Felix Weinberger
50 lines
1.5 KiB
Python
50 lines
1.5 KiB
Python
"""Example showing how to handle and return errors from tools."""
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from mcp.server.fastmcp import FastMCP
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from mcp.server.fastmcp.exceptions import ToolError
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from mcp.types import CallToolResult, TextContent
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mcp = FastMCP("Tool Error Handling Example")
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# Option 1: Raise ToolError for expected error conditions.
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# The error message is returned to the client with isError=True.
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@mcp.tool()
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def divide(a: float, b: float) -> float:
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"""Divide two numbers."""
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if b == 0:
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raise ToolError("Cannot divide by zero")
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return a / b
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# Option 2: Unhandled exceptions are automatically caught and
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# converted to error responses with isError=True.
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@mcp.tool()
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def read_config(path: str) -> str:
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"""Read a configuration file."""
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# If this raises FileNotFoundError, the client receives an
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# error response like "Error executing tool read_config: ..."
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with open(path) as f:
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return f.read()
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# Option 3: Return CallToolResult directly for full control
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# over error responses, including custom content.
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@mcp.tool()
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def validate_input(data: str) -> CallToolResult:
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"""Validate input data."""
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errors: list[str] = []
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if len(data) < 3:
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errors.append("Input must be at least 3 characters")
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if not data.isascii():
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errors.append("Input must be ASCII only")
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if errors:
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return CallToolResult(
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content=[TextContent(type="text", text="\n".join(errors))],
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isError=True,
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)
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return CallToolResult(
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content=[TextContent(type="text", text="Validation passed")],
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)
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