How do I calculate the full length of the tool name , to debug exceeding limit (60, 64)

[ryan65]

Pre-submission Checklist

• I have checked that this question would not be more appropriate as an issue in a specific repository
• I have searched existing discussions and documentation for answers

Question Category

• Protocol Specification
• SDK Usage
• Server Implementation
• General Implementation
• Documentation
• Other

Your Question

Hi
I have built an MCP Server with Stdio transport.
I see that clients have length limits on the full tool name as its registered with the client. For example with Claude Desktop the limit is 64 and with cursor limit is 60.
If the full name exceeds 60 then cursor will display an error for that tool.
"Combined server and tool name length(87) excceds 60 characters)"

The problem is that the full tool name is a combination of the Mcp server Name as configured in the mcp.json file + the tool name.
For example
If the configuration of mcp.json is
{
"mcpServers": {
"My MCP Server": {
"command": "node",
"args": ["C:\Dev_Env\mcp\main.js"],
"env":{
"LOG_LEVEL" : "debug"
}
}
}
}
and the tool name is getFiles

server.registerTool('getFiles', ...

The full name of the tool as registered with the MCP client will be "My MCP Server: getFiles"

Problem: I want to log an error and throw an exception , when I register all my tools , if one of the tools total length exceeds 60 , HOWEVER
I cant find away to know what the MCP Server Name is in my code. My mcp server config file , is configured by a customer so I dont know what property name customer will give the server in advance.

Question: How can I discover this name in my mcp server code. how can I calculate the total length of the full tool name as registered with the client. I want to notify the user in a log that the total has exceeded and request that they reduce the length of the MCP server name in their config.

Thanks

[isheng-eqi]

The problem you have identified is real: the server has no standard way to discover the name the client assigned to it in mcp.json. But there are practical solutions.

Why the server cannot know its own client-configured name

The MCP protocol does not include the server's configuration name in any handshake or initialization message. The initialize request/response exchanges capabilities and server metadata (serverInfo.name), but this is the server's self-reported name (what you set in your code), not the client's configuration key (what the customer types in mcp.json).

// initialize response — THIS is what the server reports:
{
  "serverInfo": {
    "name": "my-mcp-server",     // ← set by you in code
    "version": "1.0.0"
  }
}

// mcp.json — THIS is what the client uses for the combined name:
{
  "mcpServers": {
    "My MCP Server": { ... }     // ← set by the customer, unknown to server
  }
}

The combined name My MCP Server: getFiles is constructed entirely on the client side. The server never sees the "My MCP Server" string.

Solution 1: Enforce short internal tool names (recommended)

Since you cannot control the customer's server name, the practical approach is to make your tool names short enough that even long server names stay under the limit:

// Target: max total length of 60
// Assume worst-case server name of 20 chars + " : " (3 chars) = 23 chars overhead
// So tool names must be ≤ 37 chars

const MAX_SERVER_NAME_OVERHEAD = 23; // " : " + estimated max server name
const CLIENT_TOOL_NAME_LIMIT = 60;

function registerToolSafely(server, name, handler) {
  if (name.length > CLIENT_TOOL_NAME_LIMIT - MAX_SERVER_NAME_OVERHEAD) {
    console.warn(
      `Tool "${name}" is ${name.length} chars. ` +
      `Combined name may exceed client limits if the server config name is long. ` +
      `Consider shortening to ≤ ${CLIENT_TOOL_NAME_LIMIT - MAX_SERVER_NAME_OVERHEAD} chars.`
    );
  }
  server.registerTool(name, handler);
}

This does not solve the root problem but prevents it reliably.

Solution 2: Document the limit for your customers

Add a section to your README or output a startup message:

WARNING: MCP clients (Cursor, Claude Desktop) limit combined tool names
to 60-64 characters. Combined name = "<your server name in mcp.json> : <tool name>".
Current tools: getFiles (8 chars), processLargeDocument (20 chars), ...
If you use a long server name, rename it in mcp.json.

Solution 3: Use serverInfo.name as a hint (partial workaround)

The serverInfo.name you set in your initialize handler is the "canonical" name. Some clients use this as the prefix instead of the mcp.json key. You can try setting it to match:

server.setRequestHandler("initialize", async (request) => ({
  serverInfo: {
    name: "shortname",    // ← use a short, fixed name
    version: "1.0.0"
  },
  capabilities: { tools: {} }
}));

But this is not reliable — different clients behave differently. Cursor uses the mcp.json key; Claude Desktop may use serverInfo.name; the behavior is not standardized.

Solution 4: Dynamic tool registration based on server metadata

The most robust approach: register a single meta-tool that the customer calls to get diagnostics:

server.registerTool("__diagnose_tool_names", async () => {
  const tools = await server.listTools();
  const warnings = [];
  for (const tool of tools.tools) {
    // Estimate: assume a generous max server name of 15 chars
    const estimatedTotal = 15 + 3 + tool.name.length;
    if (estimatedTotal > 60) {
      warnings.push(`\`${tool.name}\`: estimated combined length ~${estimatedTotal} (limit: 60)`);
    }
  }
  return {
    content: [{
      type: "text",
      text: warnings.length > 0
        ? `⚠️ Potential tool name length issues:\n${warnings.join('\n')}\n\nReduce the server name in mcp.json or shorten tool names.`
        : "✅ All tool names should be within limits."
    }]
  };
});

Bottom line

The server genuinely cannot discover the mcp.json key name — it is a client-side concept that MCP does not expose. The practical fix is to keep your tool names short (≤ 30-35 chars) and document the constraint for your customers. The __diagnose_tool_names meta-tool gives customers a way to self-check without you needing to know their config.