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fastmcp.server.elicitation

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Functions

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parse_elicit_response_type

Parse response_type into schema and handling configuration. A response type is required; None raises TypeError. Supports multiple syntaxes:
  • dict: {"low": {"title": "..."}} -> single-select titled enum
  • list patterns:
    • [["a", "b"]] -> multi-select untitled
    • [{"low": {...}}] -> multi-select titled
    • ["a", "b"] -> single-select untitled
  • list\[X] type annotation: multi-select with type
  • Scalar types (bool, int, float, str, Literal, Enum): single value
  • Other types (dataclass, BaseModel): use directly
The response_title and response_description arguments customize the label and description of the wrapped value property for the scalar/dict/list shorthand forms. They are only valid when FastMCP is wrapping the response type; passing them with a full BaseModel/dataclass raises TypeError, because in those cases the user already controls field metadata via Field(title=..., description=...).

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handle_elicit_accept

Handle an accepted elicitation response. Args:
  • config: The elicitation configuration from parse_elicit_response_type
  • content: The response content from the client
Returns:
  • AcceptedElicitation with the extracted/validated data

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get_elicitation_schema

Get the schema for an elicitation response. Args:
  • response_type: The type of the response

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validate_elicitation_json_schema

Validate that a JSON schema follows MCP elicitation requirements. This ensures the schema is compatible with MCP elicitation requirements:
  • Must be an object schema
  • Must only contain primitive field types (string, number, integer, boolean)
  • Must be flat (no nested objects or arrays of objects)
  • Allows const fields (for Literal types) and enum fields (for Enum types)
  • Only primitive types and their nullable variants are allowed
Args:
  • schema: The JSON schema to validate
Raises:
  • TypeError: If the schema doesn’t meet MCP elicitation requirements

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Classes

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ElicitationJsonSchema

Custom JSON schema generator for MCP elicitation that always inlines enums. MCP elicitation requires inline enum schemas without ref/ref/defs references. This generator ensures enums are always generated inline for compatibility. Optionally adds enumNames for better UI display when available. Methods:

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generate_inner

Override to prevent ref generation for enums and handle list schemas.

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list_schema

Generate schema for list types, detecting enum items for multi-select.

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enum_schema

Generate inline enum schema. Always generates enum pattern: {"enum": [value, ...]} Titled enums are handled separately via dict-based syntax in ctx.elicit().

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AcceptedElicitation

Result when user accepts the elicitation.

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ScalarElicitationType

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ElicitConfig

Configuration for an elicitation request. Attributes:
  • schema: The JSON schema to send to the client
  • response_type: The type to validate responses with (None for raw schemas)
  • is_raw: True if schema was built directly (extract “value” from response)