fastmcp/docs/python-sdk/fastmcp-utilities-types.mdx
2025-06-25 09:43:22 -05:00

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---
title: types
sidebarTitle: types
---
# `fastmcp.utilities.types`
Common types used across FastMCP.
## Functions
### `get_cached_typeadapter` <sup><a href="https://github.com/jlowin/fastmcp/blob/main/src/fastmcp/utilities/types.py#L35"><Icon icon="github" size="14" /></a></sup>
```python
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.
### `issubclass_safe` <sup><a href="https://github.com/jlowin/fastmcp/blob/main/src/fastmcp/utilities/types.py#L45"><Icon icon="github" size="14" /></a></sup>
```python
issubclass_safe(cls: type, base: type) -> bool
```
Check if cls is a subclass of base, even if cls is a type variable.
### `is_class_member_of_type` <sup><a href="https://github.com/jlowin/fastmcp/blob/main/src/fastmcp/utilities/types.py#L55"><Icon icon="github" size="14" /></a></sup>
```python
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]).
### `find_kwarg_by_type` <sup><a href="https://github.com/jlowin/fastmcp/blob/main/src/fastmcp/utilities/types.py#L77"><Icon icon="github" size="14" /></a></sup>
```python
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.
## Classes
### `FastMCPBaseModel` <sup><a href="https://github.com/jlowin/fastmcp/blob/main/src/fastmcp/utilities/types.py#L28"><Icon icon="github" size="14" /></a></sup>
Base model for FastMCP models.
### `Image` <sup><a href="https://github.com/jlowin/fastmcp/blob/main/src/fastmcp/utilities/types.py#L94"><Icon icon="github" size="14" /></a></sup>
Helper class for returning images from tools.
**Methods:**
#### `to_image_content` <sup><a href="https://github.com/jlowin/fastmcp/blob/main/src/fastmcp/utilities/types.py#L131"><Icon icon="github" size="14" /></a></sup>
```python
to_image_content(self, mime_type: str | None = None, annotations: Annotations | None = None) -> ImageContent
```
Convert to MCP ImageContent.
### `Audio` <sup><a href="https://github.com/jlowin/fastmcp/blob/main/src/fastmcp/utilities/types.py#L153"><Icon icon="github" size="14" /></a></sup>
Helper class for returning audio from tools.
**Methods:**
#### `to_audio_content` <sup><a href="https://github.com/jlowin/fastmcp/blob/main/src/fastmcp/utilities/types.py#L190"><Icon icon="github" size="14" /></a></sup>
```python
to_audio_content(self, mime_type: str | None = None, annotations: Annotations | None = None) -> AudioContent
```
### `File` <sup><a href="https://github.com/jlowin/fastmcp/blob/main/src/fastmcp/utilities/types.py#L211"><Icon icon="github" size="14" /></a></sup>
Helper class for returning audio from tools.
**Methods:**
#### `to_resource_content` <sup><a href="https://github.com/jlowin/fastmcp/blob/main/src/fastmcp/utilities/types.py#L250"><Icon icon="github" size="14" /></a></sup>
```python
to_resource_content(self, mime_type: str | None = None, annotations: Annotations | None = None) -> EmbeddedResource
```