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36876c5148Co-authored-by: marvin-context-protocol[bot] <225465937+marvin-context-protocol[bot]@users.noreply.github.com>
186 lines
6.4 KiB
Text
186 lines
6.4 KiB
Text
---
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title: run
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sidebarTitle: run
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---
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# `fastmcp.server.sampling.run`
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Sampling types and helper functions for FastMCP servers.
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## Functions
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### `determine_handler_mode` <sup><a href="https://github.com/jlowin/fastmcp/blob/main/src/fastmcp/server/sampling/run.py#L128" target="_blank"><Icon icon="github" style="width: 14px; height: 14px;" /></a></sup>
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```python
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determine_handler_mode(context: Context, needs_tools: bool) -> bool
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```
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Determine whether to use fallback handler or client for sampling.
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**Args:**
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- `context`: The MCP context.
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- `needs_tools`: Whether the sampling request requires tool support.
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**Returns:**
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- True if fallback handler should be used, False to use client.
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**Raises:**
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- `ValueError`: If client lacks required capability and no fallback configured.
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### `call_sampling_handler` <sup><a href="https://github.com/jlowin/fastmcp/blob/main/src/fastmcp/server/sampling/run.py#L187" target="_blank"><Icon icon="github" style="width: 14px; height: 14px;" /></a></sup>
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```python
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call_sampling_handler(context: Context, messages: list[SamplingMessage]) -> CreateMessageResult | CreateMessageResultWithTools
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```
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Make LLM call using the fallback handler.
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Note: This function expects the caller (sample_step) to have validated that
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sampling_handler is set via determine_handler_mode(). The checks below are
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safeguards against internal misuse.
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### `execute_tools` <sup><a href="https://github.com/jlowin/fastmcp/blob/main/src/fastmcp/server/sampling/run.py#L238" target="_blank"><Icon icon="github" style="width: 14px; height: 14px;" /></a></sup>
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```python
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execute_tools(tool_calls: list[ToolUseContent], tool_map: dict[str, SamplingTool], mask_error_details: bool = False) -> list[ToolResultContent]
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```
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Execute tool calls and return results.
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**Args:**
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- `tool_calls`: List of tool use requests from the LLM.
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- `tool_map`: Mapping from tool name to SamplingTool.
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- `mask_error_details`: If True, mask detailed error messages from tool execution.
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When masked, only generic error messages are returned to the LLM.
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Tools can explicitly raise ToolError to bypass masking when they want
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to provide specific error messages to the LLM.
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**Returns:**
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- List of tool result content blocks.
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### `prepare_messages` <sup><a href="https://github.com/jlowin/fastmcp/blob/main/src/fastmcp/server/sampling/run.py#L317" target="_blank"><Icon icon="github" style="width: 14px; height: 14px;" /></a></sup>
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```python
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prepare_messages(messages: str | Sequence[str | SamplingMessage]) -> list[SamplingMessage]
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```
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Convert various message formats to a list of SamplingMessage objects.
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### `prepare_tools` <sup><a href="https://github.com/jlowin/fastmcp/blob/main/src/fastmcp/server/sampling/run.py#L336" target="_blank"><Icon icon="github" style="width: 14px; height: 14px;" /></a></sup>
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```python
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prepare_tools(tools: Sequence[SamplingTool | Callable[..., Any]] | None) -> list[SamplingTool] | None
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```
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Convert tools to SamplingTool objects.
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### `extract_tool_calls` <sup><a href="https://github.com/jlowin/fastmcp/blob/main/src/fastmcp/server/sampling/run.py#L355" target="_blank"><Icon icon="github" style="width: 14px; height: 14px;" /></a></sup>
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```python
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extract_tool_calls(response: CreateMessageResult | CreateMessageResultWithTools) -> list[ToolUseContent]
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```
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Extract tool calls from a response.
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### `create_final_response_tool` <sup><a href="https://github.com/jlowin/fastmcp/blob/main/src/fastmcp/server/sampling/run.py#L367" target="_blank"><Icon icon="github" style="width: 14px; height: 14px;" /></a></sup>
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```python
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create_final_response_tool(result_type: type) -> SamplingTool
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```
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Create a synthetic 'final_response' tool for structured output.
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This tool is used to capture structured responses from the LLM.
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The tool's schema is derived from the result_type.
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### `sample_step_impl` <sup><a href="https://github.com/jlowin/fastmcp/blob/main/src/fastmcp/server/sampling/run.py#L403" target="_blank"><Icon icon="github" style="width: 14px; height: 14px;" /></a></sup>
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```python
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sample_step_impl(context: Context, messages: str | Sequence[str | SamplingMessage]) -> SampleStep
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```
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Implementation of Context.sample_step().
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Make a single LLM sampling call. This is a stateless function that makes
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exactly one LLM call and optionally executes any requested tools.
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### `sample_impl` <sup><a href="https://github.com/jlowin/fastmcp/blob/main/src/fastmcp/server/sampling/run.py#L515" target="_blank"><Icon icon="github" style="width: 14px; height: 14px;" /></a></sup>
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```python
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sample_impl(context: Context, messages: str | Sequence[str | SamplingMessage]) -> SamplingResult[ResultT]
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```
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Implementation of Context.sample().
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Send a sampling request to the client and await the response. This method
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runs to completion automatically, executing a tool loop until the LLM
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provides a final text response.
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## Classes
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### `SamplingResult` <sup><a href="https://github.com/jlowin/fastmcp/blob/main/src/fastmcp/server/sampling/run.py#L50" target="_blank"><Icon icon="github" style="width: 14px; height: 14px;" /></a></sup>
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Result of a sampling operation.
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**Attributes:**
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- `text`: The text representation of the result (raw text or JSON for structured).
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- `result`: The typed result (str for text, parsed object for structured output).
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- `history`: All messages exchanged during sampling.
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### `SampleStep` <sup><a href="https://github.com/jlowin/fastmcp/blob/main/src/fastmcp/server/sampling/run.py#L65" target="_blank"><Icon icon="github" style="width: 14px; height: 14px;" /></a></sup>
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Result of a single sampling call.
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Represents what the LLM returned in this step plus the message history.
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**Methods:**
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#### `is_tool_use` <sup><a href="https://github.com/jlowin/fastmcp/blob/main/src/fastmcp/server/sampling/run.py#L75" target="_blank"><Icon icon="github" style="width: 14px; height: 14px;" /></a></sup>
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```python
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is_tool_use(self) -> bool
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```
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True if the LLM is requesting tool execution.
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#### `text` <sup><a href="https://github.com/jlowin/fastmcp/blob/main/src/fastmcp/server/sampling/run.py#L82" target="_blank"><Icon icon="github" style="width: 14px; height: 14px;" /></a></sup>
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```python
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text(self) -> str | None
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```
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Extract text from the response, if available.
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#### `tool_calls` <sup><a href="https://github.com/jlowin/fastmcp/blob/main/src/fastmcp/server/sampling/run.py#L95" target="_blank"><Icon icon="github" style="width: 14px; height: 14px;" /></a></sup>
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```python
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tool_calls(self) -> list[ToolUseContent]
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```
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Get the list of tool calls from the response.
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