You know I really don’t get it. I must be missing something obvious.

Any “tool protocol” is really just a typed function interface.

For decades, we’ve had dozens (hundreds? thousands?) of different formats/languages to describe those.

Why do we keep making more?

Does it really matter who is calling the function and for which purpose? Does it matter if it’s implemented by a server or a command line executable? Does the data transport protocol matter? Does “model” matter?

  interface HelloSayer {
    /** Says hello **/
    String sayHello();
  }

good job! 3k github stars for you sir!!!

If you were to try to implement what you described, you'd figure out what you missed quickly. Namely, that you have to interface your interface to a text interface.