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

# Overview

> Production ready JavaScript AST validation with extensible rules and presets for safe code execution

ast-guard is a production-ready AST validation library for JavaScript. It inspects user-provided or LLM-generated code before execution, blocking dangerous constructs and enforcing API usage policies. ast-guard powers Enclave's first security layer and can be used standalone for any JavaScript validation needs.

<CardGroup cols={3}>
  <Card title="16 Built-in Rules" icon="shield">
    Block eval, dangerous globals, prototype manipulation, unbounded loops, ReDoS, and more with battle-tested validation rules.
  </Card>

  <Card title="Pre-Scanner Defense" icon="radar">
    Layer 0 security that runs BEFORE parsing - catches DoS attacks that could crash the parser itself.
  </Card>

  <Card title="AgentScript Preset" icon="robot">
    Purpose-built preset for LLM-generated orchestration code with whitelist-only globals and strict control flow.
  </Card>
</CardGroup>

## When to Use ast-guard

* **LLM-generated code** - Validate AI-written JavaScript before execution
* **User scripts** - Accept arbitrary JavaScript with deterministic guardrails
* **Workflow builders** - Enforce API usage and block dangerous constructs
* **Compliance requirements** - Audit trails showing exactly which rule blocked a script

<Note>
  ast-guard is a pure TypeScript package with zero native dependencies. It works in Node.js 22+ and can be used standalone or as part of the Enclave execution environment.
</Note>

## Installation

```bash theme={"theme":{"light":"snazzy-light","dark":"dark-plus"}}
npm install @enclave-vm/ast
```

## Quick Start

```ts theme={"theme":{"light":"snazzy-light","dark":"dark-plus"}}
import { JSAstValidator, createAgentScriptPreset } from '@enclave-vm/ast';

// Create validator with AgentScript preset (recommended for LLM code)
const validator = new JSAstValidator(createAgentScriptPreset());

// Validate code
const result = await validator.validate(`
  const users = await callTool('users:list', { limit: 10 });
  return users.filter(u => u.active);
`);

if (result.valid) {
  console.log('Code is safe to execute');
} else {
  console.log('Blocked:', result.issues);
}
```

<Tip>
  Instantiate `JSAstValidator` once and reuse it. This keeps presets, custom rules, and caches consistent across requests.
</Tip>

## Validation Result

```ts theme={"theme":{"light":"snazzy-light","dark":"dark-plus"}}
interface ValidationResult {
  valid: boolean;
  issues: ValidationIssue[];
}

interface ValidationIssue {
  rule: string;        // Rule that triggered
  message: string;     // Human-readable message
  severity: 'error' | 'warning';
  location?: {
    line: number;
    column: number;
  };
}
```

## Validation Options

```ts theme={"theme":{"light":"snazzy-light","dark":"dark-plus"}}
const result = await validator.validate(source, {
  maxIssues: 10,           // Cap findings returned
  stopOnFirstError: true,  // Halt on first error (faster)
});

// Get stats for monitoring
const stats = validator.getStats(result, durationMs);
```

<Warning>
  AST Guard prevents unsafe syntax from entering your sandbox, but it does not execute or sandbox code itself. Pair it with enclave-vm for complete defense-in-depth.
</Warning>

## Related

* [Pre-Scanner](/enclave/core-libraries/ast-guard/pre-scanner) - Layer 0 defense before parsing
* [AgentScript Preset](/enclave/core-libraries/ast-guard/agentscript-preset) - Preset for LLM code
* [Security Rules](/enclave/core-libraries/ast-guard/security-rules) - Built-in rules reference
* [enclave-vm](/enclave/core-libraries/enclave-vm/overview) - Runtime sandbox