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2.2.0 • Public • Published


Validate Yaml files and enforce a given structure

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Yaml files are parsed via js-yaml and the structure defined in the configuration options is enforced with check-type.

Getting Started

Please note that the minimum supported version of Node.js is 8.11.1, which is the active Long Term Support (LTS) version.

This tool can be used in two ways, either via Node.js script, or as a command line tool. Note that when used via command line, custom structure cannot be validated.

Installation when used via Node.js script:

npm install yaml-validator --save-dev

Installation when used as a command line tool:

npm install --global yaml-validator

Usage as a part of a Node.js script:

const YamlValidator = require('yaml-validator');
// Default options
const options = {
  log: false,
  structure: false,
  onWarning: null,
  writeJson: false
const files = [
  'file paths',
  'that exists',
  'and are Yaml files'
const validator = new YamlValidator(options);

Using via command line tool, the only argument would be the Yaml file which should be validated:

yaml-validator random_file.yml

The available options for command line use, can be seen with the help command yaml-validator -h, which results in output similar to:

yaml-validator [options] <files>
  -h, --help             Help and usage instructions
  -V, --version          Version number
  -w, --write-json       Write the contents of the Yaml file to a JSON file next to it
  -l, --log-file String  Log file where errors are written
Version 2.0.0

When used from the command line, the process exits with the number of invalid files.

Configuration options

All options are false by default which disables their use.


Type: string

Default value: false

In case the value is not false, the given string will be used as log file where all the task output is written.


Type: object

Default value: false

The most complex style of checking validity.


Type: function

Default value: null

One of the options passed to safeload method of js-yaml.

Please note that the onWarning callback is being used by this library and any method written for it, will be run after the one implemented in this library. The callback get called with two parameters, of which the first is the error in question, while the second is the file path of the given Yaml file.


Type: boolean

Default: false

Write the given Yaml file as pretty printed JSON in the same path, just by changing the file extension to json.

Please note that any existing JSON files will be cruelly overwritten.

Typescript Support

YamlValidator ships with its own typing definition in the library, no need to use @types.


Structure validation options

In case an array is found, all its members are assumed to have the given structure. This can be seen in the classRooms property, which according to the configuration below, should be an array, for which all items are objects, which all should have a name and id properties, with the given types.

The teachers array is made of strings, thus all items in that array must be a string.

const options = {
  structure: {
    school: {
      'description?': 'string', //Optional, won't show in invalid array
      code: 'number',
      principal: {
        name: 'string'
      classRooms: [
          name: 'string',
          id: 'number',
            floor: "string",
            building: "string",
      teachers: [

Warning callback in Yaml parsing options

Using the options.onWarning callback, the possible parsing errors can be retrieved.

const options = {
  onWarning: function (error, filepath) {
    console.log(filepath + ' has error: ' + error);

Write a JSON file option

It is possible to use the options.writeJson to have all the files processed, to be saved in JSON format, in the same file path as the original Yaml files.

const options = {
  writeJson: true


"A Beginner's Guide to Open Source: The Best Advice for Making your First Contribution".

Also there is a blog post about "45 Github Issues Dos and Don’ts".

Linting is done with ESLint and can be executed with npm run lint. There should be no errors appearing after any JavaScript file changes.

Please note that any features or changed will not be merged without working unit tests.

Unit tests are written with tape and can be executed with npm test. Code coverage is inspected with nyc and can be executed with npm run coverage after running npm test. Please make sure it is over 90% at all times.

Release History

  • v2.2.0 (2019-05-29)
    • Internally written as ES2015 Class, instead of ES5 way which polluted prototype
    • Allows now more than just one input file via command line
  • v2.1.0 (2019-04-27)
    • Use npm-shrinkwrap.json for locking the working set of 3rd party dependencies
    • Define files property in package.json to minify files in the published package
  • v2.0.0 (2019-01-17)
    • Minimum supported and tested Node.js version is now v8.11.1
    • The command line tool now exists with the number of failed files, previously always exiting with zero (0) #21
  • v1.3.0 (2018-03-16)
    • Contents of the Yaml file were overwritten, in the case when saving to JSON and the Yaml file suffix was not .yml #14
    • TypeScript types are available #13
    • Dependencies up to 🎩
  • v1.2.0 (2018-01-17)
    • Separated parsing method from file reading method, hence one method more available to use
  • v1.1.0 (2018-01-15)
    • Providing a command line version
  • v1.0.0 (2017-07-13)
    • Time to go major
    • Optional keys are now possible #9
  • v0.4.0 (2017-06-28)
    • Provide file name, error message and line number when failing #7
    • Keep dependencies up to date and test against Node.js major version 8
    • Minimum supported Node.js version lifted from 4.2.0 to 6.9.5
  • v0.3.0 (2016-10-10)
    • Proper unit tests #6
    • options.yaml.onWarning is now options.onWarning
  • v0.2.1 (2016-08-25)
    • Define the minimum Node.js version in package.json, as 4.2.0
  • v0.2.0 (2016-07-06)
    • Using shared ESLint configuration #2
    • Possible JSON file written now replaces extension properly
  • v0.1.0 (2016-02-22)


Copyright (c) Juga Paazmaya

Licensed under the MIT license.




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