The primary problem with YAML is that it allows writing strings without quotes. This causes confusion because it’s impossible to see, from just reading the YAML

The primary problem with YAML is that it allows writing strings without quotes. This causes confusion because it’s impossible to see, from just reading the YAML file, which strings become strings and which are interpreted as numbers or booleans. For example, the identifier blah is interpreted as a string; but 01 is interpreted as a number, which makes it equivalent to 1. Similarly the identifier nope is a string while no is the Boolean literal false, and there’s no clear indicator that the former is a string while the latter is a Boolean.