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MCP Server Tester

by r-huijts

Development/TestingServer TestingClaude AITesting ToolConfiguration

MCP Server Tester is a configuration-driven testing tool for Model Context Protocol (MCP) servers. It provides a comprehensive solution for validating, benchmarking, and ensuring reliability of MCP servers that integrate with AI models like Claude.

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MCP Server Tester

⚠️ WORK IN PROGRESS: This project is under active development and has not been thoroughly tested yet. Features may be incomplete, contain bugs, or change significantly. Use at your own risk in non-production environments only.

A powerful, configuration-driven testing tool for Model Context Protocol (MCP) servers. This project provides a comprehensive solution for validating, benchmarking, and ensuring reliability of MCP servers that integrate with AI models like Claude.

Current Status

This tool is in early development stage with:

  • ✅ Basic configuration framework implemented
  • ✅ MCP server connection capabilities
  • ✅ Test generation using Claude AI
  • ✅ Natural language query generation for tests
  • ✅ Report generation in multiple formats
  • 🚧 Comprehensive test validation (in progress)
  • 🚧 Additional reporting options (in progress)
  • ❌ Full test coverage of the tool itself
  • ❌ Production hardening

If you're interested in contributing, please feel free to open issues and submit pull requests.

Introduction

The Model Context Protocol (MCP) enables AI models to access external tools and data sources through standardized interfaces. As MCP servers grow in complexity and importance, ensuring their correct functionality becomes critical. The MCP Server Tester addresses this need by:

  • Automating tests for all tools exposed by an MCP server
  • Leveraging Claude AI to generate intelligent, contextually-relevant test cases
  • Validating responses against expected outcomes and schemas
  • Providing detailed reports to identify issues and performance bottlenecks

This tool is designed for MCP server developers, AI integration teams, and quality assurance professionals who need to ensure their MCP implementations are robust, reliable, and correctly follow the protocol specifications.

Repository

Features

  • 🔍 Automatically discovers available tools from any MCP server
  • 🧪 Generates realistic test cases for each tool using Claude AI
  • ⚡ Executes tests and validates responses
  • 📊 Provides detailed test reports
  • 🔑 Supports multiple connection methods through configuration
  • Configuration-Based: Simple JSON configuration for defining MCP servers to test
  • Multiple Server Support: Test multiple MCP servers at once
  • Comprehensive Testing: Tests all tools exposed by each server
  • Natural Language Context: Includes the user query that would trigger each tool, providing real-world context
  • Detailed Reports: Generate reports in console, JSON, or HTML formats
  • Secure: Keeps API keys in environment variables, not in configuration files

Prerequisites

  • Node.js 18 or higher
  • An Anthropic API key for generating test cases

Installation

Since this project is still in development, installation is done by cloning the repository:

# Clone the repository
git clone https://github.com/r-huijts/mcp-server-tester.git
cd mcp-server-tester

# Install dependencies
npm install

# Build the project
npm run build

# Create a symbolic link to use it globally (optional)
npm link

Configuration-Based Usage

The MCP Server Tester is designed to be driven entirely through configuration files. This approach offers several advantages:

  • Reusability: Define your servers once, test them repeatedly
  • Version control: Check in your test configurations alongside your code
  • Sharing: Easily share server test configurations with team members

Basic Usage

# Create a .env file with your Anthropic API key
echo "ANTHROPIC_API_KEY=your-api-key-here" > .env

# Run tests using the configuration
mcp-server-tester

# Use a custom configuration file
mcp-server-tester path/to/my-config.json

Configuration File Structure

The configuration file (mcp-servers.json) controls all aspects of testing:

{
  "numTestsPerTool": 3,
  "timeoutMs": 10000,
  "outputFormat": "console",
  "outputPath": "./reports/results.json",
  "verbose": false,
  "mcpServers": {
    "filesystem": {
      "command": "npx",
      "args": ["-y", "@modelcontextprotocol/server-filesystem", "./"],
      "env": {
        "DEBUG": "true"
      }
    },
    "github": {
      "command": "npx",
      "args": ["-y", "@modelcontextprotocol/server-github"],
      "env": {
        "GITHUB_PERSONAL_ACCESS_TOKEN": "your-github-token-here"
      }
    },
    "dev-server": {
      "command": "node",
      "args": ["/absolute/path/to/your/dev-server.js"],
      "env": {
        "DEBUG": "true",
        "NODE_ENV": "development"
      }
    }
  }
}

By default, the tool will test all servers defined in the mcpServers section. If you want to test only specific servers, you can add an optional servers array:

{
  "servers": ["filesystem", "dev-server"],
  "numTestsPerTool": 3,
  // other settings...
  "mcpServers": {
    // server definitions...
  }
}

Configuration Options

Test Settings

| Option | Description | Default | |--------|-------------|---------| | servers | Optional array of specific server names to test | All servers in mcpServers | | numTestsPerTool | Number of tests to generate per tool | 3 | | timeoutMs | Timeout for test execution in milliseconds | 10000 | | outputFormat | Format for test reports (json, console, html) | "console" | | outputPath | Path to output file | undefined | | verbose | Enable verbose logging | false |

Server Definitions

The mcpServers section defines all available servers that can be tested:

| Property | Description | Required | |----------|-------------|----------| | command | Executable or command to run | Yes | | args | Array of command-line arguments | Yes | | env | Environment variables to set | Yes |

Server Connection Types

You can define various types of MCP servers in your configuration:

NPM Package
"npm-package": {
  "command": "npx",
  "args": ["-y", "@modelcontextprotocol/server-github"],
  "env": {}
}
Local Script with Relative Path
"python-script": {
  "command": "python",
  "args": ["./servers/custom_server.py"],
  "env": {
    "PORT": "8080"
  }
}
Local Script with Absolute Path

Useful for testing development versions of servers:

"dev-server": {
  "command": "node",
  "args": ["/absolute/path/to/your/dev-server.js"],
  "env": {
    "DEBUG": "true",
    "NODE_ENV": "development"
  }
}
Socket Connection
"remote-socket": {
  "command": "nc",
  "args": ["localhost", "3000"],
  "env": {}
}

API Key Management

For security reasons, your Anthropic API key should only be set in one of these ways:

  1. Environment variable: ANTHROPIC_API_KEY=your-api-key
  2. .env file in your project directory: 
    ANTHROPIC_API_KEY=your-api-key

Important: Never put your API key in the configuration file, as it may be committed to version control.

Command-Line Options

MCP Server Tester supports minimal command-line options:

| Option | Description | |--------|-------------| | --init or -i | Create a default configuration file | | --list or -l | List all servers defined in your configuration | | --help or -h | Display help information | | [config-path] | Specify a custom configuration file path |

Test Generation Process

The tool uses Claude AI to automatically generate appropriate test cases for each tool exposed by the MCP server:

  1. It discovers all available tools from the server
  2. For each tool, it analyzes:
    • Tool name and description
    • Required and optional parameters
    • Parameter types and constraints
  3. Claude generates multiple test cases per tool:
    • Happy path tests with valid inputs
    • Edge case tests with boundary values
    • Error case tests with invalid inputs

Each test case includes:

  • Description of what's being tested
  • Input parameters
  • Expected outcome criteria

Test Execution and Validation

For each server specified in the configuration (or all servers if none specified):

  1. The tool connects to the server
  2. It discovers all available tools
  3. It generates test cases for each tool
  4. It executes each test case against the server
  5. It validates the responses against expected outcomes
  6. It generates a report of the results

Reporting Options

The tool can generate reports in multiple formats, controlled by the outputFormat configuration option:

Console Output (Default)

Displays test results directly in the terminal.

JSON Report

Creates a structured JSON file at the path specified in outputPath.

HTML Report

Generates an HTML report with visualizations at the path specified in outputPath.

Complete Examples

Basic Setup and Testing

  1. Create a default configuration file:

    mcp-server-tester --init

  2. Edit the mcp-servers.json file to add your own servers and settings

  3. Create a .env file with your Anthropic API key:

    echo "ANTHROPIC_API_KEY=your-api-key-here" > .env

  4. Run the tests:

    mcp-server-tester

Testing a Dev Version of Your Server

To test a development version of your MCP server:

  1. Add a configuration for your development server with the absolute path:
{
  "mcpServers": {
    "my-dev-server": {
      "command": "node",
      "args": ["/path/to/your/project/dist/server.js"],
      "env": {
        "DEBUG": "true",
        "NODE_ENV": "development"
      }
    }
  }
}
  1. Run the tests:
mcp-server-tester

Testing Multiple Different Configurations

You can maintain different configuration files for different testing scenarios:

# Create different config files for different environments
cp mcp-servers.json config-dev.json
cp mcp-servers.json config-prod.json

# Edit each file with appropriate settings

# Run tests with specific config
mcp-server-tester ./config-dev.json
mcp-server-tester ./config-prod.json

Troubleshooting

Connection Issues

If you're having trouble connecting to an MCP server:

  1. Verify the server configuration in your mcp-servers.json file
  2. Check if the server supports the MCP protocol
  3. Try increasing the timeoutMs for slower servers
  4. Enable verbose logging by setting verbose: true
  5. Check server process startup with environment variable DEBUG=true

API Key Issues

If you encounter API key issues:

  1. Verify your Anthropic API key is valid
  2. Make sure the API key is correctly set in your environment or .env file
  3. Check for any spaces or extra characters in your API key
  4. Confirm that the .env file is in the correct location (project root)

Tool Execution Failures

If tool executions are failing:

  1. Ensure your server implements the MCP protocol correctly
  2. Check the server logs for errors
  3. Verify the tool parameters are valid
  4. Increase the timeout if the tool takes longer to execute

Node.js Deprecation Warnings

punycode Module Deprecation Warning

If you encounter this warning:

(node:71439) [DEP0040] DeprecationWarning: The `punycode` module is deprecated. Please use a userland alternative instead.

This is a harmless warning from Node.js about an internal module being deprecated. It doesn't affect the functionality of the MCP Server Tester. The warning comes from one of the dependencies and will be resolved in future updates.

Solutions:

  1. Ignore the warning - It doesn't affect functionality
  2. Suppress warnings - Run with the NODE_NO_WARNINGS=1 environment variable: 
    NODE_NO_WARNINGS=1 mcp-server-tester
  3. Use the npm scripts - The included npm scripts already suppress these warnings: 
    npm start

Development

To set up the development environment:

# Clone the repository
git clone https://github.com/r-huijts/mcp-server-tester.git
cd mcp-server-tester

# Install dependencies
npm install

# Create your .env file
cp .env.example .env
# Edit .env and add your API key

# Run the tool in development mode
npm run dev

License

MIT