/**
* Structured logging utility for MCP server
* Supports JSON and pretty formats with configurable log levels
*/
type LogLevel = "debug" | "info" | "warn" | "error";
interface LogContext {
[key: string]: unknown;
}
class Logger {
private level: LogLevel;
private format: "json" | "pretty";
constructor() {
const envLevel = (process.env.LOG_LEVEL || "info").toLowerCase() as LogLevel;
const validLevels: LogLevel[] = ["debug", "info", "warn", "error"];
this.level = validLevels.includes(envLevel) ? envLevel : "info";
const envFormat = (process.env.LOG_FORMAT || "pretty").toLowerCase();
this.format = envFormat === "json" ? "json" : "pretty";
}
private shouldLog(level: LogLevel): boolean {
const levels: Record<LogLevel, number> = {
debug: 0,
info: 1,
warn: 2,
error: 3,
};
return levels[level] >= levels[this.level];
}
private formatMessage(
level: LogLevel,
message: string,
context?: LogContext
): string {
const timestamp = new Date().toISOString();
const logEntry = {
timestamp,
level,
message,
...context,
};
if (this.format === "json") {
return JSON.stringify(logEntry);
}
// Pretty format
const contextStr = context
? ` ${Object.entries(context)
.map(([k, v]) => `${k}=${JSON.stringify(v)}`)
.join(" ")}`
: "";
return `[${timestamp}] ${level.toUpperCase()}: ${message}${contextStr}`;
}
debug(message: string, context?: LogContext): void {
if (this.shouldLog("debug")) {
console.debug(this.formatMessage("debug", message, context));
}
}
info(message: string, context?: LogContext): void {
if (this.shouldLog("info")) {
console.info(this.formatMessage("info", message, context));
}
}
warn(message: string, context?: LogContext): void {
if (this.shouldLog("warn")) {
console.warn(this.formatMessage("warn", message, context));
}
}
error(message: string, error?: Error | unknown, context?: LogContext): void {
if (this.shouldLog("error")) {
const errorContext: LogContext = {
...context,
};
if (error instanceof Error) {
errorContext.error = {
name: error.name,
message: error.message,
stack: error.stack,
};
} else if (error !== undefined) {
errorContext.error = String(error);
}
console.error(this.formatMessage("error", message, errorContext));
}
}
}
export const logger = new Logger();
