JSON (JavaScript Object Notation) is a lightweight data-interchange format. It is easy for humans to read and write. It is easy for machines to parse and generate. JSON is a text format that is completely language independent but uses conventions that are familiar to programmers of the C-family of languages, including C, C++, C#, Java, JavaScript, Perl, Python, and many others. These properties make JSON an ideal data-interchange language. (see www.json.org)
At the above link you will find Json-parsers for a lot of languages. If you language isn't in that list, you can look for the following solution.
At https://www.chilkatsoft.com/ you can find a FREE to use JSON parser for almost all the languages you can think off. They also provide an active-x version, which can be used in most Windows development environments. Check all the components they have, you can buy them all for a low price. If you only need the JSON functionality, they provide it for FREE. Their products are easy to implement and well documented. There are also a lot of samples for each language.
Now that you have decided which Json parser you will use, you can almost start with the development of your iAPI. To test your own server, I would suggest you install Postman.
If you choose Chilkat to create your JSON, you will find the free Chilkat Online tools a real time saver. There is a tool where you can paste a json in, and it will generate the code to use for the language of your choice. See Create source code from JSON. This way you can copy/paste samples of this manual, and use it to create your own source code!