What is the Model Context Protocol (MCP) and what problem does it solve?

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Quick reference

TL;DR

MCP is an open JSON-RPC protocol that lets any LLM host plug into any tool, data, or prompt server without writing custom integration code per vendor.

Memory aid

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Easy to grasp

Imagine if every electronic device had its own special charger shape, your phone, your laptop, your headphones, all different plugs. That's what LLM app development was like before MCP. Every chatbot had to write custom code to connect to every tool: one wrapper for the database, another for GitHub, another for your file system. MCP is the USB-C of LLM tooling. Anyone can build an MCP server for a service, and any compliant host, Claude Code, Cursor, Zed, can plug it in. The server says, 'here are my tools, here is my data, here are my prompts,' and the host wires those into the LLM. One protocol, many servers, many hosts.

Key concepts

Tool use AI agents Function calling

Detailed answer & concept explanation

~4 min read

Everything you need to truly understand this topic: intuition, mechanics, step by step explanation, code, formulas, and worked example. Click to expand.

Everything you need to truly understand this topic: intuition, mechanics, step by step explanation, code, formulas, and worked example.

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Quick scan · 2–4 min

Everything important, quickly.

3 min: three primitives + two transports + discovery flow + how MCP composes with function calling + which hosts shipped clients.

Real-world examples

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

Claude Code uses MCP to load filesystem, GitHub, and shell tools, all servers Anthropic ships in the public registry.
Cursor and Zed both added MCP clients in 2025 so any Claude-Code-compatible server works in their editors.
Anthropic's MCP server registry catalogs community servers for Postgres, Slack, browser automation, and Notion.

Interviewer follow-ups

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

QHow does an MCP host handle servers it doesn't fully trust?

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QWhat changes when the server is remote instead of local?

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QHow would you eval whether your MCP integration actually helps the model?

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Don't say this

Red flags and common mistakes that signal junior thinking. Click to expand.

Most common mistake

Confusing MCP with function calling. Function calling is the model's tool-output shape; MCP is the host to server transport protocol.

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60-second cheat sheet

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

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References

Primary sources. Skim if you want the original framing.