[davebranton]

YAML is much too complex. I am never able to remember all the different ways of formatting text, for instance, and have to resort to cheat-sheet guides such as this all the time.

https://yaml-multiline.info/

The YAML spec is thousands of lines long (23k words, to be more exact). This is even longer than XML (20k words). JSON's spec is less than two thousand words. For a language that's supposed to be human-readable, YAML is maddeningly complex.

https://yaml.org/spec/1.2.2/

Plus, of course, you can execute arbitrary code with it. By design. AND it contains semantic whitespace, which is personally my least favourite innovation ever.