It is not realistic to manually create JSON schema. It is something used by the system, there are aspects which are difficult to understand how to write, and it is bothersome to describe things such as the validation conditions.
This is why JSON schema generation software and libraries are so useful. They are available for all types of programming languages, making it easy to choose the one that suits you.
The Python library defines, for all items, the type and whether or not input is required. Rather than using the generated result as-is it appears that it would be better to use it after compiling the value range and whether or not items are required.
This is a JSON schema generator which uses Jackson (a Java JSON library). Specify the Java object and then convert that property into JSON schema. This could be used when you want to change a system which is actually operating to a JSON schema.
This is available as software for Windows. The JSON can be defined visually and validation can be specified in fine detail. This appears to be very usable, with features includes drag-and-drop structure editing.
This is a library that can convert Go objects to JSON schema. All properties can be defined and required conditions can be described. It is necessary to describe validation separately.
There seem to be two methods of generating JSON schema – one which outputs objects in various programming languages as JSON schema and one which visually creates JSON schema.
It appears that libraries can be used even with systems that are already running. Note, however, that you will need to have detailed validation settings. The visual editors could be used right from when thinking about specifications.