[myownpetard]

MCP is more like a UI that is optimized for LLMs for interacting with a tool or data source. I'd argue that an API is not a user interface and that's not really their intention.

> Regardless, again: if the AI is so smart, and it somehow needs something akin to MCP as input (which seems silly), then we can use the AI to take, as input, the human readable documentation -- which is what we claim these AIs can read and understand -- and just have it output something akin to MCP.

This example is like telling someone who just wants to check their email to build an IMAP client. It's an unnecessary and expensive distraction from whatever goal they are actually trying to accomplish.

As others have said, models are now being trained on MCP interactions. It's analogous to having shared UI/UX patterns across different webapps. The result is we humans don't have to think as hard to understand how to use a new tool because of the familiar visual and interaction patterns. As the design book title says, 'don't make me think.'

[notpushkin]

> I'd argue that an API is not a user interface and that's not really their intention.

API is a user interface for other developers – just like MCP is a UI for LLMs.

[ImPostingOnHN]

The U in UI is User, and refers to the human. 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 (to make things easier, we'll call it an AI for short...just kidding).

That seems to be what happens here with MCP: it is a way for an Application (the LLM) to derive programming by Interfacing with another Application (the 3rd party API provider, for example).

That would make MCP an API for accessing other APIs. Not that that's bad, computers are layers of abstraction all the way down. At the same time though, we already have some of those. Perhaps some sort of OpenAPI bridge would be useful in the same manner and not require rewriting API specs, but that probably exists, too.

Who am I kidding, though? The AI assistants/agents are going to be writing whatever manifests are necessary to run more AI, so it'll be a negligible increase in effort to do both.

[notpushkin]

> 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...

[ImPostingOnHN]

> 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.