mirror of
https://github.com/PrefectHQ/fastmcp.git
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e32a2098f9fastmcp.types re-exported 29 mcp_types symbols verbatim, which was pointless indirection users had to discover. It now holds only Textarea, the one type FastMCP actually defines; everything else imports from mcp_types directly. These mirrors were added during unreleased SDK v2 migration work and never shipped, so this is not a breaking change.
74 lines
2.1 KiB
Python
74 lines
2.1 KiB
Python
"""Example of custom tool serialization using ToolResult and a wrapper decorator.
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This pattern provides explicit control over how tool outputs are serialized,
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making the serialization visible in each tool's code.
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"""
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import asyncio
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import inspect
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from collections.abc import Callable
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from functools import wraps
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from typing import Any
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import yaml
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from mcp_types import TextContent
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from fastmcp import Client, FastMCP
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from fastmcp.tools import ToolResult
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def with_serializer(serializer: Callable[[Any], str]):
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"""Decorator to apply custom serialization to tool output."""
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def decorator(fn):
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@wraps(fn)
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def wrapper(*args, **kwargs):
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result = fn(*args, **kwargs)
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return ToolResult(content=serializer(result), structured_content=result)
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@wraps(fn)
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async def async_wrapper(*args, **kwargs):
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result = await fn(*args, **kwargs)
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return ToolResult(content=serializer(result), structured_content=result)
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return async_wrapper if inspect.iscoroutinefunction(fn) else wrapper
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return decorator
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# Create reusable serializer decorators
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with_yaml = with_serializer(lambda d: yaml.dump(d, width=100, sort_keys=False))
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server = FastMCP(name="CustomSerializerExample")
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@server.tool
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@with_yaml
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def get_example_data() -> dict:
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"""Returns some example data serialized as YAML."""
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return {"name": "Test", "value": 123, "status": True}
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@server.tool
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def get_json_data() -> dict:
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"""Returns data with default JSON serialization."""
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return {"format": "json", "data": [1, 2, 3]}
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async def example_usage():
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async with Client(server) as client:
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# YAML serialized tool
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yaml_result = await client.call_tool("get_example_data", {})
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print("YAML Tool Result:")
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if yaml_result.content and isinstance(yaml_result.content[0], TextContent):
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print(yaml_result.content[0].text)
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print()
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# Default JSON serialized tool
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json_result = await client.call_tool("get_json_data", {})
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print("JSON Tool Result:")
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print(json_result.data)
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if __name__ == "__main__":
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asyncio.run(example_usage())
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