It's not made explicit in the documentation, but TOML is very nearly a superset of JSON - just using `=` to separate key-value pairs instead of `:`, and requiring top-level names to be given explicitly, and requiring the "inline" bits to be on a single line. In TOML, your example can equivalently be:

    a = { b = [ { x = 1 } ], y = 2 }

(And yes, that can be the entire document; you can have an inline table before the first table header.)

Of course, this doesn't help if you want the top level to be an "array" rather than an "object" (in JSON parlance), or if you want the entire document to represent a single primitive value. But these uses are discouraged at best anyway.

But really the goal of TOML is to highlight the location of important parts of the deserialized tree structure (hence the ability to use arbitrary long dotted paths in table headers) rather than the structure itself. It's IMO a beautiful implementation of the idea "flat is better than nested" from the Zen of Python, and it neatly sidesteps an issue I asked about many years ago on Stack Overflow (https://stackoverflow.com/questions/4372229 - the question was rightfully closed, as this sort of discussion doesn't fit the Q&A format; but it made sense to ask at the time).

I don't know if a direct comparison of TOML to YAML is fair. Among other differences, the standard way to parse YAML in Python involves a third-party library that brings in a ~2.5 MB compiled C library. Every TOML implementation I encountered - including the one that made it into the standard library - is pure Python.