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

{
  "mcpServers": {
    "filesystem": {
      "command": "npx",
      "args": ["-y", "@modelcontextprotocol/server-filesystem", "/path/to/allowed/dir"]
    },
    "github": {
      "command": "npx",
      "args": ["-y", "@modelcontextprotocol/server-github"],
      "env": {
        "GITHUB_PERSONAL_ACCESS_TOKEN": "ghp_xxxx"
      }
    }
  }
}

{
  "filesystem": {
    "command": "npx",
    "args": ["-y", "@modelcontextprotocol/server-filesystem", "/Users/me/projects"]
  }
}

{
  "github": {
    "command": "npx",
    "args": ["-y", "@modelcontextprotocol/server-github"],
    "env": {
      "GITHUB_PERSONAL_ACCESS_TOKEN": "ghp_xxxx"
    }
  }
}

{
  "postgres": {
    "command": "npx",
    "args": ["-y", "@modelcontextprotocol/server-postgres", "postgresql://user:pass@localhost/db"]
  }
}

{
  "sqlite": {
    "command": "npx",
    "args": ["-y", "@modelcontextprotocol/server-sqlite", "--db-path", "/path/to/db.sqlite"]
  }
}

{
  "brave-search": {
    "command": "npx",
    "args": ["-y", "@modelcontextprotocol/server-brave-search"],
    "env": {
      "BRAVE_API_KEY": "your-api-key"
    }
  }
}

{
  "slack": {
    "command": "npx",
    "args": ["-y", "@modelcontextprotocol/server-slack"],
    "env": {
      "SLACK_BOT_TOKEN": "xoxb-xxxx",
      "SLACK_TEAM_ID": "T12345"
    }
  }
}

#!/usr/bin/env python3
from mcp.server import Server
from mcp.types import Tool, TextContent

server = Server("my-server")

@server.list_tools()
async def list_tools():
    return [
        Tool(
            name="my_tool",
            description="Does something useful",
            inputSchema={
                "type": "object",
                "properties": {
                    "query": {"type": "string", "description": "Input query"}
                },
                "required": ["query"]
            }
        )
    ]

@server.call_tool()
async def call_tool(name: str, arguments: dict):
    if name == "my_tool":
        result = process(arguments["query"])
        return [TextContent(type="text", text=result)]

if __name__ == "__main__":
    import asyncio
    asyncio.run(server.run())

{
  "my-custom-server": {
    "command": "python",
    "args": ["/path/to/my_server.py"]
  }
}

npm init -y
npm install @modelcontextprotocol/sdk

import { Server } from "@modelcontextprotocol/sdk/server/index.js";
import { StdioServerTransport } from "@modelcontextprotocol/sdk/server/stdio.js";

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

server.setRequestHandler("tools/list", async () => ({
  tools: [{
    name: "my_tool",
    description: "Does something",
    inputSchema: {
      type: "object",
      properties: { query: { type: "string" } },
      required: ["query"]
    }
  }]
}));

server.setRequestHandler("tools/call", async (request) => {
  if (request.params.name === "my_tool") {
    return { content: [{ type: "text", text: "Result" }] };
  }
});

new StdioServerTransport().connect(server);

# Run server directly
npx -y @modelcontextprotocol/server-filesystem /tmp

# Check logs (Claude Desktop)
tail -f ~/Library/Logs/Claude/mcp*.log