Why are they not calling APIs directly with strictly defined inputs and outputs like every other internal application?

The story for MCP just makes no sense, especially in an enterprise.

MCP is an API with strictly defined inputs and outputs.

This is obviously not what it is. If I give you APIGW would you be able to implement an MCP server with full functionality without a large amount of middleware?

If I gave you that could you implement Graphql from scratch without a large amount of middleware? Or are we now saying graphql api:s are not api:s?

Sorry, could you rephrase that?

I’ve implemented an MCP tool calling client for my application, alongside OAuth for it. It was hard but no harder than anything else similar. I implemented a client for interference with the OpenAI API spec for general inference providers, and it was similarly as hard. MCP. SDKs help make it easy; MCP servers are dead simple. Clients are the hard part, IMO.

MCP is basically just an RPC API that uses HTTP and JSON, with some other features useful for AI agents today.

Does MCP support authentication, SSO?

It supports OAuth, IIRC. But I suppose the internal chatbot itself would require auth, and pass that down to the tools it calls.

The chatbot app initiates an OAuth flow, user SSOs, chatbot app receives tokens to its callback URL, then tool calls can access whatever the user can access.

If you use the official MCP SDK, it has interfaces you implement for auth, so all you need to do is kick off the OAuth flow with a URL it figures out and hands you, storing the resulting tokens and producing them when requested. It also handles using refresh tokens, so there's just a bit of light friendly owl finishing on top.

Source: I just implemented this for our (F100) internal provider and model agnostic chat app. People can't seem to see past the coding agents they're running on their own machines when MCP comes up.

Neat!

Yes it’s literally just standard OAuth that’s defined in the MCP spec. I spent this week implementing an auth layer for my app’s MCP client gateway.

MCP really only makes sense for chatbots that don’t want to have per session runtime environments. In that context, MCP makes perfect sense. It’s just an adapter between an LLM and an API. If you have access to an execution engine, then yes CLI + skills is superior.

Only is doing a lot of work here. There are tons of use cases aside from local coding assistants, e.g., non-code related domain specific agentic systems; these don’t even necessarily have to be chatbots.

OP's point is about per session sandboxes, not them necessarily being "chatbots". But if you don't burry the agent into a fresh sandbox for every session you have bigger problems to worry about than MCP vs CLI anyway

actually local MCP just spawns a subprocess and talks via stdin/stdout.. same as CLI tool. Extra layer is only for remote case.

This might help if interested - https://vectree.io/c/implementation-details-of-stdio-and-sse...

> and you probably don't want to run a CLI in a sandbox somewhere for every session

You absolutely DO want to run everything related to LLMs in a sandbox, that's basic hygiene

You're missing their point, they're saying that you'd need a sandbox -> it'd be a pain -> you don't want to run a CLI _at all_