CUA MCP Server

An agentic Model Context Protocol (MCP) server for CUA Cloud - delegate desktop automation tasks to an autonomous vision-based agent. Images never leave the server; only text summaries are returned.

Production URL: https://cua-mcp-server.vercel.app/mcp

What is CUA?

CUA (Computer Use Agent) provides cloud-based virtual machine sandboxes that AI agents can control. This MCP server exposes CUA's capabilities through a clean task-delegation API:

• Create and manage VMs (Linux, Windows, macOS)
• Delegate tasks - "Open Chrome and navigate to google.com"
• Get text summaries - No images in your context window
• Query screen state - Vision-based descriptions without taking action

Architecture

Claude Code (Orchestrator)
    │
    │ run_task("Open Chrome and go to google.com")
    ▼
┌─────────────────────────────────────────────────────────────┐
│  CUA MCP Server (Agentic)                                   │
│  ┌───────────────────────────────────────────────────────┐  │
│  │  Internal Agent Loop                                  │  │
│  │  1. screenshot() → CUA sandbox                        │  │
│  │  2. screenshot → Claude API (computer_use tool)       │  │
│  │  3. Claude returns: click(x,y) / type("text") / done  │  │
│  │  4. Execute action on sandbox                         │  │
│  │  5. Loop until complete                               │  │
│  └───────────────────────────────────────────────────────┘  │
└─────────────────────────────────────────────────────────────┘
    │
    ▼
{ success: true, summary: "Opened Chrome...", steps_taken: 5 }
(TEXT ONLY - no images)

Project Structure

api/mcp.ts                     # MCP protocol handler
lib/
├── agent/                     # Modular agent architecture
│   ├── index.ts               # Public exports
│   ├── types.ts               # Type definitions
│   ├── config.ts              # Model configurations
│   ├── execute.ts             # Main agent loop
│   ├── describe.ts            # Screen description
│   ├── progress.ts            # Progress tracking
│   └── actions/               # Action handler registry (16 handlers)
├── cua-client.ts              # CUA Cloud API client
└── tool-schemas.ts            # MCP tool definitions

Available Tools (9 total)

Sandbox Management (5 tools)

Tool	Description
list_sandboxes	List all CUA cloud sandboxes with their current status
get_sandbox	Get details of a specific sandbox including API URLs
start_sandbox	Start a stopped sandbox
stop_sandbox	Stop a running sandbox
restart_sandbox	Restart a sandbox

Note: Create and delete sandboxes via the CUA Dashboard - the Cloud API doesn't expose these operations.

Agentic Tools (4 tools)

Tool	Description
describe_screen	Get a text description of current screen state using vision AI. No actions taken.
run_task	Execute a computer task autonomously. Returns immediately with task_id for polling.
get_task_progress	Poll progress of running tasks. Returns current step, last action, and reasoning.
get_task_history	Retrieve results of a previously executed task by ID.

Quick Start

1. Get a CUA API Key

1. Go to cua.ai/signin
2. Navigate to Dashboard > API Keys > New API Key
3. Copy your API key (starts with sk_cua-api01_...)

2. Configure Claude Code

Add to your ~/.claude.json:

{
  "mcpServers": {
    "cua": {
      "command": "npx",
      "args": ["-y", "mcp-remote", "https://cua-mcp-server.vercel.app/mcp"]
    }
  }
}

3. Use with Claude Code

You: "List my CUA sandboxes"
Claude: [Uses list_sandboxes tool]

You: "Start my-sandbox"
Claude: [Uses start_sandbox tool]

You: "Open Firefox and go to google.com on my-sandbox"
Claude: [Uses run_task with task="Open Firefox and navigate to google.com"]
→ Returns: { success: true, summary: "Opened Firefox, navigated to google.com", steps_taken: 4 }

You: "What's currently on the screen?"
Claude: [Uses describe_screen tool]
→ Returns: { description: "Firefox browser showing Google homepage with search box..." }

Usage Examples

Automate a Web Task

You: "On my-sandbox, open Chrome, go to github.com, and search for 'mcp server'"

Claude uses run_task:
- task: "Open Chrome browser, navigate to github.com, find the search box, type 'mcp server' and press Enter"
- Returns summary of what happened (no screenshots in your context)

Check Screen State

You: "What's on the screen right now?"

Claude uses describe_screen:
- focus: "ui" (or "text" or "full")
- Returns text description of UI elements, buttons, text content

Ask Specific Questions

You: "Is there a login button visible?"

Claude uses describe_screen:
- question: "Is there a login button visible?"
- Returns: "Yes, there is a blue 'Sign In' button in the top right corner..."

Self-Hosting

Prerequisites

• Vercel account with Pro plan (for 800s function timeout)
• Vercel Blob storage
• Anthropic API key

Deploy Your Own Instance

# Clone the repository
git clone https://github.com/anthropics/cua-mcp-server.git
cd cua-mcp-server

# Install dependencies
npm install

# Deploy to Vercel
vercel --prod

Environment Variables

Variable	Description	Required
CUA_API_KEY	Your CUA Cloud API key	Yes
ANTHROPIC_API_KEY	Anthropic API key for vision processing	Yes
BLOB_READ_WRITE_TOKEN	Vercel Blob token (auto-added)	Yes
CUA_API_BASE	Custom API base URL (default: https://api.cua.ai)	No
CUA_MODEL	Model to use: claude-opus-4-5 (default) or claude-sonnet-4-5	No

Setting Up Vercel Blob

1. Go to your Vercel project dashboard
2. Navigate to Storage → Create → Blob
3. The BLOB_READ_WRITE_TOKEN will be automatically added

Pass API Key Per-Request

If you don't want to store the CUA API key on the server:

{
  "mcpServers": {
    "cua": {
      "command": "npx",
      "args": [
        "-y", "mcp-remote",
        "https://your-deployment.vercel.app/mcp",
        "--header", "X-CUA-API-Key: sk_cua-api01_your-key-here"
      ]
    }
  }
}

API Reference

MCP Endpoint

URL: POST /mcp

Content-Type: application/json

Example: Run Task

{
  "jsonrpc": "2.0",
  "method": "tools/call",
  "id": 1,
  "params": {
    "name": "run_task",
    "arguments": {
      "sandbox_name": "s-linux-abc123",
      "task": "Open Firefox and navigate to google.com",
      "max_steps": 30,
      "timeout_seconds": 120
    }
  }
}

Response:

{
  "jsonrpc": "2.0",
  "id": 1,
  "result": {
    "content": [{
      "type": "text",
      "text": "{\"task_id\":\"task_123...\",\"success\":true,\"summary\":\"Opened Firefox, navigated to google.com\",\"steps_taken\":4,\"duration_ms\":8500}"
    }]
  }
}

Example: Describe Screen

{
  "jsonrpc": "2.0",
  "method": "tools/call",
  "id": 2,
  "params": {
    "name": "describe_screen",
    "arguments": {
      "sandbox_name": "s-linux-abc123",
      "focus": "ui",
      "question": "Is there a search box visible?"
    }
  }
}

Model Support

Model	Env Variable	Tool Version	Features
Claude Opus 4.5 (default)	CUA_MODEL=claude-opus-4-5	computer_20251124	Zoom support, higher accuracy
Claude Sonnet 4.5	CUA_MODEL=claude-sonnet-4-5	computer_20250124	Faster, lower cost

Supported Computer Actions

The agent can perform the following actions autonomously:

UI Actions:

• screenshot - Capture current screen
• left_click, right_click, double_click, triple_click, middle_click - Mouse clicks at coordinates
• mouse_move - Move cursor to coordinates
• left_click_drag - Click and drag from start to end coordinates
• left_mouse_down, left_mouse_up - Press/release mouse button
• scroll - Scroll up/down/left/right
• wait - Pause execution
• zoom - View specific screen region at full resolution (Opus 4.5 only, defaults to center if no coordinate)

Keyboard:

• type - Type text
• key - Press key or key combination (e.g., "ctrl+c")
• hold_key - Hold a modifier key down (auto-releases after next action)

Constraints

Constraint	Value
Function timeout	800 seconds (Vercel Pro)
Max steps per task	100
Default steps	100
Default timeout	750 seconds
Task history TTL	24 hours
Display resolution	Dynamic (default 1024x768)

Sandbox Types

OS	Size	CPU	RAM	Use Case
Linux	small	2	4GB	Development, testing
Linux	medium	4	8GB	Build tasks, CI/CD
Linux	large	8	16GB	Heavy workloads
Windows	small	2	4GB	Basic Windows apps
Windows	medium	4	8GB	Office, development
Windows	large	8	16GB	Enterprise apps
macOS	small	2	4GB	iOS development
macOS	medium	4	8GB	Xcode builds
macOS	large	8	16GB	Heavy compilation

Regions

• north-america - US East (lowest latency for US users)
• europe - EU West
• asia - Asia Pacific

Troubleshooting

"CUA API key required"

Set CUA_API_KEY environment variable in Vercel or pass via X-CUA-API-Key header.

"ANTHROPIC_API_KEY not configured"

The server needs an Anthropic API key for vision processing. Add it to your Vercel environment variables.

Task times out

• Default timeout is 750 seconds
• Reduce task complexity or break into smaller steps
• Check if sandbox is responsive with describe_screen

Task exceeds max steps

• Default is 100 steps (max 100)
• Break complex tasks into smaller subtasks
• Use more specific task descriptions

Resources

• CUA Documentation
• CUA Cloud Dashboard
• Anthropic Computer Use
• MCP Protocol Specification

License

MIT