> If something is Interfacing with an Application, and that something is another Application instead of a human, that means the interaction is happening via an Application Interface
My point is, the applications have been (until recently) predominantly written by humans. API is the interface developers use through the code they write. Just like a UI can be better or worse, so can API: it might be concise, expressive, consistent – or verbose, clunky and completely unpredictable. Just like in UI you don’t want to click through dozens of submenus, in API you don’t want to make a dozen of calls to do something simple. It’s way more similar than you think!
Now where MCP fits in here is a whole other question...
> Just like a UI can be better or worse, so can API: it might be concise, expressive, consistent – or verbose, clunky and completely unpredictable. Just like in UI you don’t want to click through dozens of submenus, in API you don’t want to make a dozen of calls to do something simple.
What you're describing are qualities of an interface, as in a User Interface or an Application Interface. You are right that UIs and APIs are similar, because they are both Interfaces. You are right that a good Interface has certain qualities, whether it's a UI or an API. For example, a GraphQL API tries to address the challenge of, "in API you don’t want to make a dozen of calls to do something simple" by consolidating multiple calls into 1.
That said, API is the interface programs use to interact with an application, UI is the interface humans use to interact with a program. Sometimes you get both: A developer interacts with an IDE or text editor (a user interface), and the IDE or text editor interacts with the underlying layer (an application interface).
What you don't see are humans typing bytes to an MCU server, or any other API. Humans are clicking or typing commands into a program via a UI, the program connects to the MCU server via an API, the MCU server connects to, say, a weather server via an API.
My point is, the applications have been (until recently) predominantly written by humans. API is the interface developers use through the code they write. Just like a UI can be better or worse, so can API: it might be concise, expressive, consistent – or verbose, clunky and completely unpredictable. Just like in UI you don’t want to click through dozens of submenus, in API you don’t want to make a dozen of calls to do something simple. It’s way more similar than you think!
Now where MCP fits in here is a whole other question...