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Comment by totaldude87 | Hacker News Reader

isnt langchain doing the exact same thing? (sorry ai noob here)

Langchain is one of many frameworks that implement the "tool calling" pattern, where LLM applications can request that a tool is run (eg "search the web for X" or "execute this Python code") and see the result of that.

MCP is a standard for describing and exposing tools to LLM applications.

So they're not the same category of thing. Langchain could implement aspects of the MCP specification, in fact it looks like they're doing that already: https://github.com/langchain-ai/langchain-mcp-adapters

So, is MCP a spec for tool calling API?

There's a MCP "server" spec for writing code that exposes tool definitions and the ability to execute them, and an MCP "client" spec for building systems that can make use of those servers.

it's more than just tools. there're prompts & resources too

It's a spec for how external info can get into a language model's context window. Part of that is tool calling, but there's also templated input, cancellation, progress tracking, recursive generation sampling, statefulness of tool servers, etc.

It's a common question!

Related: > Tool-Calling - If you’re like me, when you first saw MCP you were wondering “isn’t that just tool-calling?”...

Not everyone uses langchain nor does langchain cover some of the lower level aspects of actually connecting things up. MCP just helps standardize some of those details so any assistant/integration combo is compatible.

Edit: +1 simonw above

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