Which statement correctly describes the relationship between MCP and vendor function calling?

Attempt it

Quick reference

TL;DR

Function calling is the LLM-to-host layer where the model emits a tool call; MCP is the host to server layer that discovers and exposes those tools. They compose.

Memory aid

Sign in for the mnemonic that makes this stick. See Pro pricing.

Easy to grasp

Picture ordering at a restaurant. Function calling is you telling the waiter, in a clear structured way, 'I want the pasta with no garlic.' MCP is the standardized kitchen-supply system behind the scenes that lets the restaurant source ingredients from any vendor without redesigning the kitchen for each one. You still place your order no matter how the kitchen is stocked. And the supply system works the same whether you order pasta or pizza. They sit at different points in the flow: one is how the model voices a request, the other is how the host reaches out to tools and data. The correct answer is that they are different layers used together, not rivals replacing each other.

Key concepts

Function calling AI agents LLM tool use

Quick scan · 2–4 min

Everything important, quickly.

4 min: name the two layers, eliminate the three replace/superset distractors, then add the three MCP primitives and the JSON-RPC transport.

Side-by-side

Concern	Function calling	MCP
Layer	LLM to host contract	Host to server protocol
Defined by	Each model vendor (OpenAI, Anthropic)	Open spec, vendor-neutral
Transport	Inside prompt and completion	JSON-RPC over stdio or HTTP
Primitives	Tool schemas, tool calls	Tools, resources, prompts
Reusable across apps	No, model-specific shape	Yes, one server runs in any host

Real-world examples

Real products, models, and research that use this idea.

Claude Code ships a built-in MCP client and discovers tools from any registered server at session start, then exposes them to Claude Opus 4.7 as tool_use entries.
Anthropic's MCP server registry exposes filesystem, GitHub, Postgres, and Slack servers as drop-in plug-ins shared across hosts.
Cursor and Zed both adopted MCP so any MCP server written for Claude Code works in them too, while still using each model vendor's own function-calling shape.

Interviewer follow-ups

What an interviewer would ask next. Try answering before peeking at the approach.

QHow would you handle authentication when an MCP server talks to a private API?

Sign in or go Pro to see the approach for this follow-up.

QWhen would you NOT use MCP and prefer direct function calling instead?

Sign in or go Pro to see the approach for this follow-up.

QHow do resources differ from tools, and when does that distinction matter?

Sign in or go Pro to see the approach for this follow-up.

60-second cheat sheet

The night-before-the-interview bullets. Scan these on the way to the call.

Sign in for 5 unlocks/day or go Pro for unlimited revision sheets. See Pro pricing.

References

Primary sources. Skim if you want the original framing.