# LLM Agent Guide: Using Cremote MCP Server for Web Automation

This document provides comprehensive guidance for LLM agents on how to use the **Cremote MCP Server** for intelligent web automation. The MCP server provides a structured, stateful interface that's optimized for AI-driven web testing and automation workflows.

## What is the Cremote MCP Server?

The **Cremote MCP Server** is a Model Context Protocol implementation that wraps cremote's web automation capabilities in a structured API designed specifically for LLMs. Unlike CLI commands, the MCP server provides:

- **Automatic State Management**: Tracks current tab, tab history, and iframe context
- **Intelligent Abstractions**: High-level tools that combine multiple operations
- **Rich Error Context**: Detailed error information for better debugging
- **Automatic Screenshots**: Built-in screenshot capture for documentation
- **Structured Responses**: Consistent, parseable JSON responses

## Prerequisites

Before using the MCP server, ensure the cremote infrastructure is running:

1. **Check if everything is already running:**
   ```bash
   cremote status
   ```

2. **Start Chromium with remote debugging (if needed):**
   ```bash
   chromium --remote-debugging-port=9222 --user-data-dir=/tmp/chromium-debug &
   ```

3. **Start cremote daemon (if needed):**
   ```bash
   cremotedaemon &
   ```

4. **The MCP server should be configured in your MCP client** (e.g., Claude Desktop)

## Available MCP Tools

### 1. `web_navigate` - Smart Navigation

Navigate to URLs with automatic tab management and optional screenshot capture.

**Parameters:**
- `url` (required): URL to navigate to
- `tab` (optional): Specific tab ID (uses current tab if not specified)
- `screenshot` (optional): Take screenshot after navigation (default: false)
- `timeout` (optional): Timeout in seconds (default: 5)

**Example:**
```json
{
  "name": "web_navigate",
  "arguments": {
    "url": "https://example.com/login",
    "screenshot": true,
    "timeout": 10
  }
}
```

**Smart Behavior:**
- Automatically opens a new tab if none exists
- Updates current tab tracking
- Adds tab to history for easy switching

### 2. `web_interact` - Element Interactions

Interact with web elements through a unified interface.

**Parameters:**
- `action` (required): "click", "fill", "submit", or "upload"
- `selector` (required): CSS selector for the target element
- `value` (optional): Value for fill/upload actions
- `tab` (optional): Tab ID (uses current tab if not specified)
- `timeout` (optional): Timeout in seconds (default: 5)

**Examples:**
```json
// Fill a form field
{
  "name": "web_interact",
  "arguments": {
    "action": "fill",
    "selector": "#username",
    "value": "testuser"
  }
}

// Click a button
{
  "name": "web_interact",
  "arguments": {
    "action": "click",
    "selector": "#login-button"
  }
}

// Submit a form
{
  "name": "web_interact",
  "arguments": {
    "action": "submit",
    "selector": "form#login-form"
  }
}

// Upload a file
{
  "name": "web_interact",
  "arguments": {
    "action": "upload",
    "selector": "input[type=file]",
    "value": "/path/to/file.pdf"
  }
}
```

### 3. `web_extract` - Data Extraction

Extract information from web pages through multiple methods.

**Parameters:**
- `type` (required): "source", "element", or "javascript"
- `selector` (optional): CSS selector (required for "element" type)
- `code` (optional): JavaScript code (required for "javascript" type)
- `tab` (optional): Tab ID (uses current tab if not specified)
- `timeout` (optional): Timeout in seconds (default: 5)

**Examples:**
```json
// Get page source
{
  "name": "web_extract",
  "arguments": {
    "type": "source"
  }
}

// Get specific element HTML
{
  "name": "web_extract",
  "arguments": {
    "type": "element",
    "selector": ".error-message"
  }
}

// Execute JavaScript and get result
{
  "name": "web_extract",
  "arguments": {
    "type": "javascript",
    "code": "document.title"
  }
}

// Check form validation
{
  "name": "web_extract",
  "arguments": {
    "type": "javascript",
    "code": "document.getElementById('email').validity.valid"
  }
}
```

### 4. `web_screenshot` - Screenshot Capture

Take screenshots for documentation and debugging.

**Parameters:**
- `output` (required): File path for the screenshot
- `full_page` (optional): Capture full page vs viewport (default: false)
- `tab` (optional): Tab ID (uses current tab if not specified)
- `timeout` (optional): Timeout in seconds (default: 5)

**Examples:**
```json
// Viewport screenshot
{
  "name": "web_screenshot",
  "arguments": {
    "output": "/tmp/login-page.png"
  }
}

// Full page screenshot
{
  "name": "web_screenshot",
  "arguments": {
    "output": "/tmp/full-page.png",
    "full_page": true
  }
}
```

### 5. `web_manage_tabs` - Tab Management

Manage browser tabs with automatic state tracking.

**Parameters:**
- `action` (required): "open", "close", "list", or "switch"
- `tab` (optional): Tab ID (required for "close" and "switch" actions)
- `timeout` (optional): Timeout in seconds (default: 5)

**Examples:**
```json
// Open new tab
{
  "name": "web_manage_tabs",
  "arguments": {
    "action": "open"
  }
}

// List all tabs
{
  "name": "web_manage_tabs",
  "arguments": {
    "action": "list"
  }
}

// Switch to specific tab
{
  "name": "web_manage_tabs",
  "arguments": {
    "action": "switch",
    "tab": "tab-id-123"
  }
}

// Close current tab
{
  "name": "web_manage_tabs",
  "arguments": {
    "action": "close"
  }
}
```

### 6. `web_iframe` - Iframe Context Management

Switch between main page and iframe contexts for testing embedded content.

**Parameters:**
- `action` (required): "enter" or "exit"
- `selector` (optional): Iframe CSS selector (required for "enter" action)
- `tab` (optional): Tab ID (uses current tab if not specified)

**Examples:**
```json
// Enter iframe context
{
  "name": "web_iframe",
  "arguments": {
    "action": "enter",
    "selector": "iframe#payment-form"
  }
}

// Exit iframe context (return to main page)
{
  "name": "web_iframe",
  "arguments": {
    "action": "exit"
  }
}
```

## Response Format

All MCP tools return a consistent response structure:

```json
{
  "success": true,
  "data": "...",                    // Tool-specific response data
  "screenshot": "/tmp/shot.png",    // Screenshot path (if captured)
  "current_tab": "tab-id-123",      // Current active tab
  "tab_history": ["tab-id-123"],    // Tab history stack
  "iframe_mode": false,             // Whether in iframe context
  "error": null,                    // Error message (if failed)
  "metadata": {}                    // Additional context information
}
```

## Common Automation Patterns

### 1. Login Flow Testing

```json
// 1. Navigate to login page with screenshot
{
  "name": "web_navigate",
  "arguments": {
    "url": "https://myapp.com/login",
    "screenshot": true
  }
}

// 2. Fill credentials
{
  "name": "web_interact",
  "arguments": {
    "action": "fill",
    "selector": "#email",
    "value": "user@example.com"
  }
}

{
  "name": "web_interact",
  "arguments": {
    "action": "fill",
    "selector": "#password",
    "value": "password123"
  }
}

// 3. Submit login
{
  "name": "web_interact",
  "arguments": {
    "action": "click",
    "selector": "#login-button"
  }
}

// 4. Verify success
{
  "name": "web_extract",
  "arguments": {
    "type": "javascript",
    "code": "document.querySelector('.welcome-message')?.textContent"
  }
}

// 5. Document result
{
  "name": "web_screenshot",
  "arguments": {
    "output": "/tmp/login-success.png"
  }
}
```

### 2. Form Validation Testing

```json
// 1. Navigate to form
{
  "name": "web_navigate",
  "arguments": {
    "url": "https://myapp.com/register"
  }
}

// 2. Test empty form submission
{
  "name": "web_interact",
  "arguments": {
    "action": "click",
    "selector": "#submit-button"
  }
}

// 3. Check for validation errors
{
  "name": "web_extract",
  "arguments": {
    "type": "element",
    "selector": ".error-message"
  }
}

// 4. Test invalid email
{
  "name": "web_interact",
  "arguments": {
    "action": "fill",
    "selector": "#email",
    "value": "invalid-email"
  }
}

// 5. Verify JavaScript validation
{
  "name": "web_extract",
  "arguments": {
    "type": "javascript",
    "code": "document.getElementById('email').validity.valid"
  }
}
```

### 3. Multi-Tab Workflow

```json
// 1. Open multiple tabs for comparison
{
  "name": "web_manage_tabs",
  "arguments": {
    "action": "open"
  }
}

{
  "name": "web_navigate",
  "arguments": {
    "url": "https://app.com/admin"
  }
}

{
  "name": "web_manage_tabs",
  "arguments": {
    "action": "open"
  }
}

{
  "name": "web_navigate",
  "arguments": {
    "url": "https://app.com/user"
  }
}

// 2. List tabs to see current state
{
  "name": "web_manage_tabs",
  "arguments": {
    "action": "list"
  }
}

// 3. Switch between tabs as needed
{
  "name": "web_manage_tabs",
  "arguments": {
    "action": "switch",
    "tab": "first-tab-id"
  }
}
```

### 4. Iframe Testing (Payment Forms, Widgets)

```json
// 1. Navigate to page with iframe
{
  "name": "web_navigate",
  "arguments": {
    "url": "https://shop.com/checkout"
  }
}

// 2. Enter iframe context
{
  "name": "web_iframe",
  "arguments": {
    "action": "enter",
    "selector": "iframe.payment-frame"
  }
}

// 3. Interact with iframe content
{
  "name": "web_interact",
  "arguments": {
    "action": "fill",
    "selector": "#card-number",
    "value": "4111111111111111"
  }
}

{
  "name": "web_interact",
  "arguments": {
    "action": "fill",
    "selector": "#expiry",
    "value": "12/25"
  }
}

// 4. Exit iframe context
{
  "name": "web_iframe",
  "arguments": {
    "action": "exit"
  }
}

// 5. Continue with main page
{
  "name": "web_interact",
  "arguments": {
    "action": "click",
    "selector": "#complete-order"
  }
}
```

## Best Practices for LLMs

### 1. State Awareness
- The MCP server automatically tracks state, but always check the response for current context
- Use the `current_tab` and `iframe_mode` fields to understand your current position
- The `tab_history` helps you understand available tabs

### 2. Error Handling
- Always check the `success` field in responses
- Use the `error` field for detailed error information
- Take screenshots when errors occur for debugging: `"screenshot": true`

### 3. Timeout Management
- Use longer timeouts for slow-loading pages or complex interactions
- Default 5-second timeouts work for most scenarios
- Increase timeouts for file uploads or heavy JavaScript applications

### 4. Screenshot Strategy
- Take screenshots at key points for documentation
- Use `full_page: true` for comprehensive page captures
- Screenshot before and after critical actions for debugging

### 5. Verification Patterns
- Always verify actions completed successfully
- Use JavaScript extraction to check application state
- Combine element extraction with JavaScript validation

## Debugging Failed Tests

### 1. Capture Current State
```json
// Get page source for analysis
{
  "name": "web_extract",
  "arguments": {
    "type": "source"
  }
}

// Take screenshot to see visual state
{
  "name": "web_screenshot",
  "arguments": {
    "output": "/tmp/debug-state.png",
    "full_page": true
  }
}

// Check JavaScript console errors
{
  "name": "web_extract",
  "arguments": {
    "type": "javascript",
    "code": "console.error.toString()"
  }
}
```

### 2. Element Debugging
```json
// Check if element exists
{
  "name": "web_extract",
  "arguments": {
    "type": "javascript",
    "code": "document.querySelector('#my-element') !== null"
  }
}

// Get element properties
{
  "name": "web_extract",
  "arguments": {
    "type": "javascript",
    "code": "JSON.stringify({visible: document.querySelector('#my-element')?.offsetParent !== null, text: document.querySelector('#my-element')?.textContent})"
  }
}
```

### 3. Network and Loading Issues
```json
// Check if page is still loading
{
  "name": "web_extract",
  "arguments": {
    "type": "javascript",
    "code": "document.readyState"
  }
}

// Check for JavaScript errors
{
  "name": "web_extract",
  "arguments": {
    "type": "javascript",
    "code": "window.onerror ? 'Errors detected' : 'No errors'"
  }
}
```

## Advantages Over CLI Commands

### 1. **Automatic State Management**
- No need to manually track tab IDs
- Automatic current tab resolution
- Persistent iframe context tracking

### 2. **Rich Error Context**
- Detailed error messages with context
- Automatic screenshot capture on failures
- Structured error responses for better debugging

### 3. **Intelligent Abstractions**
- Combined operations in single tools
- Smart parameter defaults and validation
- Automatic resource management

### 4. **Better Performance**
- Direct library integration (no subprocess overhead)
- Persistent connections to cremote daemon
- Efficient state tracking

### 5. **Structured Responses**
- Consistent JSON format for all responses
- Rich metadata for decision making
- Easy parsing and error handling

## Key Differences from CLI Usage

| Aspect | CLI Commands | MCP Server |
|--------|-------------|------------|
| **State Tracking** | Manual tab ID management | Automatic state management |
| **Error Handling** | Text parsing required | Structured error objects |
| **Screenshots** | Manual command execution | Automatic capture options |
| **Performance** | Subprocess overhead | Direct library calls |
| **Response Format** | Text output | Structured JSON |
| **Context Management** | Manual iframe tracking | Automatic context switching |
| **Resource Cleanup** | Manual tab management | Automatic resource tracking |

The Cremote MCP Server transforms web automation from a series of CLI commands into an intelligent, stateful API that's optimized for AI-driven testing and automation workflows.