Json is quite common file type for configuration/storage files, it is rather fast, but fairly hard to read as a human.

Yaml is not as fast as Json but way easier to read, which is why a lot of programs rely on it as their config files (mostly config.yml).

Toml is a compromise between the readybility of Yaml and the performance of Json, thus being a quite good way to go.

ThunderFile is my own implementation of a config file format. It has quite good performance (about as fast as Json) but is way more readable and supports comments.

Yaml and ThunderFile have an additional Config-Version of them implemented with some additional features, like headers and footers.