# Source: https://gofastmcp.com/python-sdk/fastmcp-utilities-types.md

> ## Documentation Index
> Fetch the complete documentation index at: https://gofastmcp.com/llms.txt
> Use this file to discover all available pages before exploring further.

# types

# `fastmcp.utilities.types`

Common types used across FastMCP.

## Functions

### `get_fn_name` <sup><a href="https://github.com/jlowin/fastmcp/blob/main/src/fastmcp/utilities/types.py#L34" target="_blank"><Icon icon="github" style="width: 14px; height: 14px;" /></a></sup>

```python  theme={"theme":{"light":"snazzy-light","dark":"dark-plus"}}
get_fn_name(fn: Callable[..., Any]) -> str
```

### `get_cached_typeadapter` <sup><a href="https://github.com/jlowin/fastmcp/blob/main/src/fastmcp/utilities/types.py#L45" target="_blank"><Icon icon="github" style="width: 14px; height: 14px;" /></a></sup>

```python  theme={"theme":{"light":"snazzy-light","dark":"dark-plus"}}
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#L120" target="_blank"><Icon icon="github" style="width: 14px; height: 14px;" /></a></sup>

```python  theme={"theme":{"light":"snazzy-light","dark":"dark-plus"}}
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#L130" target="_blank"><Icon icon="github" style="width: 14px; height: 14px;" /></a></sup>

```python  theme={"theme":{"light":"snazzy-light","dark":"dark-plus"}}
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` <sup><a href="https://github.com/jlowin/fastmcp/blob/main/src/fastmcp/utilities/types.py#L152" target="_blank"><Icon icon="github" style="width: 14px; height: 14px;" /></a></sup>

```python  theme={"theme":{"light":"snazzy-light","dark":"dark-plus"}}
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.

### `create_function_without_params` <sup><a href="https://github.com/jlowin/fastmcp/blob/main/src/fastmcp/utilities/types.py#L178" target="_blank"><Icon icon="github" style="width: 14px; height: 14px;" /></a></sup>

```python  theme={"theme":{"light":"snazzy-light","dark":"dark-plus"}}
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.

### `replace_type` <sup><a href="https://github.com/jlowin/fastmcp/blob/main/src/fastmcp/utilities/types.py#L451" target="_blank"><Icon icon="github" style="width: 14px; height: 14px;" /></a></sup>

```python  theme={"theme":{"light":"snazzy-light","dark":"dark-plus"}}
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  theme={"theme":{"light":"snazzy-light","dark":"dark-plus"}}
>>> 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#L38" 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#L235" 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#L286" target="_blank"><Icon icon="github" style="width: 14px; height: 14px;" /></a></sup>

```python  theme={"theme":{"light":"snazzy-light","dark":"dark-plus"}}
to_image_content(self, mime_type: str | None = None, annotations: Annotations | None = None) -> mcp.types.ImageContent
```

Convert to MCP ImageContent.

#### `to_data_uri` <sup><a href="https://github.com/jlowin/fastmcp/blob/main/src/fastmcp/utilities/types.py#L301" target="_blank"><Icon icon="github" style="width: 14px; height: 14px;" /></a></sup>

```python  theme={"theme":{"light":"snazzy-light","dark":"dark-plus"}}
to_data_uri(self, mime_type: str | None = None) -> str
```

Get image as a data URI.

### `Audio` <sup><a href="https://github.com/jlowin/fastmcp/blob/main/src/fastmcp/utilities/types.py#L307" 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#L344" target="_blank"><Icon icon="github" style="width: 14px; height: 14px;" /></a></sup>

```python  theme={"theme":{"light":"snazzy-light","dark":"dark-plus"}}
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#L365" target="_blank"><Icon icon="github" style="width: 14px; height: 14px;" /></a></sup>

Helper class for returning file data from tools.

**Methods:**

#### `to_resource_content` <sup><a href="https://github.com/jlowin/fastmcp/blob/main/src/fastmcp/utilities/types.py#L404" target="_blank"><Icon icon="github" style="width: 14px; height: 14px;" /></a></sup>

```python  theme={"theme":{"light":"snazzy-light","dark":"dark-plus"}}
to_resource_content(self, mime_type: str | None = None, annotations: Annotations | None = None) -> mcp.types.EmbeddedResource
```

### `ContextSamplingFallbackProtocol` <sup><a href="https://github.com/jlowin/fastmcp/blob/main/src/fastmcp/utilities/types.py#L488" target="_blank"><Icon icon="github" style="width: 14px; height: 14px;" /></a></sup>