🧪 Vitest MCP Server

MCP Vitest runner with LLM-optimized test output, log capturing, and line-by-line coverage analysis.

Table of Contents

• 😢 The Problem with LLMs and Testing
• ✨ Key Features
• 🚀 Quick Start
• 📋 Requirements
• 🧰 Tools
• 🔄 Multi-Repository Support
• 🪝 Claude Code Hook
• 🤖 LLM instructions
• ⚙️ Configuration
• 🔍 Development Mode & Debugging
• 🔧 Troubleshooting
• 📜 License

😢 The Problem with LLMs and Testing 😢

• Noisy test output - Raw Vitest output can be extremely verbose eating up tokens/context with useless information.
• Full test suite runs - LLMs sometimes forget to limit the scope of the test run, causing full test suite runs to be executed.
• Buried console logs - Console logs can be hidden in test output, making it inefficient for LLMs to debug test failures.
• Raw coverage files - Raw coverage files are too large for AI to parse.
• Watch mode - LLMs get stuck when vitest runs in watch mode.

✨ Key Features ✨

• Smart Test Results with adaptive, structured output to limit noise.
• Console Log Capture to prevent logs from getting lost in test output.
• Coverage Analysis with line-by-line gap insights.
• Multi-Repository Support in a single session with context switching.
• Safety Guards prevent full project runs, watch mode, invalid vitest commands, and context hogging.

🚀 Quick Start 🚀

The Vitest MCP server can be used with any MCP-compatible IDE or tool and works with all Javascript or Typescript Vitests. The basic configuration is:

{
  "mcpServers": {
    "vitest": {
      "command": "npx",
      "args": ["-y", "@djankies/vitest-mcp"]
    }
  }
}

⚠️ Note: The above example may not be valid for all MCP clients. Verify your client's specific setup instructions.

🛠️ Client-Specific Setup

Select your preferred IDE or tool from the setup guides below:

Configuration Methods

Claude Code supports multiple configuration approaches:

Method 1: CLI Wizard (Interactive)

# Add server with interactive prompts
claude mcp add vitest -- npx -y @djankies/vitest-mcp

# Add to project scope (shareable with team)
claude mcp add --scope project vitest -- npx -y @djankies/vitest-mcp

Method 2: Direct Configuration File

Create or edit .mcp.json in your project root:

{
  "mcpServers": {
    "vitest": {
      "type": "stdio",
      "command": "npx",
      "args": ["-y", "@djankies/vitest-mcp"],
      "env": {}
    }
  }
}

Configuration Scopes

• Local (default): Personal, project-specific - stored in user settings
• Project: Team-shared - stored in .mcp.json in project root
• User: Available across all projects - global configuration

Setup Steps

1. Navigate to your project directory
2. Choose either CLI or file-based configuration
3. For CLI: Run claude mcp add vitest npx -y @djankies/vitest-mcp
4. For file: Create .mcp.json with the configuration above
5. Verify with /mcp command in Claude Code to see connection status

Usage

Once configured, use the MCP server naturally in your conversations:

• "Set the project root to this directory"
• "Run the auth component tests"
• "Show me the test coverage gaps"

Configuration Location

• macOS: ~/Library/Application Support/Claude/claude_desktop_config.json
• Windows: %APPDATA%\Claude\claude_desktop_config.json

Example Configuration

{
  "mcpServers": {
    "vitest": {
      "command": "npx",
      "args": ["-y", "@djankies/vitest-mcp"]
    }
  }
}

Setup Steps

1. Open Claude Desktop
2. Navigate to File → Settings → Developer
3. Click Edit Config
4. Add the configuration above
5. Save and restart Claude Desktop
6. Look for the MCP indicator (🔌) in the conversation input

Configuration Methods

• Workspace: .vscode/mcp.json in your project
• Global: Run command MCP: Open User Configuration

Example Configuration

{
  "mcpServers": {
    "vitest": {
      "command": "npx",
      "args": ["-y", "@djankies/vitest-mcp"],
      "type": "stdio"
    }
  }
}

Setup Steps

1. Install VS Code 1.86+ with GitHub Copilot
2. Open Command Palette (Cmd/Ctrl + Shift + P)
3. Run MCP: Add Server
4. Select Workspace Settings or Global
5. Add the configuration and save
6. Access via Copilot Chat: Add Context → MCP Resources

Configuration Location

• Project: .cursor/mcp.json in your project directory
• Global: ~/.cursor/mcp.json for all workspaces

Example Configuration

{
  "mcpServers": {
    "vitest": {
      "command": "npx",
      "args": ["-y", "@djankies/vitest-mcp"]
    }
  }
}

Setup Steps

1. Create the configuration file in your preferred location
2. Add the server configuration
3. Restart Cursor
4. The MCP server will be available in Cursor's AI chat
5. Use natural language to run tests: "Run the auth component tests"

Configuration Location

Similar to Cursor, but use serverUrl instead of url for remote servers

Example Configuration

{
  "mcpServers": {
    "vitest": {
      "command": "npx",
      "args": ["-y", "@djankies/vitest-mcp"]
    }
  }
}

Setup Steps

1. Open Windsurf Settings (Cmd/Ctrl + ,)
2. Navigate to Cascade settings
3. Add MCP server configuration
4. Reload MCP servers to activate

Configuration via Cline UI

Example Configuration

{
  "mcpServers": {
    "vitest": {
      "command": "npx",
      "args": ["-y", "@djankies/vitest-mcp"]
    }
  }
}

Setup Steps

1. Open VS Code with Cline extension installed
2. Click the Cline icon in the sidebar
3. Click MCP Servers → Configure MCP Servers
4. Add the vitest-mcp configuration
5. Save and reload VS Code
6. Access through Cline's chat interface

3. Use It 🎮

Once configured, you can use natural language to interact with your tests:

• "Run the tests for this component"
• "Debug this test file"
• "Analyze the coverage for this file"

Or prepend your message with vitest-mcp: to ensure the tools are used:

• "vitest-mcp: run tests for this component"
• "vitest-mcp: debug this test file"
• "vitest-mcp: analyze coverage for this file"

📋 Requirements

• Node.js: 18+ 🟢
• Vitest: 0.34.0+ 🧪
• Coverage: @vitest/coverage-v8 (for coverage analysis) 📊

npm install --save-dev vitest@latest @vitest/coverage-v8@latest

🧰 Tools

set_project_root

🚨 Required first - Set the project root for all operations.

| Parameter | Type | Required | Description | |-----------|------|----------|-------------| | path | string | Yes | Project root path |

list_tests

List test files in your project. Helps keep LLMs from slipping back to using command line tools while working with tests.

| Parameter | Type | Required | Description | |-----------|------|----------|-------------| | directory | string | Yes | Directory to search for test files |

run_tests

Execute tests with structured output.

Parameters:

| Parameter | Type | Required | Description | |-----------|------|----------|-------------| | target | string | Yes | File or directory to test | | format | string | No | Output format: "summary" or "detailed" (auto-detects based on results) | | showLogs | boolean | No | Include console output with [stdout] or [stderr] prefixes | | project | string | No | Vitest project name for monorepos |

analyze_coverage

Analyze test coverage with gap insights.

| Parameter | Type | Required | Description | |-----------|------|----------|-------------| | target | string | Yes | File or directory to analyze coverage for | | format | string | No | Output format: "summary" (overview only) or "detailed" (includes line-by-line coverage) | | exclude | string[] | No | Patterns to exclude from coverage (e.g., ["**/.stories."]) |

Note: Coverage thresholds should be configured in your vitest.config.ts file, not via MCP parameters.

Automatically excludes test utilities, mocks, stories, and e2e files.

🔄 Multi-Repository Support

// Project A
set_project_root({ path: "/path/to/frontend" })
run_tests({ target: "./src" })

// Project B
set_project_root({ path: "/path/to/backend" })
run_tests({ target: "./src" })

🪝 Claude Code Hook

Automatically redirect Vitest commands to MCP tools:

# Run from project root
curl -o .claude/vitest-hook.sh https://raw.githubusercontent.com/djankies/vitest-mcp/refs/heads/main/.claude/vitest-hook.sh
chmod +x .claude/vitest-hook.sh

Then add to your project's .claude/settings.local.json:

{
  "hooks": {
    "PreToolUse": [{
      "matcher": "Bash",
      "hooks": [{ "type": "command", "command": ".claude/vitest-hook.sh" }]
    }]
  }
}

The hook can be bypassed with the BYPASS_VITEST_HOOK environment variable:

BYPASS_VITEST_HOOK=1 npm test

Or export for entire session:

export BYPASS_VITEST_HOOK=1

🤖 LLM instructions

Encourage claude or your ide to use the tools correctly: CLAUDE.example.md

⚙️ Configuration

Vitest Configuration Priority

The MCP server automatically detects and uses Vitest configuration files in the following priority order:

1. vitest.mcp.config.ts - MCP-specific configuration (highest priority) 🔝
2. vitest.config.ts
3. vitest.config.js
4. vitest.config.mjs
5. vite.config.ts (if it contains test configuration)
6. vite.config.js (if it contains test configuration)
7. vite.config.mjs (if it contains test configuration)

This allows you to have a dedicated MCP-specific configuration that won't interfere with your regular development workflow:

// vitest.mcp.config.ts
import { defineConfig } from 'vitest/config';

export default defineConfig({
  test: {
    // MCP-specific settings
    reporters: ['json'],
    coverage: {
      enabled: true,
      provider: 'v8',
      reporter: ['json', 'html'],
    },
  },
});

Coverage Thresholds

To enable coverage threshold reporting in the analyze_coverage tool, just configure in your Vitest configuration file:

// vitest.config.ts or vitest.mcp.config.ts
import { defineConfig } from 'vitest/config';

export default defineConfig({
  test: {
    coverage: {
      provider: 'v8',
      reporter: ['text', 'json', 'html'],
      thresholds: {
        lines: 90,
        functions: 85,
        branches: 80,
        statements: 90
      }
    }
  }
});

💡 Note: Coverage analysis is always available regardless of threshold settings. Threshold reporting just helps keep your LLM on target.

Vitest-MCP Configuration File

Optional .vitest-mcp.json in home or project directory:

{
  "safety": {
    "allowedPaths": ["/Users/username/Projects"]
  },
  "testDefaults": {
    "format": "detailed",
    "timeout": 60000
  }
}

Priority Order

Configuration is merged in the following order (highest priority first):

1. Command-line flags
2. Environment variables
3. Configuration file
4. Built-in defaults

🧑🏻‍💻 Development Mode & Debugging

Enable Debug Mode

Set the debug environment variable for detailed logging:

VITEST_MCP_DEBUG=true

Or in your MCP config file:

{
  "mcpServers": {
    "vitest": {
      "command": "npx",
      "args": ["-y", "@djankies/vitest-mcp"],
      "env": {
        "VITEST_MCP_DEBUG": "true"
      }
    }
  }
}

Development Mode

Enable to test the server on its own codebase:

# Set in .env.development, or in your mcp config file 
VITEST_MCP_DEV_MODE=true

🔧 Troubleshooting

"Vitest not found" - Install: npm install --save-dev vitest@latest

"Coverage provider not found" - Install: npm install --save-dev @vitest/coverage-v8@latest 📊

Hook issues - Bypass with: VITEST_HOOK_BYPASS=1 npm test

Found a bug? Submit a bug report, please, and thank you.

📜 License

MIT — See LICENSE.