Where can I find the proper way to send data between the client and the server? my ping pong method is telling me 'invalid message' every time

[murrlincoln]

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Question Category

• Protocol Specification
• SDK Usage
• Server Implementation
• General Implementation
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Your Question

I'm having some issues getting any data to be passed from Claude Desktop client to my MCP server. I'm trying to do this basic ping pong, and even when the client seems like its sending a parameter it's not being registered. My server only has 7 tools, and I have no idea what the issue could be.

const pingPong = server.tool(
    'pingPong',
    {
      description: 'Handles ping-pong protocol',
      inputSchema: {
        type: "object",
        required: ["message"],
        properties: {
          message: {
            type: "string",
            pattern: "^ping$"
          }
        }
      }
    },
    async (params) => {
      // Deep debug
      console.error('[DEBUG] pingPong tool invoked');
      console.error('[DEBUG] params:', JSON.stringify(params));
      console.error('[DEBUG] typeof params:', typeof params);
      if (params && typeof params === 'object') {
        console.error('[DEBUG] params keys:', Object.keys(params));
        for (const [k, v] of Object.entries(params)) {
          console.error(`[DEBUG] param key: ${k}, value:`, v, 'typeof:', typeof v);
        }
      }
      // Try both possible locations
      const msg = params?.message ?? params?.arguments?.message;
      console.error('[DEBUG] msg:', msg);
      console.error('[DEBUG] params.message:', params?.message);
      console.error('[DEBUG] params.arguments?.message:', params?.arguments?.message);
      return {
        content: [{
          type: "text",
          text: msg === "ping" ? "pong" : "Invalid message"
        }]
      };
    }
  );```

[olaservo]

What SDK version are you using?

[murrlincoln]

^1.11.1

[murrlincoln]

I'm also trying by adding that ping pong function into the Brave Search server to no avail on v1.0.1 . There, the client to server interaction happens for the web search tool but not for my ping pong tool. I just get Invalid message

[murrlincoln]

Here are the client error logs:

2025-05-10T03:09:30.114Z [info] [brave-search] Message from client: {"method":"prompts/list","params":{},"jsonrpc":"2.0","id":8}
2025-05-10T03:09:30.114Z [info] [X402ShopMCPServer] Message from client: {"method":"prompts/list","params":{},"jsonrpc":"2.0","id":4}
2025-05-10T03:09:30.114Z [info] [brave-search] Message from server: {"jsonrpc":"2.0","id":8,"error":{"code":-32601,"message":"Method not found"}}
2025-05-10T03:09:30.114Z [info] [X402ShopMCPServer] Message from server: {"jsonrpc":"2.0","id":4,"error":{"code":-32601,"message":"Method not found"}}
2025-05-10T03:09:40.227Z [info] [brave-search] Message from client: {"method":"tools/call","params":{"name":"pingPong","arguments":{"query":"ping"}},"jsonrpc":"2.0","id":9}
2025-05-10T03:09:40.230Z [info] [brave-search] Message from server: {"jsonrpc":"2.0","id":9,"result":{"content":[{"type":"text","text":"Invalid message"}],"isError":true}}

[murrlincoln]

Resolved -- went through the example quickstart and that worked.

[olaservo]

Glad to hear to resolved this. One difference with the quickstart server example is that it uses Zod schemas for tool params (vs plain JSON schemas like your original example) which for me tends to play nicer as well.