---
title: exceptions
sidebarTitle: exceptions
---

# `fastmcp.exceptions`


Custom exceptions for FastMCP.

## Classes

### `FastMCPDeprecationWarning` <sup><a href="https://github.com/PrefectHQ/fastmcp/blob/main/fastmcp_slim/fastmcp/exceptions.py#L13" target="_blank"><Icon icon="github" style="width: 14px; height: 14px;" /></a></sup>


Deprecation warning for FastMCP APIs.

Subclass of DeprecationWarning so that standard warning filters
still apply, but FastMCP can selectively enable its own warnings
without affecting other libraries in the process.


### `FastMCPError` <sup><a href="https://github.com/PrefectHQ/fastmcp/blob/main/fastmcp_slim/fastmcp/exceptions.py#L22" target="_blank"><Icon icon="github" style="width: 14px; height: 14px;" /></a></sup>


Base error for FastMCP.


### `ValidationError` <sup><a href="https://github.com/PrefectHQ/fastmcp/blob/main/fastmcp_slim/fastmcp/exceptions.py#L30" target="_blank"><Icon icon="github" style="width: 14px; height: 14px;" /></a></sup>


Error in validating parameters or return values.


### `ResourceError` <sup><a href="https://github.com/PrefectHQ/fastmcp/blob/main/fastmcp_slim/fastmcp/exceptions.py#L34" target="_blank"><Icon icon="github" style="width: 14px; height: 14px;" /></a></sup>


Error in resource operations.


### `ToolError` <sup><a href="https://github.com/PrefectHQ/fastmcp/blob/main/fastmcp_slim/fastmcp/exceptions.py#L38" target="_blank"><Icon icon="github" style="width: 14px; height: 14px;" /></a></sup>


Error in tool operations.


### `PromptError` <sup><a href="https://github.com/PrefectHQ/fastmcp/blob/main/fastmcp_slim/fastmcp/exceptions.py#L42" target="_blank"><Icon icon="github" style="width: 14px; height: 14px;" /></a></sup>


Error in prompt operations.


### `InvalidSignature` <sup><a href="https://github.com/PrefectHQ/fastmcp/blob/main/fastmcp_slim/fastmcp/exceptions.py#L46" target="_blank"><Icon icon="github" style="width: 14px; height: 14px;" /></a></sup>


Invalid signature for use with FastMCP.


### `ClientError` <sup><a href="https://github.com/PrefectHQ/fastmcp/blob/main/fastmcp_slim/fastmcp/exceptions.py#L50" target="_blank"><Icon icon="github" style="width: 14px; height: 14px;" /></a></sup>


Error in client operations.


### `NotFoundError` <sup><a href="https://github.com/PrefectHQ/fastmcp/blob/main/fastmcp_slim/fastmcp/exceptions.py#L54" target="_blank"><Icon icon="github" style="width: 14px; height: 14px;" /></a></sup>


Object not found.


### `DisabledError` <sup><a href="https://github.com/PrefectHQ/fastmcp/blob/main/fastmcp_slim/fastmcp/exceptions.py#L58" target="_blank"><Icon icon="github" style="width: 14px; height: 14px;" /></a></sup>


Object is disabled.


### `AuthorizationError` <sup><a href="https://github.com/PrefectHQ/fastmcp/blob/main/fastmcp_slim/fastmcp/exceptions.py#L62" target="_blank"><Icon icon="github" style="width: 14px; height: 14px;" /></a></sup>


Error when authorization check fails.