import winston from 'winston';
/**
* Structured logging with Winston
*/
const logLevel = process.env.LOG_LEVEL || 'info';
export const logger = winston.createLogger({
level: logLevel,
format: winston.format.combine(
winston.format.timestamp(),
winston.format.errors({ stack: true }),
winston.format.json()
),
defaultMeta: { service: 'mcp-bigquery-server' },
transports: [
// Console transport - write to stderr for MCP stdio compatibility
// Per MCP best practices: avoid writing to stdout as it can corrupt JSON-RPC messages
new winston.transports.Console({
stderrLevels: ['error', 'warn', 'info', 'debug', 'verbose', 'silly'], // All logs to stderr
format: winston.format.combine(
winston.format.colorize(),
winston.format.printf((info) => {
const { timestamp, level, message, ...meta } = info;
const metaStr = Object.keys(meta).length ? JSON.stringify(meta, null, 2) : '';
return `${String(timestamp)} [${String(level)}]: ${String(message)} ${metaStr}`;
})
),
}),
],
});
// Add file transport in production
if (process.env.NODE_ENV === 'production') {
logger.add(
new winston.transports.File({
filename: 'logs/error.log',
level: 'error',
maxsize: 5242880, // 5MB
maxFiles: 5,
})
);
logger.add(
new winston.transports.File({
filename: 'logs/combined.log',
maxsize: 5242880, // 5MB
maxFiles: 5,
})
);
}
export default logger;
