MCP vs Everything Else: A Practical Decision Guide

Part 4 of 6 – MCP Article Series ← Part 3: How MCP Works: The Complete Request Flow MCP vs Everything Else: A Practical Decision Guide Where MCP fits in the real AI stack — and the one practical decision most developers actually face. MCP gets compared to everything right now — REST, function calling, LangChain, RAG. Most of those comparisons are imprecise. This article explains where MCP actually fits and the one practical decision you will likely face when building with it. Where MCP Sits in the Stack If REST is how services talk to each other, MCP is how AI discovers and uses those services through tools — and they live at different levels of the stack. The bottom two layers already exist in your stack. REST APIs, SQL databases, internal services — none of that changes when you add MCP. What changes is that AI agents now have a standard interface to reach down through the middle tier and use what is already there. An MCP server wrapping a REST API is a normal and correct architectur