MCP vs Function Calling: Which Is Better for AI Agents

Tools are an AI agent's window to the real world. Without them, the agent would be restricted to what it already knows.

MCP and Function Calling are both excellent methods of giving an AI Agent access to local or global resources - essential for most useful applications. We need AI to be able to look at our documents, our calendars, our emails; to trawl the web for information, be it stock movements, travel information or news.

Without tools, the LLM would be stuck in the world when it was trained, useful, but not useful enough for real-world applications.

If you’ve been programming AI agents for a while, then you might well turn to function calling to implement a link to an external source.

But isn’t MCP supposed to be the new silver bullet? It seems like the whole world and its dog have implemented an MCP library of tools that lets your agent access their API. So should we follow suit?

To answer that question, we need to ask a few more questions. But first, let’s take a quick look at the two technologies…