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yaml is a JavaScript parser and stringifier for YAML, a human friendly data serialization standard. It supports both parsing and stringifying data using all versions of YAML, along with all common data schemas. As a particularly distinguishing feature, yaml fully supports reading and writing comments and blank lines in YAML documents.

The library is released under the ISC open source license, and the code is available on GitHub. It has no external dependencies and runs on Node.js 6 and later, and in browsers from IE 11 upwards.

For the purposes of versioning, any changes that break any of the endpoints or APIs documented here will be considered semver-major breaking changes. Undocumented library internals may change between minor versions, and previous APIs may be deprecated (but not removed).

For more information, see the project's documentation site:

To install:

npm install yaml@next

Note: These docs are for yaml@2. For v1, see the v1.10.0 tag for the source and for the documentation.

API Overview

The API provided by yaml has three layers, depending on how deep you need to go: Parse & Stringify, Documents, and the CST Parser. The first has the simplest API and "just works", the second gets you all the bells and whistles supported by the library along with a decent AST, and the third is the closest to YAML source, making it fast, raw, and crude.

import YAML from 'yaml'
// or
const YAML = require('yaml')

Parse & Stringify

YAML Documents

import { Pair, YAMLMap, YAMLSeq } from 'yaml/types'

CST Parser

import parseCST from 'yaml/parse-cst'


# file.yml
  - A human-readable data serialization language
  - A complete JavaScript implementation
import fs from 'fs'
import YAML from 'yaml'

// 3.14159

YAML.parse('[ true, false, maybe, null ]\n')
// [ true, false, 'maybe', null ]

const file = fs.readFileSync('./file.yml', 'utf8')
// { YAML:
//   [ 'A human-readable data serialization language',
//     '' ],
//   yaml:
//   [ 'A complete JavaScript implementation',
//     '' ] }


import YAML from 'yaml'

// '3.14159\n'

YAML.stringify([true, false, 'maybe', null])
// `- true
// - false
// - maybe
// - null
// `

YAML.stringify({ number: 3, plain: 'string', block: 'two\nlines\n' })
// `number: 3
// plain: string
// block: |
//   two
//   lines
// `

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