Complete API – or Guide – or Manual ?

Hello,

I would like to add some buttons, and some funsctions – probably using an addon or simply inside the skin.
Simple things I did with visualstudio (microsoft) years ago.

I cannot find any Kodi complete API guide, or manual to help me.
I can find samples, general help, how to start guides. That’s all.

I’m a new Kodi user (I started less than 15 days ago) and believe this software is worth developing / using.
So many posts here, reading – and understanding all of them would take years.

Kodi is using specific terms, functions, and if you do not know they exist, you cannot do anything.

Why no complete help ?
Is it because you use python, and python has an API ?
AND
because json-rpc has it’s own API ?

Or is it simply because I do not know where to search.

Thanks for all the work developers did with Kodi . I know it’s time consuming and often ” du travail mal reconnu”.