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

# LangChain

> Use @sigilcore/agent-hooks with LangChain to wrap tools with Sigil policy enforcement.

## Installation

```bash theme={null}
npm install @sigilcore/agent-hooks
```

## Usage

```typescript theme={null}
import { wrapLangChainTool } from '@sigilcore/agent-hooks';

HTTP note: typed `http` requires an explicit valid method in the tool input. Inputs without a method remain legacy `web_fetch`; no default method is inferred.

const config = {
  apiKey: process.env.SIGIL_API_KEY!,
  agentId: 'my-langchain-agent',
};

// Wrap any LangChain tool:
const safeTool = wrapLangChainTool(myTool, config);

// safeTool.call() now checks Sigil policy before executing
// If denied, returns a JSON rejection string the agent can parse
```

## How It Works

`wrapLangChainTool` wraps the tool's `call()` method. When the agent invokes the tool, Sigil evaluates the intent against your `warranty.md` policy first. On approval, the original `call()` executes. On denial or hold, a typed JSON rejection is returned as the tool output.

```typescript theme={null}
// The wrapped tool behaves identically to the original
// Except every call() is gated by Sigil policy first
const result = await safeTool.call('rm -rf /tmp/important');
// result = '{"sigil_decision":"DENIED","sigil_error_code":"SIGIL_POLICY_VIOLATION_BLOCKED_COMMAND"...}'
```

The JSON rejection is returned as the tool output string — LangChain agents receive it as a tool result and adjust their reasoning accordingly.

## Configuration

| Field       | Type       | Required | Default                      | Description                    |
| ----------- | ---------- | -------- | ---------------------------- | ------------------------------ |
| `apiKey`    | `string`   | Yes      | —                            | Sigil API key (`sk_sigil_...`) |
| `apiUrl`    | `string`   | No       | `https://sign.sigilcore.com` | Sigil Sign endpoint            |
| `agentId`   | `string`   | No       | `'agent'`                    | Agent identifier               |
| `onDenied`  | `function` | No       | —                            | Called when action is denied   |
| `onPending` | `function` | No       | —                            | Called when action is held     |
| `onError`   | `function` | No       | —                            | Called on network error        |