alt Hacker NewsYou're starting too recent though. MCP is attempting to recreate the good parts of REST APIs circa 25 years ago.
Soap was a pain and a lot of people didn't like XML, but they solved exactly these problems.
With MCP we're effectively trying to bolt those features onto a platform that fundamentally doesn't support it. Where as with XML/XSLT we could have a single XML endpoint + XSLT templates for converting that into HTML for browsers. Instead we now have modern web frameworks building RPC calls right into the bundle/build step, splitting state and rendering across both client and server, and have to stand up a new API context for agents that needs documentation and maintenance to keep parity with new features.
This isn't a problem that existed 25 years ago. You could expose SOAP and give an agent WSDL. You could give it OpenAPI and JSON. That's just not the problem.
Agents emit tool calls as JSON. Calling a REST API means emitting a JSON tool call that invokes a HTTP client with all the desirable properties (schema checking, safe auth) and none of the undesirable ones (raw key handling, arbitrary endpoint access). Then the response gets wrapped in JSON and returned to the LLM. That's not an MCP thing, that's a model thing.
MCP says "instead of http_post with a bunch of arguments that need to be correct, call get_weather with a zip code". And then it makes principled choices for how get_weather and its schema is defined. That's literally the whole point.
Even if you wanted to use WSDL to accomplish this, you either have to unwind how literally every function calling implementation of every model works today and teach them how to read WSDL and speak XML (and deal with all the other problems, like auth), or you avoid the two layers of indirection and define a system that works with what exists today, and that solution ends up looking very MCP-shaped.
You might say "well you could just have a little script/xslt that does the translation". That's exactly what a local MCP server is.