APIs and MCP servers, and how they differ
An API lets any two programs talk. An MCP server is a protocol built for language models. This explainer draws the split, the handshake and when each one is the right choice.
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Transcript
The Fundamental Split
An API is a set of rules that lets one program ask another program for work or data.
An MCP server is a specific type of program that speaks to language models—tools like Claude or GPT.
The split: APIs are general connectors between any two pieces of software. MCP is a protocol built for LLMs.
How APIs Work
Your phone calls a weather API by sending a request to a web address, usually over HTTP.
The API server on the other end looks up the temperature in Denver and sends back a response in JSON format.
This request-and-response cycle can happen between billions of different kinds of software.
What MCP Does Differently
MCP—the Model Context Protocol—is a standard Claude.ai or other LLM products use to call tools.
Instead of a general-purpose request, the LLM asks an MCP server what capabilities it has, then picks one and runs it.
MCP server wraps older APIs or databases so the LLM can use them without breaking its reasoning flow.
The Caller and the Called
With a regular API, any client can call it: a web browser, a mobile app, another server.
With MCP, the client is always a language model. The LLM decides whether and when to use the MCP server.
This shapes the whole conversation: the model stays in charge.
Format and Protocol
APIs speak HTTP, REST, GraphQL, gRPC—dozens of standards built over thirty years.
MCP uses JSON-RPC as its message format, a lightweight protocol that sends function calls back and forth.
Both are text-based and machine-readable, but MCP's design assumes a language model is the reader.
Why the Distinction Matters
If you're building software that talks to other software, you use an API.
If you're giving an LLM new abilities—access to a database, a calendar, a real-time feed—you wrap it in MCP.
MCP is not a replacement for APIs; it's a bridge that lets LLMs safely use them.
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