fastmcp/docs/python-sdk/fastmcp-utilities-types.mdx
2025-07-18 10:19:16 -05:00

137 lines
4.6 KiB
Text

---
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#L31" target="_blank"><Icon icon="github" style="width: 14px; height: 14px;" /></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#L41" target="_blank"><Icon icon="github" style="width: 14px; height: 14px;" /></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#L51" target="_blank"><Icon icon="github" style="width: 14px; height: 14px;" /></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#L73" target="_blank"><Icon icon="github" style="width: 14px; height: 14px;" /></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.
### `replace_type` <sup><a href="https://github.com/jlowin/fastmcp/blob/main/src/fastmcp/utilities/types.py#L293" target="_blank"><Icon icon="github" style="width: 14px; height: 14px;" /></a></sup>
```python
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]]
## Classes
### `FastMCPBaseModel` <sup><a href="https://github.com/jlowin/fastmcp/blob/main/src/fastmcp/utilities/types.py#L24" target="_blank"><Icon icon="github" style="width: 14px; height: 14px;" /></a></sup>
Base model for FastMCP models.
### `Image` <sup><a href="https://github.com/jlowin/fastmcp/blob/main/src/fastmcp/utilities/types.py#L90" target="_blank"><Icon icon="github" style="width: 14px; height: 14px;" /></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#L127" target="_blank"><Icon icon="github" style="width: 14px; height: 14px;" /></a></sup>
```python
to_image_content(self, mime_type: str | None = None, annotations: Annotations | None = None) -> mcp.types.ImageContent
```
Convert to MCP ImageContent.
### `Audio` <sup><a href="https://github.com/jlowin/fastmcp/blob/main/src/fastmcp/utilities/types.py#L149" target="_blank"><Icon icon="github" style="width: 14px; height: 14px;" /></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#L186" target="_blank"><Icon icon="github" style="width: 14px; height: 14px;" /></a></sup>
```python
to_audio_content(self, mime_type: str | None = None, annotations: Annotations | None = None) -> mcp.types.AudioContent
```
### `File` <sup><a href="https://github.com/jlowin/fastmcp/blob/main/src/fastmcp/utilities/types.py#L207" target="_blank"><Icon icon="github" style="width: 14px; height: 14px;" /></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#L246" target="_blank"><Icon icon="github" style="width: 14px; height: 14px;" /></a></sup>
```python
to_resource_content(self, mime_type: str | None = None, annotations: Annotations | None = None) -> mcp.types.EmbeddedResource
```