This choice in TOML is a mixed bag. I would say it's substantially mitigated by the fact that strings must be quoted, so you don't have strings magically turnin

This choice in TOML is a mixed bag. I would say it's substantially mitigated by the fact that strings must be quoted, so you don't have strings magically turning into datetimes if they look like a date. But it does add substantially complexity to an otherwise simple language. The near-compatibility of ISO 8601 and RFC 3339 is a rich source of bugs, but that's hardly TOML's fault, and the standard is perfectly clear that the latter is used. TOML, like many configuration and data transport languages, is defined in terms of its syntax, so an abstract Date type doesn't make sense for it. Providing a datetime format for TOML was probably the right decision, I think there are more people who complain about JSON lacking one than there are who complain about TOML having one.