Wrap-up
MCP vs plain function calling
They aren't competitors. They sit at different layers: function calling is how a model asks for a tool, and MCP is how an app finds and runs tools.
function callingMCP
LLM
Host app
MCP server A
MCP server B
MCP server C
| Plain function calling | MCP server | |
|---|---|---|
| Tool lives in | Your app's code | A separate, reusable process or service |
| Reused by | One app | Any MCP-capable host: IDEs, assistants, agents |
| Discovery | Hard-coded | tools/list at runtime, with change notifications |
| Pick it when | A few tools, tightly bound to one product | Many tools, many consumers, or you're publishing an integration |