feat(py): add mcp plugin and tests

py/packages/genkit/src/genkit/ai/_registry.py

@@ -686,19 +686,47 @@ async def prompt(
 
     def define_resource(
         self,
-        opts: 'ResourceOptions',
-        fn: 'ResourceFn',
+        opts: 'ResourceOptions | None' = None,
+        fn: 'ResourceFn | None' = None,
+        *,
+        name: str | None = None,
+        uri: str | None = None,
+        template: str | None = None,
+        description: str | None = None,
+        metadata: dict[str, Any] | None = None,
     ) -> Action:
         """Define a resource action.
 
         Args:
             opts: Options defining the resource (e.g. uri, template, name).
             fn: Function implementing the resource behavior.
+            name: Optional name for the resource.
+            uri: Optional URI for the resource.
+            template: Optional URI template for the resource.
+            description: Optional description for the resource.
+            metadata: Optional metadata for the resource.
 
         Returns:
             The registered Action for the resource.
         """
-        from genkit.blocks.resource import define_resource as define_resource_block
+        from genkit.blocks.resource import (
+            define_resource as define_resource_block,
+        )
+
+        if fn is None:
+            raise ValueError("A function `fn` must be provided to define a resource.")
+        if opts is None:
+            opts = {}
+        if name:
+            opts['name'] = name
+        if uri:
+            opts['uri'] = uri
+        if template:
+            opts['template'] = template
+        if description:
+            opts['description'] = description
+        if metadata:
+            opts['metadata'] = metadata
 
         return define_resource_block(self.registry, opts, fn)
 

py/packages/genkit/src/genkit/blocks/prompt.py

@@ -794,7 +794,7 @@ async def render_message_prompt(
         resolved = await ensure_async(options.messages)(input, context)
         return resolved
 
-    raise TypeError(f"Unsupported type for messages: {type(options.messages)}")
+    raise TypeError(f'Unsupported type for messages: {type(options.messages)}')
 
 
 async def render_user_prompt(

py/packages/genkit/src/genkit/blocks/resource.py

@@ -1,4 +1,4 @@
-# Copyright 2025 Google LLC
+# Copyright 2026 Google LLC
 #
 # Licensed under the Apache License, Version 2.0 (the "License");
 # you may not use this file except in compliance with the License.
@@ -21,12 +21,14 @@
 and return content (`ResourceOutput`) containing `Part`s.
 """
 
+import inspect
 import re
 from collections.abc import Awaitable, Callable
-from typing import Any, Callable, Protocol, TypedDict
+from typing import Any, Protocol, TypedDict
 
 from pydantic import BaseModel
 
+from genkit.aio import ensure_async
 from genkit.core.action import Action, ActionRunContext
 from genkit.core.action.types import ActionKind
 from genkit.core.registry import Registry
@@ -35,6 +37,7 @@
 
 class ResourceOptions(TypedDict, total=False):
     """Options for defining a resource.
+
     Attributes:
         name: Resource name. If not specified, uri or template will be used as name.
         uri: The URI of the resource. Can contain template variables for simple matches,
@@ -54,6 +57,7 @@ class ResourceOptions(TypedDict, total=False):
 
 class ResourceInput(BaseModel):
     """Input structure for a resource request.
+
     Attributes:
         uri: The full URI being requested/resolved.
     """
@@ -63,6 +67,7 @@ class ResourceInput(BaseModel):
 
 class ResourceOutput(BaseModel):
     """Output structure from a resource resolution.
+
     Attributes:
         content: A list of `Part` objects representing the resource content.
     """
@@ -84,12 +89,15 @@ def __call__(self, input: ResourceInput, ctx: ActionRunContext) -> Awaitable[Res
 
 async def resolve_resources(registry: Registry, resources: list[ResourceArgument] | None = None) -> list[Action]:
     """Resolves a list of resource names or actions into a list of Action objects.
+
     Args:
         registry: The registry to lookup resources in.
         resources: A list of resource references, which can be either direct `Action`
                    objects or strings (names/URIs).
+
     Returns:
         A list of resolved `Action` objects.
+
     Raises:
         ValueError: If a resource reference is invalid or cannot be found.
     """
@@ -111,11 +119,14 @@ async def lookup_resource_by_name(registry: Registry, name: str) -> Action:
     """Looks up a resource action by name in the registry.
     Tries to resolve the name directly, or with common prefixes like `/resource/`
     or `/dynamic-action-provider/`.
+
     Args:
         registry: The registry to search.
         name: The name or URI of the resource to lookup.
+
     Returns:
         The found `Action`.
+
     Raises:
         ValueError: If the resource cannot be found.
     """
@@ -133,10 +144,12 @@ def define_resource(registry: Registry, opts: ResourceOptions, fn: ResourceFn) -
     """Defines a resource and registers it with the given registry.
     This creates a resource action that can handle requests for a specific URI
     or URI template.
+
     Args:
         registry: The registry to register the resource with.
         opts: Options defining the resource (name, uri, template, etc.).
         fn: The function that implements resource content retrieval.
+
     Returns:
         The registered `Action` for the resource.
     """
@@ -156,9 +169,11 @@ def resource(opts: ResourceOptions, fn: ResourceFn) -> Action:
     """Defines a dynamic resource action without immediate registration.
     This is an alias for `dynamic_resource`. Useful for defining resources that
     might be registered later or used as standalone actions.
+
     Args:
         opts: Options defining the resource.
         fn: The resource implementation function.
+
     Returns:
         The created `Action`.
     """
@@ -172,11 +187,14 @@ def dynamic_resource(opts: ResourceOptions, fn: ResourceFn) -> Action:
     1. Input validation and matching against the URI/Template.
     2. Execution of the resource function.
     3. Post-processing of output to attach metadata (like parent resource info).
+
     Args:
         opts: Options including `uri` or `template` for matching.
         fn: The function performing the resource retrieval.
+
     Returns:
         An `Action` configured as a resource.
+
     Raises:
         ValueError: If neither `uri` nor `template` is provided in options.
     """
@@ -195,7 +213,16 @@ async def wrapped_fn(input_data: ResourceInput, ctx: ActionRunContext) -> Resour
             if not template_match:
                 raise ValueError(f'input {input_data} did not match template {uri}')
 
-            parts = await fn(input_data, ctx)
+            sig = inspect.signature(fn)
+            afn = ensure_async(fn)
+            n_params = len(sig.parameters)
+
+            if n_params == 0:
+                parts = await afn()
+            elif n_params == 1:
+                parts = await afn(input_data)
+            else:
+                parts = await afn(input_data, ctx)
 
             # Post-processing parts to add metadata
             content_list = parts.content if hasattr(parts, 'content') else parts.get('content', [])
@@ -237,7 +264,7 @@ async def wrapped_fn(input_data: ResourceInput, ctx: ActionRunContext) -> Resour
                     parts['content'] = [p.model_dump() if isinstance(p, BaseModel) else p for p in parts['content']]
                 return parts
             return parts
-        except Exception as e:
+        except Exception:
             raise
 
     name = opts.get('name') or uri
@@ -262,9 +289,11 @@ async def wrapped_fn(input_data: ResourceInput, ctx: ActionRunContext) -> Resour
 
 def create_matcher(uri: str | None, template: str | None) -> Callable[[ResourceInput], bool]:
     """Creates a matching function for resource validation.
+
     Args:
         uri: Optional fixed URI string.
         template: Optional URI template string.
+
     Returns:
         A callable that takes ResourceInput and returns True if it matches.
     """
@@ -281,8 +310,10 @@ def matcher(input_data: ResourceInput) -> bool:
 
 def is_dynamic_resource_action(action: Action) -> bool:
     """Checks if an action is a dynamic resource (not registered).
+
     Args:
         action: The action to check.
+
     Returns:
         True if the action is a dynamic resource, False otherwise.
     """
@@ -334,10 +365,12 @@ async def find_matching_resource(
 ) -> Action | None:
     """Finds a matching resource action.
     Checks dynamic resources first, then the registry.
+
     Args:
         registry: The registry to search.
         dynamic_resources: Optional list of dynamic resource actions to check first.
         input_data: The resource input containing the URI matched against.
+
     Returns:
         The matching Action or None.
     """
@@ -351,8 +384,6 @@ async def find_matching_resource(
     if resource:
         return resource
 
-    # Iterate all resources to check for matches (e.g. templates)
-    # This is less efficient but necessary for template matching if not optimized
     # Iterate all resources to check for matches (e.g. templates)
     # This is less efficient but necessary for template matching if not optimized
     resources = registry.get_actions_by_kind(ActionKind.RESOURCE) if hasattr(registry, 'get_actions_by_kind') else {}

py/packages/genkit/tests/genkit/veneer/resource_test.py

@@ -1,4 +1,4 @@
-# Copyright 2025 Google LLC
+# Copyright 2026 Google LLC
 #
 # Licensed under the Apache License, Version 2.0 (the "License");
 # you may not use this file except in compliance with the License.

py/packages/genkit/tests/genkit/veneer/veneer_test.py

@@ -1,6 +1,6 @@
 #!/usr/bin/env python3
 #
-# Copyright 2025 Google LLC
+# Copyright 2026 Google LLC
 # SPDX-License-Identifier: Apache-2.0
 
 """Tests for the action module."""

py/plugins/mcp/README.md

@@ -0,0 +1,3 @@
+# Genkit MCP Plugin
+
+Integrate Model Context Protocol (MCP) with Genkit.

py/plugins/mcp/examples/client/simple_client.py

@@ -0,0 +1,53 @@
+# Copyright 2025 Google LLC
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+#
+# SPDX-License-Identifier: Apache-2.0
+
+import asyncio
+
+from genkit.ai import Genkit
+from genkit.plugins.mcp import McpServerConfig, create_mcp_client
+
+try:
+    from genkit.plugins.google_genai import GoogleAI
+except ImportError:
+    GoogleAI = None
+
+
+# Simple client example connecting to 'everything' server using npx
+async def main():
+    # Define the client plugin
+    everything_client = create_mcp_client(
+        name='everything', config=McpServerConfig(command='npx', args=['-y', '@modelcontextprotocol/server-everything'])
+    )
+
+    plugins = [everything_client]
+    if GoogleAI:
+        plugins.append(GoogleAI())
+
+    ai = Genkit(plugins=plugins)
+
+    await everything_client.connect()
+
+    print('Connected! Listing tools...')
+
+    tools = await everything_client.list_tools()
+    for t in tools:
+        print(f'- {t.name}: {t.description}')
+
+    await everything_client.close()
+
+
+if __name__ == '__main__':
+    asyncio.run(main())

py/plugins/mcp/examples/server/prompts/port_code.prompt

@@ -0,0 +1,13 @@
+---
+input:
+  schema:
+    code: string, the source code to port from one language to another
+    fromLang?: string, the original language of the source code (e.g. js, python)
+    toLang: string, the destination language of the source code (e.g. python, js)
+---
+
+You are assisting the user in translating code between two programming languages. Given the code below, translate it into {{toLang}}.
+
+```{{#if fromLang}}{{fromLang}}{{/if}}
+{{code}}
+```

py/plugins/mcp/examples/server/simple_server.py

@@ -0,0 +1,63 @@
+# Copyright 2026 Google LLC
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+#
+# SPDX-License-Identifier: Apache-2.0
+
+import asyncio
+
+from pydantic import BaseModel, Field
+
+from genkit.ai import Genkit
+from genkit.plugins.mcp import McpServerOptions, create_mcp_server
+
+
+# Define input model
+class AddInput(BaseModel):
+    a: int = Field(..., description='First number')
+    b: int = Field(..., description='Second number')
+
+
+import os
+
+
+def main():
+    # Load prompts from the 'prompts' directory relative to this script
+    script_dir = os.path.dirname(os.path.abspath(__file__))
+    prompts_dir = os.path.join(script_dir, 'prompts')
+
+    ai = Genkit(prompt_dir=prompts_dir)
+
+    @ai.tool(name='add', description='add two numbers together')
+    def add(input: AddInput):
+        return input.a + input.b
+
+    # Genkit Python prompt definition (simplified)
+    # Note: In Python, prompts are typically loaded from files via prompt_dir
+    # This inline definition is for demonstration purposes
+    happy_prompt = ai.define_prompt(
+        input_schema={'action': str},
+        prompt="If you're happy and you know it, {{action}}.",
+    )
+
+    # Create and start MCP server
+    # Note: create_mcp_server returns McpServer instance.
+    # In JS example: .start() is called.
+    server = create_mcp_server(ai, McpServerOptions(name='example_server', version='0.0.1'))
+
+    print('Starting MCP server on stdio...')
+    asyncio.run(server.start())
+
+
+if __name__ == '__main__':
+    main()