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    4.0.0 • 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 14.15.0, 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 load 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.

    Version History

    Changes happening across different versions and upcoming changes are tracked in the CHANGELOG.md file.


    Copyright (c) Juga Paazmaya paazmaya@yahoo.com

    Licensed under the MIT license.




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