A linter for YAML files. yamllint 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 yamllint, 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[1]. 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.
 | If you have a .yamllint file in your working directory, it will be automatically loaded as configuration by yamllint. |
Contents
Manually fix errors
Unfortunately, yamllint does not fix your file for you. There could be ambiguities about the proper fix, so you need to do the fix(es) yourself.
Cheatsheet
You can use comment directives to control the behavior of yamllint
With disable-line you put the directive in-line, or on the line above.
# The following mapping contains the same key twice,
# but I know what I'm doing:
key: value 1
# yamllint disable-line rule:key-duplicates
key: value 2
# yamllint disable-line rule:line-length
- This line is waaaaaaaaaay too long but yamllint will not report anything about it.
This line will be checked by yamllint.
With disable you can disable multiple rules for the entire file.
# yamllint disable rule:hyphens rule:commas rule:indentation
Or even use disable-file
# yamllint disable-file
# This file is not valid YAML because it is a Jinja template
--no-warnings will suppress the warnings so you can focus only on errors.
--list-files will show you the list of files that yamllint finds (and would otherwise lint).
--format (or -f) 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/
The SO answer that describes them all
The YAML 1.2.2 spec on scalars
Many linters
You can't just use "one" solution either[2]. 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[3].
Source, Docs and Reading
- https://github.com/adrienverge/yamllint
- https://yamllint.readthedocs.io/en/stable/
- https://www.redhat.com/sysadmin/check-yaml-yamllint