Logger

nc.logger prints readable, colored logs in development and structured JSON in production, with no setup. Its functions are also available at the top level: nc.info() is nc.logger.info().

nc.info("Server listening on port 3000");
nc.success("Database connected");
nc.warn("Cache is almost full");
nc.error(new Error("Payment failed"));

[14:30:05] ℹ INFO Server listening on port 3000
[14:30:05] ✔ OK Database connected
[14:30:05] ⚠ WARN Cache is almost full
[14:30:05] ✖ ERROR Payment failed
    at charge (/app/billing.js:42:11)

#Levels

From the most talkative to the most severe: trace, debug, info, warn, error, fatal. log and success print at the info level. Messages below the current level are dropped.

The default level is info, or debug when the DEBUG or NODE_DEBUG variable is set. Change it with LOG_LEVEL=warn, or in code:

nc.setLevel("debug");
nc.setLevel("silent"); // nothing at all

if (nc.isLevelEnabled("debug")) nc.debug(buildExpensiveReport());

warn, error and fatal go to stderr, the rest to stdout. fatal doesn't stop the process: call process.exit(1) if that's what you want.

#Errors and objects

Pass anything. Objects are pretty-printed, and errors show their stack trace and their chain of causes:

nc.info("user:", { id: 1, roles: ["admin"] });
nc.error(new Error("Cannot save order", { cause: dbError }));

#Markup

Style parts of a message with <% styles text %>:

nc.log("<% green bold ✔ Saved %> in <% dim 12ms %>");
nc.log("<% #ff8800 Orange %> on <% bg#1e1e2e white a dark background %>");

Any color or style from nc.color works, plus #hex, bg#hex, rgb(r, g, b) and bgRgb(r, g, b). If <% clashes with a template engine, change the delimiters with nc.setDelimiter({ open: "{{", close: "}}" }).

#Groups, timers and tables

nc.group("Deploy");
nc.info("Building");
nc.timeStart("upload");
await upload();
nc.timeEnd("upload"); // "upload: 1.24s"
nc.groupEnd();

nc.table([{ name: "Ada", role: "admin" }, { name: "Bob", role: "user" }]);
nc.box("Server ready\nhttp://localhost:3000", { title: "my-app", borderColor: "green" });
nc.divider("Results");

Every function returns the logger, so calls chain: nc.group("Startup").info("Loading config").

#Loggers with their own settings

createLogger() gives you an independent logger. child() creates one that shares the settings with a nested scope:

const log = nc.createLogger({ scope: "api", timestamp: "HH:mm:ss.SSS" });
log.info("GET /users 200");        // [14:30:05.120] [api] ℹ INFO GET /users 200

const db = log.child("db");        // scope "api:db"
db.debug("query took 12ms");

A child can carry its own fields. They're added to the parent's, which makes per-request loggers easy:

const reqLog = log.child("request", { fields: { requestId: req.id } });
reqLog.info("payment accepted");   // JSON records include requestId

#JSON logs for production

Set LOG_FORMAT=json, or pass format: "json", and each message becomes one JSON object per line, ready for Datadog, Loki, CloudWatch and friends:

const log = nc.createLogger({ format: "json", fields: { service: "billing", version: "2.3.0" } });
log.error("charge failed", { orderId: 42 }, error);

{"time":"2026-09-11T14:30:05.120Z","level":"error","service":"billing","version":"2.3.0","orderId":42,"err":{"name":"Error","message":"card declined","stack":"Error: card declined\n    at ..."},"msg":"charge failed"}

Plain objects in the arguments are merged into the record, errors go under err, and everything else becomes the message.

#Log files

Write every message to a file as well, with rotation by size:

nc.configure({ file: { path: "logs/app.log", maxSize: "10MB", maxFiles: 5 } });

Colors are removed in files. When app.log passes 10 MB it becomes app.log.1, and the oldest file beyond five is deleted.

#Settings at a glance

configure() and createLogger() accept level, scope, timestamp (true, false or a time.format pattern), format, colors, file, fields, delimiter, and stdout/stderr streams. Colors turn off by themselves when the output isn't a terminal or when NO_COLOR is set.