pretty.md

Pretty Printing

By default, Pino log lines are newline delimited JSON (NDJSON). This is perfect for production usage and long-term storage. It's not so great for development environments. Thus, Pino logs can be prettified by using a Pino prettifier module like pino-pretty:

$ cat app.log | pino-pretty

For almost all situations, this is the recommended way to prettify logs. The programmatic API, described in the next section, is primarily for integration purposes with other CLI-based prettifiers.

Prettifier API

Pino prettifier modules are extra modules that provide a CLI for parsing NDJSON log lines piped via stdin and expose an API that conforms to the Pino metadata streams API.

The API requires modules provide a factory function that returns a prettifier function. This prettifier function must accept either a string of NDJSON or a Pino log object. A pseudo-example of such a prettifier is:

The uninitialized Pino instance is passed as this into prettifier factory function, so it can be accessed via closure by the returned prettifier function.

module.exports = function myPrettifier (options) {
  // `this` is bound to the pino instance
  // Deal with whatever options are supplied.
  return function prettifier (inputData) {
    let logObject
    if (typeof inputData === 'string') {
      logObject = someJsonParser(inputData)
    } else if (isObject(inputData)) {
      logObject = inputData
    }
    if (!logObject) return inputData
    // implement prettification
  }

  function isObject (input) {
    return Object.prototype.toString.apply(input) === '[object Object]'
  }
}

The reference implementation of such a module is the pino-pretty module. To learn more about creating a custom prettifier module, refer to the pino-pretty source code.

Note: if the prettifier returns undefined, instead of a formatted line, nothing will be written to the destination stream.

API Example

NOTE:

For general usage, it is highly recommended that logs are piped into the prettifier instead. Prettified logs are not easily parsed and cannot be easily investigated at a later date.

1. Install a prettifier module as a separate dependency, e.g. npm install pino-pretty.
2. Instantiate the logger with the prettifier option:

const pino = require('pino')
const log = pino({
  prettifier: require('pino-pretty')
})