People make MCP sound more complicated than it is. A SDK and a MCP server both wrap functionality that an API already exposes.
A SDK is a library for one programming language, usually published by the company that owns the API. You import it, call a function, and the library handles the HTTP request.
A MCP server does the same job for a model. The Model Context Protocol is a JSON-RPC specification that anyone can implement. The agent calls a tool, the server receives the request, and an adapter turns it into a REST call against the real API.
The protocol adds discovery and tool schemas, yet the underlying mechanism is still calling the api.
Both are wrappers, and anyone can build either one.
An SDK wraps an API for your code and an MCP wraps an API for a model.