> ## Documentation Index
> Fetch the complete documentation index at: https://fastmcp-ts.docs.prefect.io/llms.txt
> Use this file to discover all available pages before exploring further.

# ToolAnnotations

Defined in: [server/FastMCP.ts:274](https://github.com/PrefectHQ/fastmcp-ts/blob/main/src/server/FastMCP.ts#L274)

Behavioral hints for a tool (MCP 2025-03-26). Advisory only — clients may use
them for UI/UX and safety decisions (e.g. auto-approving a read-only call); the
server does not enforce them. Per the MCP spec, annotations from an untrusted
server should not be relied upon.

## Properties

### destructiveHint?

```ts theme={null}
optional destructiveHint?: boolean;
```

Defined in: [server/FastMCP.ts:280](https://github.com/PrefectHQ/fastmcp-ts/blob/main/src/server/FastMCP.ts#L280)

The tool may perform destructive updates. Only meaningful when readOnlyHint is false. Default: true.

***

### idempotentHint?

```ts theme={null}
optional idempotentHint?: boolean;
```

Defined in: [server/FastMCP.ts:282](https://github.com/PrefectHQ/fastmcp-ts/blob/main/src/server/FastMCP.ts#L282)

Repeated calls with the same arguments have no additional effect. Only meaningful when readOnlyHint is false. Default: false.

***

### openWorldHint?

```ts theme={null}
optional openWorldHint?: boolean;
```

Defined in: [server/FastMCP.ts:284](https://github.com/PrefectHQ/fastmcp-ts/blob/main/src/server/FastMCP.ts#L284)

The tool may interact with an open world of external entities. Default: true.

***

### readOnlyHint?

```ts theme={null}
optional readOnlyHint?: boolean;
```

Defined in: [server/FastMCP.ts:278](https://github.com/PrefectHQ/fastmcp-ts/blob/main/src/server/FastMCP.ts#L278)

The tool does not modify its environment. Default: false.

***

### title?

```ts theme={null}
optional title?: string;
```

Defined in: [server/FastMCP.ts:276](https://github.com/PrefectHQ/fastmcp-ts/blob/main/src/server/FastMCP.ts#L276)

Human-readable title for display.