Guides

MCP vs API: what's the difference?

An API is how one program talks to another, and a developer writes the code that calls it. MCP is a standard way to offer tools to AI agents, which discover the tools and decide when to call them while they work. Many MCP servers are built on top of an API, so a business often offers both.

By Vadim DunaevskiyUpdated October 21, 2026Sources checked October 15, 20264 min read

The difference at a glance

	API	MCP server
Who calls it	Code a developer wrote	An AI agent, while it works
How the caller learns what exists	Documentation, often an OpenAPI file	A `tools/list` request; each tool describes its inputs in JSON Schema²
Message format	Usually HTTP requests with JSON	JSON-RPC 2.0, over Streamable HTTP or a local process^1,5
Sign-in	API keys or OAuth, set up per vendor	OAuth 2.1 with standard discovery for remote servers,³ or a key in a header
Who decides which call to make	The developer, ahead of time	The model, from your request, with a person able to deny a call²

How an API works

An API lists the requests a program can make: create an invoice, look up a customer, cancel an order. Many companies describe theirs with the OpenAPI Specification, which the OpenAPI Initiative calls "a specification language for HTTP APIs", written in YAML or JSON.⁴ A developer reads that description, writes code that calls the right endpoints in the right order, and ships it. The developer fixes the calls when writing the code, and changing them takes a new release.

How MCP works

An MCP server offers tools, each with a name, a description of what it does and a JSON Schema for its inputs.² The AI app, such as Claude or ChatGPT, connects to the server, asks for the list of tools, and lets the model pick one when a request calls for it.¹ The specification calls tools model-controlled, meaning the model finds and calls them based on the conversation and your request.²

Because the model chooses, the specification asks for a check. It says there should always be a human in the loop with the ability to deny a tool call, and that apps should make clear which tools the model can use.² For a full walk through hosts, clients and servers, see what an MCP server is.

How they fit together

Many MCP servers call an API underneath, and Stripe's is a clear example. Its tools search Stripe's API methods by keyword, read with any GET method and write with any POST, PATCH, PUT or DELETE method.⁶ The MCP layer adds what an agent needs on top: tools it can find without reading documentation, inputs it can fill without custom code, and a standard way to sign in.

Conecto, our product, offers every tool both ways. Each one is a REST endpoint, POST https://api.conecto.chat/v1/tools/<name>, and the same tool is on Conecto's MCP server at https://api.conecto.chat/v1/mcp, and on its area's own server at https://api.conecto.chat/mcp/<area>.¹⁰ There are OpenAPI files too, for custom GPT actions and Microsoft Copilot Studio.¹⁰ The price, the log and the daily budget are the same whichever way a call arrives.

When to use which

Use the API when you write the code and know the steps in advance: a nightly sync, a form on your website that saves a lead, a report that runs every Monday.
Use MCP when a person asks an agent for something and the agent should work out the steps, such as "Send Hansen & Voss the October invoice and remind them it's due on the 28th."
Use both as a habit. Let the agent handle new requests through MCP, and when a task settles into the same steps every time, move it to code that calls the API.

Costs and limits

Code that calls an API uses no room in a model's context, because no model chooses the calls. An MCP tool's name, description and input schema go into the model's context so it can choose, which adds up when an agent connects many servers. Anthropic launched Tool Search in its API to help production deployments handle thousands of tools,⁹ and connecting only the servers a task needs keeps the list short.

Vendors can price the two paths differently. Zapier counts each MCP tool call as two tasks from your plan,⁷ and a standard action in a Zap as one.⁸ On Conecto, a call costs the same through REST or MCP. Reading your own data is free up to a million reads a month, and a change to a record costs $0.01.¹⁰

Questions

Is MCP replacing APIs?

No. Many MCP servers call an API underneath, so the API stays. MCP adds a standard way for agents to find and use what an API can do.

Can I turn my API into an MCP server?

Yes. Wrap the endpoints you want an agent to use as tools, each with a clear name, a description and a JSON Schema for its inputs, using one of the official MCP SDKs.⁹ Write the descriptions for a model that has never seen your documentation.

Is MCP more secure than an API?

The access underneath is the same. MCP adds a standard sign-in for remote servers, built on OAuth 2.1,³ and asks apps to let a person deny each call.² Because a model chooses the calls, text in a web page or an email can try to steer it, which is called prompt injection. Stripe's documentation asks you to turn on your client's tool approval and to watch for prompt injection when its server runs beside others.⁶ Keep tools that send, pay or delete behind your approval.

Does ChatGPT use MCP or APIs?

Both. You add a remote MCP server in ChatGPT as a custom MCP server,¹¹ and servers that take actions need a Business, Enterprise or Edu plan.¹³ Custom GPTs call APIs described in OpenAPI files through actions,¹² but OpenAI retires custom GPTs on December 11, 2026, and their actions have to be rebuilt, for example as a custom MCP server.¹⁴

Sources

We read these pages on October 15, 2026. Each number in the guide links to the page behind that sentence.

Conecto publishes this guide and sells business tools for AI agents. How we write our guides. To report a mistake, write to hello@conecto.chat.

Written by Vadim Dunaevskiy, Co-founder of Conecto. LinkedIn