export enum LogLevel {
ERROR = 0,
WARN = 1,
INFO = 2,
DEBUG = 3,
}
export interface LogEntry {
timestamp: string;
level: string;
message: string;
context: Record<string, unknown> | undefined;
error: {
name: string;
message: string;
stack?: string;
} | undefined;
}
export class Logger {
private level: LogLevel;
private format: 'json' | 'text';
constructor(level: 'error' | 'warn' | 'info' | 'debug' = 'info', format: 'json' | 'text' = 'text') {
this.level = LogLevel[level.toUpperCase() as keyof typeof LogLevel];
this.format = format;
}
private shouldLog(level: LogLevel): boolean {
return level <= this.level;
}
private formatMessage(entry: LogEntry): string {
if (this.format === 'json') {
return JSON.stringify(entry);
}
const { timestamp, level, message, context, error } = entry;
let output = `[${timestamp}] ${level.toUpperCase()}: ${message}`;
if (context && Object.keys(context).length > 0) {
output += ` ${JSON.stringify(context)}`;
}
if (error) {
output += `\nError: ${error.name}: ${error.message}`;
if (error.stack) {
output += `\n${error.stack}`;
}
}
return output;
}
private log(level: LogLevel, levelName: string, message: string, context?: Record<string, unknown>, error?: Error): void {
if (!this.shouldLog(level)) {
return;
}
const entry: LogEntry = {
timestamp: new Date().toISOString(),
level: levelName,
message,
context,
error: error ? {
name: error.name,
message: error.message,
...(error.stack && { stack: error.stack }),
} : undefined,
};
const output = this.formatMessage(entry);
// Write to stderr only (MCP uses stdout for protocol communication)
process.stderr.write(output + '\n');
}
error(message: string, context?: Record<string, unknown>, error?: Error): void {
this.log(LogLevel.ERROR, 'error', message, context, error);
}
warn(message: string, context?: Record<string, unknown>): void {
this.log(LogLevel.WARN, 'warn', message, context);
}
info(message: string, context?: Record<string, unknown>): void {
this.log(LogLevel.INFO, 'info', message, context);
}
debug(message: string, context?: Record<string, unknown>): void {
this.log(LogLevel.DEBUG, 'debug', message, context);
}
child(context: Record<string, unknown>): Logger {
const childLogger = new Logger(
Object.keys(LogLevel)[this.level] as 'error' | 'warn' | 'info' | 'debug',
this.format
);
const originalLog = childLogger.log.bind(childLogger);
const boundLog = (level: LogLevel, levelName: string, message: string, messageContext?: Record<string, unknown>, error?: Error): void => {
const mergedContext = { ...context, ...messageContext };
originalLog(level, levelName, message, mergedContext, error);
};
(childLogger as any).log = boundLog;
return childLogger;
}
}
