You can specify complex JSON data types with ALT that is similar to JSON Schema, but then with more powerful validation (i.e. regular expressions over sequences) and with less verbosity.
Specifying and checking configuration data is the primary use case of CUE, but you can also specify data with ALT. Head over to the CUE site to see some more use-cases.
In this example we take an existing JSON Schema example and translate that schema to ALT: