Custom Tools Advanced

import { McpServer } from "@modelcontextprotocol/sdk/server/mcp.js";
import { StdioServerTransport } from "@modelcontextprotocol/sdk/server/stdio.js";
import { z } from "zod";

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

// Define a custom tool
server.tool(
  "query_database",
  "Execute a read-only SQL query against the application database",
  {
    query: z.string().describe("SQL SELECT query to execute"),
    limit: z.number().optional().default(100).describe("Max rows")
  },
  async ({ query, limit }) => {
    // Validate: only allow SELECT queries
    if (!query.trim().toUpperCase().startsWith("SELECT")) {
      return {
        content: [{ type: "text", text: "Error: Only SELECT queries allowed" }]
      };
    }

    // Execute query (use your database library)
    const results = await db.query(`${query} LIMIT ${limit}`);
    return {
      content: [{ type: "text", text: JSON.stringify(results, null, 2) }]
    };
  }
);

// Start the server
const transport = new StdioServerTransport();
await server.connect(transport);

{
  "mcpServers": {
    "my-tools": {
      "command": "npx",
      "args": ["tsx", "./mcp-server/index.ts"],
      "env": {
        "DATABASE_URL": "$DATABASE_URL"
      }
    }
  }
}

server.tool(
  "check_deployment_status",
  "Check the status of a deployment in our CI/CD system",
  {
    environment: z.enum(["staging", "production"]),
    deploy_id: z.string().optional()
  },
  async ({ environment, deploy_id }) => {
    const url = deploy_id
      ? `https://api.deploy.internal/status/${deploy_id}`
      : `https://api.deploy.internal/latest/${environment}`;

    const response = await fetch(url, {
      headers: { "Authorization": `Bearer ${process.env.DEPLOY_TOKEN}` }
    });
    const data = await response.json();

    return {
      content: [{
        type: "text",
        text: `Deployment Status (${environment}):
- Status: ${data.status}
- Version: ${data.version}
- Deployed: ${data.deployed_at}
- Health: ${data.health_check}`
      }]
    };
  }
);