[Xelynega]

> And because this can now happen at runtime, users (instead of developers) can add arbitrary functionality to applications.

I don't understand what you mean by this. Currently without MCP a server has an API that's documented and to interact with it(thus provide "arbitrary functionality") you call those APIs from your own application code(e.x. python script).

With MCP an LLM connected to your application code calls an API that's documented via MCP to provide "arbitrary functionality".

How are these different, and how does MCP allow me to do anything I couldn't before with API access and documentation? In both cases the application code needs to be modified to account for the new functionality, unless you're also using the LLM to handle the logic which will have very unpredictable results.

[ondrsh]

>In both cases the application code needs to be modified to account for the new functionality, unless you're also using the LLM to handle the logic which will have very unpredictable results.

In the case of MCP, no application code is modified. You first ship the application and then functionality is added. Using plain APIs, it's the other way around. That's the difference.

[Xelynega]

I don't understand this at all.

If my application performs some function dependant on data from an API(e.x. showing tax information, letting a user input tax information, and performing tax calculations and autocomplete), how do I extend that UI easier with MCP than with an HTTP REST API.

Even with MCP I need to update my application code to add UI elements(inputs, outputs) for a user to interact with this new functionality, no?

[ondrsh]

No, MCP does not include any concept of UI (yet). Tool results are usually text only, although there is also the abstraction of an Image (which can be displayed as clients as decide to, e.g. inline).

[Xelynega]

So no application code needs to be changed because no application code exists.

Isn't that like saying you don't need to modify application code with an REST API if your "application" is just a list of instructions on how to use wget/bash to accomplish the task?