---
title: types
sidebarTitle: types
---
# `fastmcp.utilities.types`
Common types used across FastMCP.
## Functions
### `get_fn_name`
```python
get_fn_name(fn: Callable[..., Any]) -> str
```
### `get_cached_typeadapter`
```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`
```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`
```python
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]).
### `find_kwarg_by_type`
```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`
```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:
```python
>>> replace_type(list[int | bool], {int: str})
list[str | bool]
>>> replace_type(list[list[int]], {int: str})
list[list[str]]
```
## Classes
### `FastMCPBaseModel`
Base model for FastMCP models.
### `Image`
Helper class for returning images from tools.
**Methods:**
#### `to_image_content`
```python
to_image_content(self, mime_type: str | None = None, annotations: Annotations | None = None) -> mcp.types.ImageContent
```
Convert to MCP ImageContent.
### `Audio`
Helper class for returning audio from tools.
**Methods:**
#### `to_audio_content`
```python
to_audio_content(self, mime_type: str | None = None, annotations: Annotations | None = None) -> mcp.types.AudioContent
```
### `File`
Helper class for returning file data from tools.
**Methods:**
#### `to_resource_content`
```python
to_resource_content(self, mime_type: str | None = None, annotations: Annotations | None = None) -> mcp.types.EmbeddedResource
```
### `ContextSamplingFallbackProtocol`