I'll bite. What other format would you have chosen that's widely supported, easy to read and type by hand, and supports deeply nested data structures?

I mean, defining the service in some sort of universal definition format is clearly the way to go. Working with BLE across platforms is incredibly terse and error-prone. The UUIDs should only be in one file -- human eyes aren't going to notice a single-character mistake in those things.

A far-less-error prone and faster approach I've taken recently is just having two busses -- one read/write characteristic for inbound messages to the peripheral, and one r/w/notifying characteristic for inbound messages to the central. Then all messages just get defined as protocol buffers. Adding new characteristics for new functionality is a massive pain. Easier to just add new protos and use the same pipe.

I started with TOML but switched to YAML because people are familiar with OpenAPI. Ultimately everything is parsed to a Javascript object so you can have adapters in your favourite spec language.