A linter for YAML files. <code>'''yamllint'''</code> does not only check for syntax validity, but for weirdness like key repetition and cosmetic problems such as lines length, trailing spaces, indentation, etc.
Use an online validator like https://www.yamllint.com/ or https://jsonformatter.org/yaml-validator
Of course, you should have one in your local tools and CI pipeline to ensure that your [[YAML]] is always correct. With the <code>yamllint</code>, there is both a script and a Python module; meaning you can write your own linting tool in Python by invoking (importing) the yamllint module<ref>https://yamllint.readthedocs.io/en/stable/development.html</ref>. See the caveat section below about "using the right tool for the job" - meaning use the right linter for the language/project you are linting. {{Notice|If you have a <tt>.yamllint</tt> file in your working directory, it will be automatically loaded as configuration by yamllint.}}
==Manually fix errors==
Unfortunately, <tt>yamllint</tt> does not fix your file for you. There could be ambiguities about the proper fix, so you need to do the fix(es) yourself.
== Tips Cheatsheet==
You can use '''[https://yamllint.readthedocs.io/en/stable/disable_with_comments.html comment directives]''' to control the behavior of <code>yamllint</code>
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<code>--no-warnings</code> will suppress the warnings so you can focus only on errors.
<code>--list-files</code> will show you the list of files that yamllint finds (and would otherwise lint).
<code>--format</code> (or <code>-f</code>) gives you options for how you want the output to display.
== Yaml multiline ==
Interactive demonstration of Block scalars and Flow scalars https://yaml-multiline.info/
[https://stackoverflow.com/questions/3790454/how-do-i-break-a-string-in-yaml-over-multiple-lines/21699210#21699210 The SO answer that describes them all]
[https://symfony.com/doc/current/reference/formats/yaml.html YAML in Symphony]
[https://docs.ansible.com/ansible/latest/reference_appendices/YAMLSyntax.html YAML in Ansible]
The [https://yaml.org/spec/1.2.2/#scalars YAML 1.2.2 spec on scalars]
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==Many linters==
You can't just use "one" solution either<ref>https://phabricator.wikimedia.org/T95890</ref>. The leading GPL linter is based on Python, so depending on your code repo, you may instead want to use a JavaScript or PHP implementation. Thus, tools like [[wp:Grunt (software)]] may be used to automate JSHint linting in [[JavaScript]] projects<ref>https://www.codereadability.com/jshint-with-grunt/</ref>.