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

# Tool Policy Overview

> Control which tools an MCP session can access using allowlist, denylist, or unrestricted modes.

Tool Policy lets you restrict which tools an MCP session can call. It is stored as an optional `toolPolicy` field on the `Session` object and persisted in SQL storage backends (Neon, Supabase) when provided.

## How It Works

Each session can carry a `toolPolicy` with one of three modes:

| Mode        | Behavior                                              |
| ----------- | ----------------------------------------------------- |
| `all`       | All tools are allowed (default when no policy is set) |
| `allowlist` | Only the listed tool IDs are allowed                  |
| `denylist`  | All tools are allowed **except** the listed tool IDs  |

A tool ID is a composite string: `{serverId}::{toolName}` (e.g. `my-server::get_weather`).

## When to Use

* **Multi-tenant deployments** — restrict each session to a subset of tools
* **Security boundaries** — prevent a session from calling privileged tools
* **Gradual rollouts** — allowlist tools as they are vetted per session

## Session Data Structure

The `toolPolicy` field is optional on `Session`:

```typescript theme={null}
interface Session {
  sessionId: string;
  userId: string;
  // ... other fields
  toolPolicy?: ToolPolicy;
}

interface ToolPolicy {
  mode: 'all' | 'allowlist' | 'denylist';
  toolIds: string[];
  updatedAt: number;
}
```

When no policy is provided (`undefined`), the SDK treats it as `all` — all tools are permitted.