pino-pretty

What is pino-pretty?

The pino-pretty npm package is a module that can be used to format logs produced by Pino, a Node.js logging library. It takes raw log lines in JSON format and transforms them into a more human-readable form. This is particularly useful during development when you need to quickly understand log output.

What are pino-pretty's main functionalities?

Pretty Printing

This feature allows you to format your logs in a more readable way, with options such as colorization for different log levels.

const pino = require('pino');
const pretty = require('pino-pretty');
const stream = pretty({ colorize: true });
const logger = pino(stream);
logger.info('This is a pretty-printed log message.');

Custom Log Formatting

Pino-pretty allows for custom log formatting, including options to translate timestamps and ignore certain fields.

const pino = require('pino');
const pretty = require('pino-pretty');
const stream = pretty({
  translateTime: 'SYS:standard',
  ignore: 'pid,hostname'
});
const logger = pino(stream);
logger.info('Custom formatted log message.');

Integration with Pino Logger

Pino-pretty can be seamlessly integrated with Pino logger to provide pretty-printing capabilities directly within the logger configuration.

const pino = require('pino');
const logger = pino({
  prettyPrint: {
    colorize: true
  }
});
logger.info('Integrated pino-pretty with Pino logger.');

Other packages similar to pino-pretty

bunyan

Bunyan is a simple and fast JSON logging library for node.js services. It comes with a CLI tool for pretty-printing bunyan log output. Compared to pino-pretty, Bunyan provides its own logging capabilities, whereas pino-pretty is specifically designed to format Pino logs.

winston

Winston is a multi-transport async logging library for Node.js. It supports custom formatting and multiple logging transports. Unlike pino-pretty, which is focused on pretty-printing, Winston offers a broader set of logging features including transports for logging to various outputs.

morgan

Morgan is an HTTP request logger middleware for Node.js. It can format logs in predefined or custom formats. While morgan is used for logging HTTP requests in web applications, pino-pretty is used for general purpose log formatting.

README

pino-pretty

This module provides a basic ndjson formatter to be used in development. If an incoming line looks like it could be a log line from an ndjson logger, in particular the Pino logging library, then it will apply extra formatting by considering things like the log level and timestamp.

A standard Pino log line like:

{"level":30,"time":1522431328992,"msg":"hello world","pid":42,"hostname":"foo","v":1}

Will format to:

[17:35:28.992] INFO (42): hello world

If you landed on this page due to the deprecation of the prettyPrint option of pino, read the Programmatic Integration section.

Example

Using the example script from the Pino module, we can see what the prettified logs will look like:

Install

$ npm install -g pino-pretty

Usage

It is recommended to use pino-pretty with pino by piping output to the CLI tool:

node app.js | pino-pretty

CLI Arguments

• --colorize (-c): Adds terminal color escape sequences to the output.
• --colorizeObjects (-C): Allows suppressing colorization of objects when set to false. In combination with --singleLine, this ensures that the end of each line is parsable JSON.
• --crlf (-f): Appends carriage return and line feed, instead of just a line feed, to the formatted log line.
• --errorProps (-e): When formatting an error object, display this list of properties. The list should be a comma-separated list of properties Default: ''. Do not use this option if logging from pino@7. Support will be removed from future verions.
• --levelFirst (-l): Display the log level name before the logged date and time.
• --errorLikeObjectKeys (-k): Define the log keys that are associated with error like objects. Default: err,error.
• --messageKey (-m): Define the key that contains the main log message. Default: msg.
• --levelKey (--levelKey): Define the key that contains the level of the log. Nested keys are supported with each property delimited by a dot character (.). Keys may be escaped to target property names that contains the delimiter itself: (--levelKey tags\\.level). Default: level.
• --levelLabel (-b): Output the log level using the specified label. Default: levelLabel.
• --minimumLevel (-L): Hide messages below the specified log level. Accepts a number, trace, debug, info, warn, error, or fatal. If any more filtering is required, consider using jq.
• --customLevels (-x): Override default levels with custom levels, e.g. -x err:99,info:1
• --customColors (-X): Override default colors with custom colors, e.g. -X err:red,info:blue
• --useOnlyCustomProps (-U): Only use custom levels and colors (if provided) (default: true); else fallback to default levels and colors, e.g. -U false
• --messageFormat (-o): Format output of message, e.g. {levelLabel} - {pid} - url:{req.url} will output message: INFO - 1123 - url:localhost:3000/test Default: false
• --timestampKey (-a): Define the key that contains the log timestamp. Default: time.
• --translateTime (-t): Translate the epoch time value into a human-readable date and time string. This flag also can set the format string to apply when translating the date to a human-readable format. For a list of available pattern letters, see the dateformat documentation.
  • The default format is HH:MM:ss.l in the local timezone.
  • Require a UTC: prefix to translate time to UTC, e.g. UTC:yyyy-mm-dd HH:MM:ss.l o.
  • Require a SYS: prefix to translate time to the local system's time zone. A shortcut SYS:standard to translate time to yyyy-mm-dd HH:MM:ss.l o in system time zone.
• --ignore (-i): Ignore one or several keys, nested keys are supported with each property delimited by a dot character (.), keys may be escaped to target property names that contains the delimiter itself: (-i time,hostname,req.headers,log\\.domain\\.corp/foo). The --ignore option would be ignored, if both --ignore and --include are passed. Default: hostname.
• --include (-I): The opposite of --ignore. Include one or several keys.
• --hideObject (-H): Hide objects from output (but not error object)
• --singleLine (-S): Print each log message on a single line (errors will still be multi-line)
• --config: Specify a path to a config file containing the pino-pretty options. pino-pretty will attempt to read from a .pino-prettyrc in your current directory (process.cwd) if not specified

Programmatic Integration

We recommend against using pino-pretty in production and highly recommend installing pino-pretty as a development dependency.

Install pino-pretty alongside pino and set the transport target to 'pino-pretty':

const pino = require('pino')
const logger = pino({
  transport: {
    target: 'pino-pretty'
  },
})

logger.info('hi')

The transport option can also have an options object containing pino-pretty options:

const pino = require('pino')
const logger = pino({
  transport: {
    target: 'pino-pretty',
    options: {
      colorize: true
    }
  }
})

logger.info('hi')

Use it as a stream:

const pino = require('pino')
const pretty = require('pino-pretty')
const logger = pino(pretty())

logger.info('hi')

Options are also supported:

const pino = require('pino')
const pretty = require('pino-pretty')
const stream = pretty({
  colorize: true
})
const logger = pino(stream)

logger.info('hi')

See the Options section for all possible options.

Usage as a stream

If you are using pino-pretty as a stream and you need to provide options to pino, pass the options as the first argument and pino-pretty as second argument:

const pino = require('pino')
const pretty = require('pino-pretty')
const stream = pretty({
  colorize: true
})
const logger = pino({ level: 'info' }, stream)

// Nothing is printed
logger.debug('hi')

Usage with Jest

Logging with Jest is problematic, as the test framework requires no asynchronous operation to continue after the test has finished. The following is the only supported way to use this module with Jest:

import pino from 'pino'
import pretty from 'pino-pretty'

test('test pino-pretty', () => {
  const logger = pino(pretty({ sync: true }));
  logger.info('Info');
  logger.error('Error');
});

Handling non-serializable options

Using the new pino v7+ transports not all options are serializable, for example if you want to use messageFormat as a function you will need to wrap pino-pretty in a custom module.

Executing main.js below will log a colorized hello world message using a custom function messageFormat:

// main.js
const pino = require('pino')

const logger = pino({
  transport: {
    target: './pino-pretty-transport',
    options: {
      colorize: true
    }
  },
})

logger.info('world')

// pino-pretty-transport.js
module.exports = opts => require('pino-pretty')({
  ...opts,
  messageFormat: (log, messageKey) => `hello ${log[messageKey]}`
})

Checking color support in TTY

This boolean returns whether the currently used TTY supports colorizing the logs.

import pretty from 'pino-pretty'

if (pretty.isColorSupported) {
  ...
}

Options

The options accepted have keys corresponding to the options described in CLI Arguments:

{
  colorize: colorette.isColorSupported, // --colorize
  colorizeObjects: true, //--colorizeObjects
  crlf: false, // --crlf
  errorLikeObjectKeys: ['err', 'error'], // --errorLikeObjectKeys (not required to match custom errorKey with pino >=8.21.0)
  errorProps: '', // --errorProps
  levelFirst: false, // --levelFirst
  messageKey: 'msg', // --messageKey (not required with pino >=8.21.0)
  levelKey: 'level', // --levelKey
  messageFormat: false, // --messageFormat
  timestampKey: 'time', // --timestampKey
  translateTime: false, // --translateTime
  ignore: 'pid,hostname', // --ignore
  include: 'level,time', // --include
  hideObject: false, // --hideObject
  singleLine: false, // --singleLine
  customColors: 'err:red,info:blue', // --customColors
  customLevels: 'err:99,info:1', // --customLevels (not required with pino >=8.21.0)
  levelLabel: 'levelLabel', // --levelLabel
  minimumLevel: 'info', // --minimumLevel
  useOnlyCustomProps: true, // --useOnlyCustomProps
  // The file or file descriptor (1 is stdout) to write to
  destination: 1,

  // Alternatively, pass a `sonic-boom` instance (allowing more flexibility):
  // destination: new SonicBoom({ dest: 'a/file', mkdir: true })

  // You can also configure some SonicBoom options directly
  sync: false, // by default we write asynchronously
  append: true, // the file is opened with the 'a' flag
  mkdir: true, // create the target destination


  customPrettifiers: {}
}

The colorize default follows colorette.isColorSupported.

The defaults for sync, append, mkdir inherit from SonicBoom(opts).

customPrettifiers option provides the ability to add a custom prettify function for specific log properties. customPrettifiers is an object, where keys are log properties that will be prettified and value is the prettify function itself. For example, if a log line contains a query property, you can specify a prettifier for it:

{
  customPrettifiers: {
    query: prettifyQuery
  }
}
//...
const prettifyQuery = value => {
  // do some prettify magic
}

All prettifiers use this function signature:

['logObjKey']: (output, keyName, logObj, extras) => string

• logObjKey - name of the key of the property in the log object that should have this function applied to it
• output - the value of the property in the log object
• keyName - the name of the property (useful for level and message when levelKey or messageKey is used)
• logObj - the full log object, for context
• extras - an object containing additional data/functions created in the context of this pino-pretty logger or specific to the key (see level prettifying below)
  • All extras objects contain colors which is a Colorette object containing color functions. Colors are enabled based on colorize provided to pino-pretty or colorette.isColorSupported if colorize was not provided.

Additionally, customPrettifiers can be used to format the time, hostname, pid, name, caller and level outputs AS WELL AS any arbitrary key-value that exists on a given log object.

An example usage of customPrettifiers using all parameters from the function signature:

{
  customPrettifiers: {
    // The argument for this function will be the same
    // string that's at the start of the log-line by default:
    time: timestamp => `🕰 ${timestamp}`,

    // The argument for the level-prettifier may vary depending
    // on if the levelKey option is used or not.
    // By default this will be the same numerics as the Pino default:
    level: logLevel => `LEVEL: ${logLevel}`,
    // level provides additional data in `extras`:
    // * label => derived level label string
    // * labelColorized => derived level label string with colorette colors applied based on customColors and whether colors are supported
    level: (logLevel, key, log, { label, labelColorized, colors }) => `LEVEL: ${logLevel} LABEL: ${levelLabel} COLORIZED LABEL: ${labelColorized}`,

    // other prettifiers can be used for the other keys if needed, for example
    hostname: hostname => `MY HOST: ${hostname}`,
    pid: pid => pid,
    name: (name, key, log, { colors }) => `${colors.blue(name)}`,
    caller: (caller, key, log, { colors }) => `${colors.greenBright(caller)}`,
    myCustomLogProp: (value, key, log, { colors }) => `My Prop -> ${colors.bold(value)} <--`
  }
}

messageFormat option allows you to customize the message output. A template string like this can define the format:

{
  messageFormat: '{levelLabel} - {pid} - url:{req.url}'
}

In addition to this, if / end statement blocks can also be specified. Else statements and nested conditions are not supported.

{
  messageFormat: '{levelLabel} - {if pid}{pid} - {end}url:{req.url}'
}

This option can also be defined as a function with this function signature:

{
  messageFormat: (log, messageKey, levelLabel, { colors }) => {
    // do some log message customization
    //
    // `colors` is a Colorette object with colors enabled based on `colorize` option
    return `This is a ${color.red('colorized')}, custom message: ${log[messageKey]}`;
  }
}

Limitations

Because pino-pretty uses stdout redirection, in some cases the command may terminate with an error due to shell limitations.

For example, currently, mingw64 based shells (e.g. Bash as supplied by git for Windows) are affected and terminate the process with a stdout is not a tty error message.

Any PRs are welcomed!

License

MIT License