MCP Builder

---
name: mcp-builder
description: |
  Trigger when the user wants to build an MCP server, create MCP tools,
  or extend AI capabilities with custom integrations. Phrases: "build MCP",
  "create MCP server", "custom tools", "MCP integration".
allowed-tools:
  - Bash(command *)
  - Read
  - Write
  - Edit
  - Glob
  - Grep
---

# MCP Builder

Build Model Context Protocol servers from scratch with tools, resources,
and transport configuration.

## Prerequisites

- Node.js 18+ or Python 3.10+
- `npm install @modelcontextprotocol/sdk` (TypeScript)
- or `pip install mcp` (Python)

## Steps

1. **Decide on tools and resources.** List what your MCP server will expose:
   - Tools: actions the AI can take (e.g., run query, send message)
   - Resources: data the AI can read (e.g., database schema, config files)

2. **Scaffold the server (TypeScript):**
   ```typescript
   import { McpServer } from "@modelcontextprotocol/sdk/server/mcp.js";
   import { StdioServerTransport } from "@modelcontextprotocol/sdk/server/stdio.js";

   const server = new McpServer({
     name: "my-server",
     version: "1.0.0",
   });

   server.tool("my_tool", "Description of what it does", {
     param: { type: "string", description: "What this param is" },
   }, async ({ param }) => {
     // Implementation
     return { content: [{ type: "text", text: "Result" }] };
   });

   const transport = new StdioServerTransport();
   await server.connect(transport);
   ```

3. **Add to MCP config:**
   ```json
   {
     "mcpServers": {
       "my-server": {
         "command": "node",
         "args": ["path/to/server.js"]
       }
     }
   }
   ```

4. **Test the server:**
   - Run it manually and send test requests
   - Verify tool schemas are correct
   - Check error handling for invalid inputs

5. **Best practices:**
   - Always validate inputs with schemas
   - Return structured errors, not raw exceptions
   - Keep tools focused - one action per tool
   - Use descriptive names and descriptions (the AI reads them)