    )
+    assert await mcp.list_prompts() == []
+
+
 def test_remove_prompt_removes_and_unknown_name_raises() -> None:
     mcp = MCPServer()