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pino([options], [destination]) => logger

The exported pino function takes two optional arguments, options and destination and returns a logger instance.

options (Object)

name (String)

Default: undefined

The name of the logger. When set adds a name field to every JSON line logged.

level (String)

Default: 'info'

One of 'fatal', 'error', 'warn', 'info', 'debug', 'trace' or 'silent'.

Additional levels can be added to the instance via the customLevels option.

customLevels (Object)

Default: undefined

Use this option to define additional logging levels. The keys of the object correspond the namespace of the log level, and the values should be the numerical value of the level.

const logger = pino({
  customLevels: {
    foo: 35

useOnlyCustomLevels (Boolean)

Default: false

Use this option to only use defined customLevels and omit Pino's levels. Logger's default level must be changed to a value in customLevels in order to use useOnlyCustomLevels Warning: this option may not be supported by downstream transports.

const logger = pino({
  customLevels: {
    foo: 35
  useOnlyCustomLevels: true,
  level: 'foo'
})'hi')'hello') // Will throw an error saying info in not found in logger object

mixin (Function):

Default: undefined

If provided, the mixin function is called each time one of the active logging methods is called. The first and only parameter is the value mergeObject or an empty object. The function must synchronously return an object. The properties of the returned object will be added to the logged JSON.

let n = 0
const logger = pino({
  mixin () {
    return { line: ++n }
// {"level":30,"time":1573664685466,"pid":78742,"hostname":"x","line":1,"msg":"hello"}'world')
// {"level":30,"time":1573664685469,"pid":78742,"hostname":"x","line":2,"msg":"world"}

The result of mixin() is supposed to be a new object. For performance reason, the object returned by mixin() will be mutated by pino. In the following example, passing mergingObject argument to the first info call will mutate the global mixin object:

const mixin = {
    appName: 'My app'

const logger = pino({
    mixin() {
        return mixin;
    description: 'Ok'
}, 'Message 1')
// {"level":30,"time":1591195061437,"pid":16012,"hostname":"x","appName":"My app","description":"Ok" "msg":"Message 1"}'Message 2')
// {"level":30,"time":1591195061437,"pid":16012,"hostname":"x","appName":"My app","description":"Ok","msg":"Message 2"}
// Note: the second log contains "description":"Ok" text, even if it was not provided.

If the mixin feature is being used merely to add static metadata to each log message, then a child logger β‡— should be used instead.

redact (Array | Object):

Default: undefined

As an array, the redact option specifies paths that should have their values redacted from any log output.

Each path must be a string using a syntax which corresponds to JavaScript dot and bracket notation.

If an object is supplied, three options can be specified:

  • paths (array): Required. An array of paths. See redaction - Path Syntax β‡— for specifics.
  • censor (String|Function|Undefined): Optional. When supplied as a String the censor option will overwrite keys which are to be redacted. When set to undefined the key will be removed entirely from the object. The censor option may also be a mapping function. The (synchronous) mapping function has the signature (value, path) => redactedValue and is called with the unredacted value and path to the key being redacted, as an array. For example given a redaction path of a.b.c the path argument would be ['a', 'b', 'c']. The value returned from the mapping function becomes the applied censor value. Default: '[Redacted]' value synchronously. Default: '[Redacted]'
  • remove (Boolean): Optional. Instead of censoring the value, remove both the key and the value. Default: false

WARNING: Never allow user input to define redacted paths.

hooks (Object)

An object mapping to hook functions. Hook functions allow for customizing internal logger operations. Hook functions must be synchronous functions.


Allows for manipulating the parameters passed to logger methods. The signature for this hook is logMethod (args, method, level) {}, where args is an array of the arguments that were passed to the log method and method is the log method itself, level is the log level itself. This hook must invoke the method function by using apply, like so: method.apply(this, newArgumentsArray).

For example, Pino expects a binding object to be the first parameter with an optional string message as the second parameter. Using this hook the parameters can be flipped:

const hooks = {
  logMethod (inputArgs, method, level) {
    if (inputArgs.length >= 2) {
      const arg1 = inputArgs.shift()
      const arg2 = inputArgs.shift()
      return method.apply(this, [arg2, arg1, ...inputArgs])
    return method.apply(this, inputArgs)

formatters (Object)

An object containing functions for formatting the shape of the log lines. These functions should return a JSONifiable object and should never throw. These functions allow for full customization of the resulting log lines. For example, they can be used to change the level key name or to enrich the default metadata.


Changes the shape of the log level. The default shape is { level: number }. The function takes two arguments, the label of the level (e.g. 'info') and the numeric value (e.g. 30).

const formatters = {
  level (label, number) {
    return { level: number }

Changes the shape of the bindings. The default shape is { pid, hostname }. The function takes a single argument, the bindings object. It will be called every time a child logger is created.

const formatters = {
  bindings (bindings) {
    return { pid:, hostname: bindings.hostname }

Changes the shape of the log object. This function will be called every time one of the log methods (such as .info) is called. All arguments passed to the log method, except the message, will be pass to this function. By default it does not change the shape of the log object.

const formatters = {
  log (object) {
    return object

serializers (Object)

Default: {err: pino.stdSerializers.err}

An object containing functions for custom serialization of objects. These functions should return an JSONifiable object and they should never throw. When logging an object, each top-level property matching the exact key of a serializer will be serialized using the defined serializer.

serializers[Symbol.for('pino.*')] (Function) - DEPRECATED

Use formatters.log instead.

base (Object)

Default: {pid:, hostname: os.hostname}

Key-value object added as child logger to each log line.

Set to null to avoid adding pid, hostname and name properties to each log.

enabled (Boolean)

Default: true

Set to false to disable logging.

crlf (Boolean)

Default: false

Set to true to logs newline delimited JSON with \r\n instead of \n.

timestamp (Boolean | Function)

Default: true

Enables or disables the inclusion of a timestamp in the log message. If a function is supplied, it must synchronously return a partial JSON string representation of the time, e.g. ,"time":1493426328206 (which is the default).

If set to false, no timestamp will be included in the output.

See stdTimeFunctions for a set of available functions for passing in as a value for this option.


timestamp: () => `,"time":"${new Date(}"`
// which is equivalent to:
// timestamp: stdTimeFunctions.isoTime

Caution: attempting to format time in-process will significantly impact logging performance.

messageKey (String)

Default: 'msg'

The string key for the 'message' in the JSON object.

nestedKey (String)

Default: null

If there's a chance that objects being logged have properties that conflict with those from pino itself (level, timestamp, pid, etc) and duplicate keys in your log records are undesirable, pino can be configured with a nestedKey option that causes any objects that are logged to be placed under a key whose name is the value of nestedKey.

This way, when searching something like Kibana for values, one can consistently search under the configured nestedKey value instead of the root log record keys.

For example,

const logger = require('pino')({
  nestedKey: 'payload'

const thing = { level: 'hi', time: 'never', foo: 'bar'} // has pino-conflicting properties!

// logs the following:
// {"level":30,"time":1578357790020,"pid":91736,"hostname":"x","payload":{"level":"hi","time":"never","foo":"bar"}}

In this way, logged objects' properties don't conflict with pino's standard logging properties, and searching for logged objects can start from a consistent path.

prettyPrint (Boolean | Object)

Default: false

Enables pretty printing log logs. This is intended for non-production configurations. This may be set to a configuration object as outlined in the pino-pretty documentation.

The options object may additionally contain a prettifier property to define which prettifier module to use. When not present, prettifier defaults to 'pino-pretty'. Regardless of the value, the specified prettifier module must be installed as a separate dependency:

npm install pino-pretty

useLevelLabels (Boolean) - DEPRECATED

Use formatters.level instead. This will be removed in v7.

changeLevelName (String) - DEPRECATED

Use formatters.level instead. This will be removed in v7.

levelKey (String) - DEPRECATED

Use formatters.level instead. This will be removed in v7.

browser (Object)

Browser only, may have asObject and write keys. This option is separately documented in the Browser API β‡— documentation.

destination (SonicBoom | WritableStream | String | Object)

Default: pino.destination(1) (STDOUT)

The destination parameter, at a minimum must be an object with a write method. An ordinary Node.js stream can be passed as the destination (such as the result of fs.createWriteStream) but for peak log writing performance it is strongly recommended to use pino.destination to create the destination stream.

// pino.destination(1) by default
const stdoutLogger = require('pino')()

// destination param may be in first position when no options:
const fileLogger = require('pino')( pino.destination('/log/path'))

// use the stderr file handle to log to stderr:
const opts = {name: 'my-logger'}
const stderrLogger = require('pino')(opts, pino.destination(2))

// automatic wrapping in pino.destination
const fileLogger = require('pino')('/log/path')

// Asynchronous logging
const fileLogger = pino(pino.destination({ dest: '/log/path', sync: false }))

However, there are some special instances where pino.destination is not used as the default:

  • When something, e.g a process manager, has monkey-patched process.stdout.write.

In these cases process.stdout is used instead.


Default: false

Using the global symbol Symbol.for('pino.metadata') as a key on the destination parameter and setting the key it to true, indicates that the following properties should be set on the destination object after each log line is written:

  • the last logging level as destination.lastLevel
  • the last logging message as destination.lastMsg
  • the last logging object as destination.lastObj
  • the last time as destination.lastTime, which will be the partial string returned by the time function.
  • the last logger instance as destination.lastLogger (to support child loggers)

For a full reference for using Symbol.for('pino.metadata'), see the pino-multi-stream β‡— module.

The following is a succinct usage example:

const dest = pino.destination('/dev/null')
dest[Symbol.for('pino.metadata')] = true
const logger = pino(dest){a: 1}, 'hi')
const { lastMsg, lastLevel, lastObj, lastTime} = dest
  'Logged message "%s" at level %d with object %o at time %s',
  lastMsg, lastLevel, lastObj, lastTime
) // Logged message "hi" at level 30 with object { a: 1 } at time 1531590545089

Logger Instance

The logger instance is the object returned by the main exported pino function.

The primary purpose of the logger instance is to provide logging methods.

The default logging methods are trace, debug, info, warn, error, and fatal.

Each logging method has the following signature: ([mergingObject], [message], [...interpolationValues]).

The parameters are explained below using the method but the same applies to all logging methods.

Logging Method Parameters

mergingObject (Object)

An object can optionally be supplied as the first parameter. Each enumerable key and value of the mergingObject is copied in to the JSON log line.{MIX: {IN: true}})
// {"level":30,"time":1531254555820,"pid":55956,"hostname":"x","MIX":{"IN":true}}

message (String)

A message string can optionally be supplied as the first parameter, or as the second parameter after supplying a mergingObject.

By default, the contents of the message parameter will be merged into the JSON log line under the msg key:'hello world')
// {"level":30,"time":1531257112193,"msg":"hello world","pid":55956,"hostname":"x"}

The message parameter takes precedence over the mergedObject. That is, if a mergedObject contains a msg property, and a message parameter is supplied in addition, the msg property in the output log will be the value of the message parameter not the value of the msg property on the mergedObject. See Avoid Message Conflict for information on how to overcome this limitation.

The messageKey option can be used at instantiation time to change the namespace from msg to another string as preferred.

The message string may contain a printf style string with support for the following placeholders:

  • %s – string placeholder
  • %d – digit placeholder
  • %O, %o and %j – object placeholder

Values supplied as additional arguments to the logger method will then be interpolated accordingly.

...interpolationValues (Any)

All arguments supplied after message are serialized and interpolated according to any supplied printf-style placeholders (%s, %d, %o|%O|%j) to form the final output msg value for the JSON log line.'%o hello %s', {worldly: 1}, 'world')
// {"level":30,"time":1531257826880,"msg":"{\"worldly\":1} hello world","pid":55956,"hostname":"x"}

Since pino v6, we do not automatically concatenate and cast to string consecutive parameters:'hello', 'world')
// {"level":30,"time":1531257618044,"msg":"hello","pid":55956,"hostname":"x"}
// world is missing

However, it's possible to inject a hook to modify this behavior:

const pinoOptions = {
  hooks: { logMethod }

function logMethod (args, method) {
  if (args.length === 2) {
    args[0] = `${args[0]} %j`
  method.apply(this, args)

const logger = pino(pinoOptions)


Errors can be supplied as either the first parameter or if already using mergingObject then as the err property on the mergingObject.


This section describes the default configuration. The error serializer can be mapped to a different key using the serializers option. Error("test"))
// {"level":30,"time":1531257618044,"msg":"test","stack":"...","type":"Error","pid":55956,"hostname":"x"}{ err: new Error("test"), otherkey: 123 }, "some text")
// {"level":30,"time":1531257618044,"err":{"msg": "test", "stack":"...","type":"Error"},"msg":"some text","pid":55956,"hostname":"x","otherkey":123}

logger.trace([mergingObject], [message], [...interpolationValues])

Write a 'trace' level log, if the configured level allows for it.

logger.debug([mergingObject], [message], [...interpolationValues])

Write a 'debug' level log, if the configured level allows for it.[mergingObject], [message], [...interpolationValues])

Write an 'info' level log, if the configured level allows for it.

logger.warn([mergingObject], [message], [...interpolationValues])

Write a 'warn' level log, if the configured level allows for it.

logger.error([mergingObject], [message], [...interpolationValues])

Write a 'error' level log, if the configured level allows for it.

logger.fatal([mergingObject], [message], [...interpolationValues])

Write a 'fatal' level log, if the configured level allows for it.

Since 'fatal' level messages are intended to be logged just prior to the process exiting the fatal method will always sync flush the destination. Therefore it's important not to misuse fatal since it will cause performance overhead if used for any other purpose than writing final log messages before the process crashes or exits.


Noop function.

logger.child(bindings) => logger

The logger.child method allows for the creation of stateful loggers, where key-value pairs can be pinned to a logger causing them to be output on every log line.

Child loggers use the same output stream as the parent and inherit the current log level of the parent at the time they are spawned.

The log level of a child is mutable. It can be set independently of the parent either by setting the level accessor after creating the child logger or using the reserved bindings.level key.

bindings (Object)

An object of key-value pairs to include in every log line output via the returned child logger.

const child = logger.child({ MIX: {IN: 'always'} })'hello')
// {"level":30,"time":1531258616689,"msg":"hello","pid":64849,"hostname":"x","MIX":{"IN":"always"}}'child!')
// {"level":30,"time":1531258617401,"msg":"child!","pid":64849,"hostname":"x","MIX":{"IN":"always"}}

The bindings object may contain any key except for reserved configuration keys level and serializers.

bindings.level (String)

If a level property is present in the bindings object passed to logger.child it will override the child logger level.

const logger = pino()
logger.debug('nope') // will not log, since default level is info
const child = logger.child({foo: 'bar', level: 'debug'})
child.debug('debug!') // will log as the `level` property set the level to debug
bindings.serializers (Object)

Child loggers inherit the serializers from the parent logger.

Setting the serializers key of the bindings object will override any configured parent serializers.

const logger = require('pino')(){test: 'will appear'})
// {"level":30,"time":1531259759482,"pid":67930,"hostname":"x","test":"will appear"}
const child = logger.child({serializers: {test: () => `child-only serializer`}}){test: 'will be overwritten'})
// {"level":30,"time":1531259784008,"pid":67930,"hostname":"x","test":"child-only serializer"}


Returns an object containing all the current bindings, cloned from the ones passed in via logger.child().

const child = logger.child({ foo: 'bar' })
// { foo: 'bar' }
const anotherChild = child.child({ MIX: { IN: 'always' } })
// { foo: 'bar', MIX: { IN: 'always' } }


Flushes the content of the buffer when using pino.destination({ sync: false }).

This is an asynchronous, fire and forget, operation.

The use case is primarily for asynchronous logging, which may buffer log lines while others are being written. The logger.flush method can be used to flush the logs on a long interval, say ten seconds. Such a strategy can provide an optimum balance between extremely efficient logging at high demand periods and safer logging at low demand periods.

logger.level (String) [Getter/Setter]

Set this property to the desired logging level.

The core levels and their values are as follows:

Level: trace debug info warn error fatal silent
Value: 10 20 30 40 50 60 Infinity

The logging level is a minimum level based on the associated value of that level.

For instance if logger.level is info (30) then info (30), warn (40), error (50) and fatal (60) log methods will be enabled but the trace (10) and debug (20) methods, being less than 30, will not.

The silent logging level is a specialized level which will disable all logging, the silent log method is a noop function.


A utility method for determining if a given log level will write to the destination.

level (String)

The given level to check against:

if (logger.isLevelEnabled('debug')) logger.debug('conditional log')

levelLabel (String)

Defines the method name of the new level.

levelValue (Number)

Defines the associated minimum threshold value for the level, and therefore where it sits in order of priority among other levels.

logger.levelVal (Number)

Supplies the integer value for the current logging level.

if (logger.levelVal === 30) {
  console.log('logger level is `info`')

logger.levels (Object)

Levels are mapped to values to determine the minimum threshold that a logging method should be enabled at (see logger.level).

The logger.levels property holds the mappings between levels and values, and vice versa.

$ node -p "require('pino')().levels"
{ labels:
   { '10': 'trace',
     '20': 'debug',
     '30': 'info',
     '40': 'warn',
     '50': 'error',
     '60': 'fatal' },
   { fatal: 60, error: 50, warn: 40, info: 30, debug: 20, trace: 10 } }


Returns the serializers as applied to the current logger instance. If a child logger did not register it's own serializer upon instantiation the serializers of the parent will be returned.

Event: 'level-change'

The logger instance is also an EventEmitter β‡—

A listener function can be attached to a logger via the level-change event

The listener is passed four arguments:

  • levelLabel – the new level string, e.g trace
  • levelValue – the new level number, e.g 10
  • previousLevelLabel – the prior level string, e.g info
  • previousLevelValue – the prior level numbebr, e.g 30
const logger = require('pino')()
logger.on('level-change', (lvl, val, prevLvl, prevVal) => {
  console.log('%s (%d) was changed to %s (%d)', prevLvl, prevVal, lvl, val)
logger.level = 'trace' // trigger event

Please note that due to a known bug, every logger.child() call will fire a level-change event. These events can be ignored by writing an event handler like:

const logger = require('pino')()
logger.on('level-change', function (lvl, val, prevLvl, prevVal) {
  if (logger !== this) {
  console.log('%s (%d) was changed to %s (%d)', prevLvl, prevVal, lvl, val)
logger.child({}); // trigger an event by creating a child instance, notice no console.log
logger.level = 'trace' // trigger event using actual value change, notice console.log

logger.version (String)

Exposes the Pino package version. Also available on the exported pino function.


pino.destination([opts]) => SonicBoom

Create a Pino Destination instance: a stream-like object with significantly more throughput (over 30%) than a standard Node.js stream.

const pino = require('pino')
const logger = pino(pino.destination('./my-file'))
const logger2 = pino(pino.destination())
const logger3 = pino(pino.destination({
  dest: './my-file',
  minLength: 4096, // Buffer before writing
  sync: false // Asynchronous logging

The pino.destination method may be passed a file path or a numerical file descriptor. By default, pino.destination will use process.stdout.fd (1) as the file descriptor.

pino.destination is implemented on sonic-boom β‡—.

A pino.destination instance can also be used to reopen closed files (for example, for some log rotation scenarios), see Reopening log files., [handler]) => Function | FinalLogger

The method can be used to acquire a final logger instance or create an exit listener function.

The finalLogger is a specialist logger that synchronously flushes on every write. This is important to guarantee final log writes, when using pino.destination({ sync: false }) target.

Since final log writes cannot be guaranteed with normal Node.js streams, if the destination parameter of the logger supplied to is a Node.js stream will throw.

The use of with pino.destination is not needed, as pino.destination writes things synchronously., handler) => Function

In this case the method supplies an exit listener function that can be supplied to process exit events such as exit, uncaughtException, SIGHUP and so on.

The exit listener function will call the supplied handler function with an error object (or else null), a finalLogger instance followed by any additional arguments the handler may be called with.

process.on('uncaughtException',, (err, finalLogger) => {
  finalLogger.error(err, 'uncaughtException')
})) => FinalLogger

In this case the method returns a finalLogger instance.

var finalLogger ='exiting...')

pino.stdSerializers (Object)

The pino.stdSerializers object provides functions for serializing objects common to many projects. The standard serializers are directly imported from pino-std-serializers.

pino.stdTimeFunctions (Object)

The timestamp option can accept a function which determines the timestamp value in a log line.

The pino.stdTimeFunctions object provides a very small set of common functions for generating the timestamp property. These consist of the following

  • pino.stdTimeFunctions.epochTime: Milliseconds since Unix epoch (Default)

  • pino.stdTimeFunctions.unixTime: Seconds since Unix epoch

  • pino.stdTimeFunctions.nullTime: Clears timestamp property (Used when timestamp: false)

  • pino.stdTimeFunctions.isoTime: ISO 8601-formatted time in UTC

  • See timestamp option

pino.symbols (Object)

For integration purposes with ecosystem and third party libraries pino.symbols exposes the symbols used to hold non-public state and methods on the logger instance.

Access to the symbols allows logger state to be adjusted, and methods to be overridden or proxied for performant integration where necessary.

The pino.symbols object is intended for library implementers and shouldn't be utilized for general use.

pino.version (String)

Exposes the Pino package version. Also available on the logger instance.