# React 19 Validator MCP for AI Agents MCP

> React 19 useActionState Validator MCP for AI Agents. This tool checks your JSX snippets to ensure they follow the strict React 19 requirements for the useActionState hook, specifically verifying function references and initial state arguments to prevent runtime errors in Server Actions.

## Overview
- **Category:** development
- **Price:** Free
- **Endpoint:** https://edge.vinkius.com/vk_preview_RgauFaFAEXI23Uf17fbKMXgg7ocgygpiBgv8DqCT/mcp
- **Tags:** react-19, jsx, server-actions, validation, frontend

## Description

Checking React 19 hook implementations manually is a recipe for runtime errors. This MCP looks at your JSX snippets and verifies that useActionState is used correctly, specifically checking that the first argument is a function reference and the second is an initial state. It's designed to catch mistakes in Server Action signatures before they cause crashes in your application. When you use this through Vinkius, it works right alongside your other development tools in any compatible client, making it easy to validate code as you write it.

## Tools

### validate_use_action_state
Checks if a JSX snippet uses the useActionState hook with the correct function and initial state arguments. It helps prevent broken Server Action implementations.

## Prompt Examples

**Prompt:** 
```
Is this JSX snippet valid: `const [state, action] = useActionState(handleSubmit, null);`?
```

**Response:** 
```
Yes, the implementation is valid. The tool identified `handleSubmit` as the action identifier and `null` as the initial state.
```

**Prompt:** 
```
Check this code: `useActionState(async (prev, fd) => { ... }, 0);`
```

**Response:** 
```
The implementation is invalid because it uses an inline arrow function which prevents the extraction of a clear action identifier.
```

**Prompt:** 
```
Validate `useAction: useActionState(myAction);`
```

**Response:** 
```
The implementation is invalid because the second argument (initial state) is missing from the hook call.
```

## Capabilities

### Verify hook signatures
Checks that the first argument is a function and the second is an initial state.

### Catch Server Action errors
Identifies missing arguments that would cause runtime failures in React 19.

### Inspect JSX snippets
Analyzes code fragments to ensure they follow the new hook API requirements.

### Detect invalid patterns
Flags usage of inline arrow functions that prevent proper action identification.

### Validate argument types
Confirms that the provided initial state is present and correctly structured.

## Use Cases

### Broken Server Action implementation
A developer is migrating to React 19 and uses an agent to refactors code. The agent checks a snippet and finds the hook is missing the initial state argument, preventing a crash.

### Validating React 19 hook signatures
You're refactoring a large component library to React 19 and want to ensure all useActionState calls are valid. Your agent runs through your snippets and flags any that don't meet the new signature requirements.

## Benefits

- Stop runtime errors by catching bad useActionState calls early.
- Ensure Server Actions always have the required initial state argument.
- Automate the tedious task of checking hook arguments with validate_use_action_state.
- Keep your React 19 codebase compliant with the latest API requirements.
- Avoid common mistakes like using inline arrow functions that break action identification.

## How It Works

The bottom line is you stop shipping broken React 19 hooks.

1. Connect your preferred AI client to the Vinkius catalog.
2. Provide a JSX snippet containing your useActionState implementation.
3. Get an immediate report confirming if the hook signature is valid.

## Frequently Asked Questions

**How can I use React 19 Validator MCP to check my code?**
You simply provide your JSX snippet to your AI client, and it uses the validator to check if your hook implementation follows the required signature.

**Will React 19 Validator MCP catch errors in my Server Actions?**
Yes, it specifically looks for the correct function reference and initial state arguments needed for Server Actions to work without runtime errors.

**Can I use React 19 Validator MCP with Cursor or Claude?**
Absolutely. Any MCP-compatible client like Cursor, Claude, or Windsurf can use this tool to inspect your React code snippets.

**Does React 19 Validator MCP check for more than just useActionState?**
This specific MCP is focused on validating the implementation of the useActionState hook within your JSX code.

**Can this tool help me migrate to React 19?**
It's a great companion for migrations, as it helps you quickly verify that your new hook usage adheres to the strict new API requirements.

**What does this tool validate?**
It validates that the `useActionState` hook in a JSX snippet follows the React 19 signature, ensuring the action handler is properly identified and an initial state is provided.

**Can I use this for Server Actions?**
Yes, it is specifically designed to ensure that the action handler pattern used in React 19 Server Actions is structurally sound.

**What happens if the JSX snippet is invalid?**
The `validate_use_action_state` tool will return `isValid: false` along with a list of specific validation errors detailing the structural failures.