Bulk tool registration causes EventEmitter memory leak warnings

[cameroncooke]

Problem Description

When registering many tools dynamically (80+ tools), the MCP SDK triggers EventEmitter memory leak warnings due to individual sendToolListChanged() calls per tool registration.

Root Cause

• Each server.tool() call automatically triggers sendToolListChanged()
• Rapid notifications overwhelm stdout buffer in StdioServerTransport
• Multiple 'drain' listeners accumulate temporarily, exceeding Node.js default limit (10)

Stack Trace

MaxListenersExceededWarning: Possible EventEmitter memory leak detected. 11 drain listeners added to [Socket]. MaxListeners is 10.
    at genericNodeError (node:internal/errors:983:15)
    at wrappedFn (node:internal/errors:537:14)
    at _addListener (node:events:581:17)
    at Socket.addListener (node:events:599:10)
    at Readable.on (node:internal/streams/readable:1131:35)
    at Socket.once (node:events:643:8)
    at StdioServerTransport.send (/@modelcontextprotocol/sdk/dist/esm/server/stdio.js:73:30)
    at Promise.resolve.then.then._a (/@modelcontextprotocol/sdk/dist/esm/shared/protocol.js:151:83)

Reproduction Steps

1. Create an MCP server with dynamic tool registration
2. Register 80+ tools rapidly in a loop:

   for (const tool of manyTools) {
     server.tool(tool.name, tool.description, tool.schema, tool.handler);
   }

3. Observe EventEmitter memory leak warnings in stderr

Expected Behavior

• Bulk tool registration should not trigger memory leak warnings
• Efficient batch operations without notification spam

Current Workaround

// Increase maxListeners before bulk registration
process.stdout.setMaxListeners(100);

Proposed Solutions

1. Batch Notification API: Add optional defer parameter to tool() method
2. Bulk Registration: Add registerTools(tools[]) method with single notification
3. Increase Default MaxListeners: Set higher default for stdio transport
4. Documentation: Document bulk registration patterns and best practices

Use Case

Servers like XcodeBuildMCP that load 80+ tools dynamically based on user context need efficient bulk registration without warning spam. Dynamic tool loading is becoming common for context-aware MCP servers.

Environment

• MCP SDK Version: 1.17.1
• Node.js Version: 18+
• Transport: StdioServerTransport
• Platform: macOS/Linux

Impact

• False positive memory leak warnings confuse developers
• Performance degradation from stdout buffer backpressure
• Client receives excessive individual ToolListChangedNotification messages

The core issue is that the MCP SDK wasn't designed for bulk tool registration scenarios common in dynamic, context-aware servers.