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fastmcp.utilities.types

Common types used across FastMCP.

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Functions

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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: type, 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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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) -> ImageContent

Convert to MCP ImageContent.

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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) -> AudioContent

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File

Helper class for returning audio from tools.

Methods:

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to_resource_content

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