Uses notifications/message for logging, not console.log

MCP defines a structured logging protocol via notifications/message with severity levels (debug, info, warning, error, etc.) that clients can display, filter, and route to observability systems. A server that only uses console.error keeps all operational visibility on stderr — invisible to the connected AI client and to any MCP-aware monitoring tool. When a server-side failure occurs during an agentic run, the client has no programmatic signal to surface the failure; the AI sees only the missing tool result with no explanation.

Use server.sendLoggingMessage() for events the client should see. Keep console.error for local debugging only.

// src/utils/logger.ts — MCP-native logging
import { server } from '../index.js'  // your McpServer instance

export function log(level: 'info' | 'warning' | 'error', message: string) {
  server.sendLoggingMessage({ level, logger: 'my-server', data: message })
}

// In tool handlers:
log('info', 'Connected to database successfully')
log('error', `Failed to connect: ${error.message}`)  // client sees this

Declare logging: {} in your server capabilities so clients know to expect log messages.