elicitation

fastmcp.server.elicitation

Functions

parse_elicit_response_type

parse_elicit_response_type(response_type: Any) -> ElicitConfig

Parse response_type into schema and handling configuration.

Supports multiple syntaxes:

• None: Empty object schema, expect empty response
• 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

handle_elicit_accept

handle_elicit_accept(config: ElicitConfig, content: Any) -> AcceptedElicitation[Any]

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

get_elicitation_schema

get_elicitation_schema(response_type: type[T]) -> dict[str, Any]

Get the schema for an elicitation response.

Args:

• response_type: The type of the response

validate_elicitation_json_schema

validate_elicitation_json_schema(schema: dict[str, Any]) -> None

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

Classes

ElicitationJsonSchema

Custom JSON schema generator for MCP elicitation that always inlines enums.

MCP elicitation requires inline enum schemas without $ref/$defs references. This generator ensures enums are always generated inline for compatibility. Optionally adds enumNames for better UI display when available.

Methods:

generate_inner

generate_inner(self, schema: core_schema.CoreSchema) -> JsonSchemaValue

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

list_schema

list_schema(self, schema: core_schema.ListSchema) -> JsonSchemaValue

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

enum_schema

enum_schema(self, schema: core_schema.EnumSchema) -> JsonSchemaValue

Generate inline enum schema.

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

AcceptedElicitation

Result when user accepts the elicitation.

ScalarElicitationType

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)