Custom Tool Builder
An MCP server that allows users to dynamically add custom tools/functions at runtime
What is Custom Tool Builder?
Custom Tool Builder is a Model Context Protocol (MCP) server that allows AI assistants like Claude, Cursor, and VS Code to mcp server that allows users to dynamically add custom tools/functions at runtime
An MCP server that allows users to dynamically add custom tools/functions at runtime
This server falls under the Developer Tools category on MCPgee, the world's largest MCP server directory with 33,000+ servers.
Features
- An MCP server that allows users to dynamically add custom to
Use Cases
Maintainer
Works with
Installation
Manual Installation
npx diy-toolsConfiguration
Configuration Details
claude_desktop_config.json
Performance
Response Metrics
Resource Usage
How to Set Up and Use Custom Tool Builder
DIY Tools MCP Server is a dynamic tool-building platform that lets you register, remove, and invoke custom functions at runtime without restarting the MCP server. It supports writing tools in Python, JavaScript, TypeScript, Bash, and Ruby, then calling them directly from Claude or any MCP-compatible client. This is ideal for developers who want to extend Claude's capabilities with bespoke scripts, automation helpers, or domain-specific utilities on the fly.
Prerequisites
- Node.js 18+ and npm installed
- TypeScript 5.0+ (installed via npm)
- Runtime for the languages you'll use in tools: Python 3.x, Bash, or Ruby as needed
- An MCP-compatible client such as Claude Desktop or Claude Code
Clone and install the repository
Clone the diy-tools-mcp repository and install all Node.js dependencies.
git clone https://github.com/hesreallyhim/diy-tools-mcp.git
cd diy-tools-mcp
npm installBuild the TypeScript source
Compile the TypeScript source files into JavaScript so the server can be run.
npm run buildStart the MCP server
Start the server in production mode, or use the dev mode for automatic reloading during development.
# Production
npm start
# Development with auto-reload
npm run devConfigure your MCP client
Add the server to your claude_desktop_config.json (Claude Desktop) or .mcp.json (Claude Code) so the client can connect via stdio.
{
"mcpServers": {
"diy-tools": {
"command": "node",
"args": ["/absolute/path/to/diy-tools-mcp/dist/index.js"]
}
}
}Register your first custom tool
Use the built-in add_tool capability to register a custom function. Functions are stored as JSON files in the functions/ directory and validated for syntax automatically.
Manage and inspect registered tools
Use list_tools to see all available custom tools, view_source to inspect their source code, and remove_tool to deregister tools you no longer need — all without restarting the server.
Custom Tool Builder Examples
Client configuration
Add to claude_desktop_config.json to connect Claude Desktop to the DIY Tools server.
{
"mcpServers": {
"diy-tools": {
"command": "node",
"args": ["/Users/yourname/diy-tools-mcp/dist/index.js"]
}
}
}Prompts to try
Example prompts once the server is connected to Claude.
- "Add a new tool called 'timestamp' that returns the current UTC time as an ISO string — write it in Python"
- "List all the custom tools you have available"
- "Show me the source code of the 'timestamp' tool"
- "Remove the 'timestamp' tool from the registry"
- "Create a Bash tool called 'disk_usage' that runs df -h and returns the output"Troubleshooting Custom Tool Builder
Tool registration fails with a syntax error
The server validates function syntax before registration. Review the error message, fix the code in your function definition, and try registering again. Ensure the function uses the correct entry point (default: main) or specify a custom entry point in the registration payload.
Python tools fail because packages are missing
Automatic dependency installation is not yet implemented. Manually install required Python packages with 'pip install <package>' in the same Python environment that the server uses before registering the tool.
Server not found after configuring the MCP client
Ensure you used the absolute path to the compiled dist/index.js file in the config. Run 'npm run build' first to generate the dist/ directory, then restart the MCP client.
Frequently Asked Questions about Custom Tool Builder
What is Custom Tool Builder?
Custom Tool Builder is a Model Context Protocol (MCP) server that mcp server that allows users to dynamically add custom tools/functions at runtime It connects AI assistants to external tools and data sources through a standardized interface.
How do I install Custom Tool Builder?
Follow the installation instructions on the Custom Tool Builder GitHub repository. Clone the repo, install dependencies, and add the server config to your AI client.
Which AI clients work with Custom Tool Builder?
Custom Tool Builder works with all major MCP-compatible AI clients including Claude Desktop, Claude Code, Cursor, VS Code (GitHub Copilot), Windsurf, and Cline.
Is Custom Tool Builder free to use?
Yes, Custom Tool Builder is open source and available under the MIT license. You can use it freely in both personal and commercial projects.
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Set Up Custom Tool Builder in Your Editor
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Quick Config Preview
Add this to your claude_desktop_config.json or .cursor/mcp.json
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