YAGNI works well as long as you are willing to re-write your code in the rare cases when you do "need it".
It's fine to start without a real parser, and you often will end up not ever needing a real one, but if the complexity of your ad hoc solution starts getting anywhere close to the complexity of a real parser, you are better off re-writing it as a real parser because parsing is an extremely well-studied area of CS while your ad-hoc "not parsing" is not.
It's fine to start without a real parser, and you often will end up not ever needing a real one, but if the complexity of your ad hoc solution starts getting anywhere close to the complexity of a real parser, you are better off re-writing it as a real parser because parsing is an extremely well-studied area of CS while your ad-hoc "not parsing" is not.