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fastmcp.utilities.types

Common types used across FastMCP.

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Functions

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get_fn_name 

get_fn_name(fn: Callable[..., Any]) -> str

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get_cached_typeadapter 

get_cached_typeadapter(cls: T) -> TypeAdapter[T]
TypeAdapters are heavy objects, and in an application context we’d typically create them once in a global scope and reuse them as often as possible. However, this isn’t feasible for user-generated functions. Instead, we use a cache to minimize the cost of creating them as much as possible.

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issubclass_safe 

issubclass_safe(cls: type, base: type) -> bool
Check if cls is a subclass of base, even if cls is a type variable.

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is_class_member_of_type 

is_class_member_of_type(cls: Any, base: type) -> bool
Check if cls is a member of base, even if cls is a type variable. Base can be a type, a UnionType, or an Annotated type. Generic types are not considered members (e.g. T is not a member of list[T]).

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find_kwarg_by_type 

find_kwarg_by_type(fn: Callable, kwarg_type: type) -> str | None
Find the name of the kwarg that is of type kwarg_type. Includes union types that contain the kwarg_type, as well as Annotated types.

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create_function_without_params 

create_function_without_params(fn: Callable[..., Any], exclude_params: list[str]) -> Callable[..., Any]
Create a new function with the same code but without the specified parameters in annotations. This is used to exclude parameters from type adapter processing when they can’t be serialized. The excluded parameters are removed from the function’s annotations dictionary.

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replace_type 

replace_type(type_, type_map: dict[type, type])
Given a (possibly generic, nested, or otherwise complex) type, replaces all instances of old_type with new_type. This is useful for transforming types when creating tools. Args:
  • type_: The type to replace instances of old_type with new_type.
  • old_type: The type to replace.
  • new_type: The type to replace old_type with.
Examples: 
>>> replace_type(list[int | bool], {int: str})
list[str | bool]

>>> replace_type(list[list[int]], {int: str})
list[list[str]]

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Classes

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FastMCPBaseModel

Base model for FastMCP models.

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Image

Helper class for returning images from tools. Methods:

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to_image_content 

to_image_content(self, mime_type: str | None = None, annotations: Annotations | None = None) -> mcp.types.ImageContent
Convert to MCP ImageContent.

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to_data_uri 

to_data_uri(self, mime_type: str | None = None) -> str
Get image as a data URI.

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Audio

Helper class for returning audio from tools. Methods:

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to_audio_content 

to_audio_content(self, mime_type: str | None = None, annotations: Annotations | None = None) -> mcp.types.AudioContent

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File

Helper class for returning file data from tools. Methods:

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to_resource_content 

to_resource_content(self, mime_type: str | None = None, annotations: Annotations | None = None) -> mcp.types.EmbeddedResource

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ContextSamplingFallbackProtocol