What is an API and what is it used for in an application?

Published on 2026-10-17 by frfrand

Qué es una API, cómo se comunican frontend y backend, ejemplos cotidianos y diferencias entre una API y una página web.

You open a weather app and see that it will rain tomorrow. Your phone doesn’t have a weather station in every city. At some point, it requested that information from another service. An API defines how a program can request data or functions from another.

API stands for Application Programming Interface, or application programming interface. It sounds much more complicated than it is.

The restaurant explanation

Think of a restaurant menu. You don’t need to know how the kitchen is organized to order a dish. The menu shows what you can request, and the staff handles delivering the order and bringing the result.

An API works similarly: it offers known operations. An application requests information or an action and receives a response according to the defined rules.

The comparison has a limit: an API is not always a server on the Internet. Your browser, your operating system, and many programming libraries also offer internal APIs. But web APIs are especially easy to recognize because they connect programs over the network.

A real example: the online store

Imagine a store with a catalog, cart, and orders. The browser displays buttons and images, but someone needs to store information.

When a person clicks “view products,” the frontend can call a backend API. The backend queries the database and returns the results. When someone confirms a purchase, the frontend requests another operation, and the backend checks availability, permissions, and payment conditions.

The frontend should not freely connect to the entire database with an admin password. A well-designed API helps control which operations are allowed.

What is sent in a request?

In a web API based on HTTP, it is common to find:

• An address: for example, /api/productos.
• A method: GET to query, POST to create or send data, among others.
• Additional data: filters, identifiers, or a JSON payload.
• A response: information or a status indicating what happened.

For example, a response could be:

{
  "producto": "Teclado",
  "precio": 35,
  "disponible": true
}

That is JSON: a way to represent data that two programs can exchange. It is not a visually appealing page, because the goal is for another application to interpret it.

Are API, REST, and webhook the same?

No. API is the general concept. REST describes a frequent design style for web APIs. Webhook is a mechanism by which one system notifies another when an event occurs.

An API can let you query orders whenever you want. A webhook could notify you just when a new one appears. Both can coexist.

Are all APIs public?

Not at all. Some are internal to a company, others are intended for partners, and others allow limited public access. An API may require identification, permissions, request limits, and security checks.

Just because an endpoint exists does not mean anyone has permission to execute it. This detail is fundamental when the API manages customers, payments, or infrastructure.

Where does this appear in ArduMaker?

ArduMaker uses interfaces to communicate components of its platform and offers tools that allow operating certain services from integrations. Understanding an API helps to also understand why an AI agent needs permissions and defined actions to interact with a real system.

In one sentence: an API is an agreement on how two parts of software can communicate. You don't need to memorize all HTTP methods to understand its usefulness, but you do need to know what data is exchanged and who is authorized.

To expand: Introduction to APIs from MDN.