MCP server prompt testing with args

index.ts

import express, { Request, Response } from 'express';

const app = express();
app.use(express.json({ limit: '10mb' }));

const PORT = 8000;
const SERVER_NAME = "My Multi-Prompt MCP Server";
const SERVER_VERSION = "1.3.0";
const PROTOCOL_VERSION = "2025-06-18";

// ============================================================
// SINGLE SOURCE OF TRUTH - All prompt info in one place
// ============================================================
interface PromptDefinition {
  name: string;
  description: string;
  arguments: any[];
  handler: (args: Record<string, any>) => string;
}

const PROMPTS: PromptDefinition[] = [
  {
    name: "say-hi",
    description: "A simple prompt that just says hi (no arguments)",
    arguments: [],
    handler: () => "Say hi"
  },
  {
    name: "single-arg",
    description: "A prompt that takes one required name argument",
    arguments: [
      { name: "name", description: "The name to greet", required: true }
    ],
    handler: (args) => `Say hi ${args.name}`
  },
];

// ============================================================
// MCP Endpoint
// ============================================================
app.post('/mcp', (req: Request, res: Response) => {
  const { jsonrpc, id, method, params = {} } = req.body;

  // Handle notifications
  if (!id && method?.startsWith('notifications/')) {
    console.log(`[MCP] Notification: ${method}`);
    return res.status(202).end();
  }

  // === INITIALIZE ===
  if (method === 'initialize') {
    return res.json({
      jsonrpc: "2.0",
      id,
      result: {
        protocolVersion: PROTOCOL_VERSION,
        serverInfo: {
          name: SERVER_NAME,
          title: "My Multi-Prompt MCP Server",
          version: SERVER_VERSION
        },
        capabilities: {
          prompts: { listChanged: false }
        }
      }
    });
  }

  // === PROMPTS/LIST (strip handler functions) ===
  if (method === 'prompts/list') {
    return res.json({
      jsonrpc: "2.0",
      id,
      result: {
        prompts: PROMPTS.map(p => ({
          name: p.name,
          description: p.description,
          arguments: p.arguments
        }))
      }
    });
  }

  // === PROMPTS/GET (Now fully DRY) ===
  if (method === 'prompts/get') {
    const { name, arguments: args = {} } = params;
    const prompt = PROMPTS.find(p => p.name === name);

    if (!prompt) {
      return res.status(404).json({
        jsonrpc: "2.0",
        id,
        error: { code: -32602, message: `Prompt not found: ${name}` }
      });
    }

    // === Validate required arguments ===
    const missingRequired = prompt.arguments
      .filter(arg => arg.required)
      .filter(arg => !args[arg.name] || args[arg.name].toString().trim() === "");

    if (missingRequired.length > 0) {
      return res.status(400).json({
        jsonrpc: "2.0",
        id,
        error: {
          code: -32602,
          message: `Missing required argument(s): ${missingRequired.map(a => a.name).join(", ")}`
        }
      });
    }

    const promptText = prompt.handler(args);

    return res.json({
      jsonrpc: "2.0",
      id,
      result: {
        description: prompt.description,
        messages: [{
          role: "user",
          content: { type: "text", text: promptText }
        }]
      }
    });
  }

  // === PING ===
  if (method === 'ping') {
    return res.json({ jsonrpc: "2.0", id, result: {} });
  }

  console.warn(`[MCP] Unsupported method: ${method}`);
  return res.status(404).json({
    jsonrpc: "2.0",
    id,
    error: { code: -32601, message: `Method not found: ${method}` }
  });
});

// Health check
app.get('/health', (req: Request, res: Response) => {
  res.json({ status: "ok", server: SERVER_NAME, prompts: PROMPTS.length });
});

app.get('/mcp', (req: Request, res: Response) => {
  res.json({ message: "Multi-prompt MCP server is running." });
});

// Start server
app.listen(PORT, '0.0.0.0', () => {
  console.log(`
╔════════════════════════════════════════════════════════════╗
║ 🚀 My Multi-Prompt MCP Server (Fully DRY)                 ║
╠════════════════════════════════════════════════════════════╣
║ Endpoint:  http://localhost:${PORT}/mcp                    ║
║ Prompts:   mcp-say-hi, mcp-single-arg, mcp-args            ║
╚════════════════════════════════════════════════════════════╝
  `);
});