I can specify and use tools with an LLM without MCP, so why do I need MCP?

Depends a bit on where your agent runs and how/if you built it.

I'm not arguing if one or the other is better but I think the distinction is the following:

If an agent understands MCP, you can just give it the MCP server: It will get the instructions from there.

Tool-Calling happens at the level of calling an LLM with a prompt. You need to include the tool into the call before that.

So you have two extremes:

- You build your own agent (or LLM-based workflow, depending on what you want to call it) and you know what tools to use at each step and build the tool definitions into your workflow code.

- You have a generic agent (most likely a loop with some built-in-tools) that can also work with MCP and you just give it a list of servers. It will get the definitions at time of execution.

This also gives MCP maintainers/providers the ability/power/(or attack surface) to alter the capabilities without you.

Of course you could also imagine some middle ground solution (TCDCP - tool calling definition context protocol, lol) that serves as a plugin-system more at the tool-calling level.

But I think MCP has some use cases. Depending on your development budget it might make sense to use tool-calling.

I think one general development pattern could be:

- Start with an expensive generic agent that gets MCP access.

- Later (if you're a big company) streamline this into specific tool-calling workflows with probably task-specific fine-tuning to reduce cost and increase control (Later = more knowledge about your use case)