REST API

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The REST API is a widely used set of rules for how programs request and send data to each other over the internet, using the same technique by which web pages load.

In plain terms

Imagine a restaurant counter. You do not enter the kitchen but place your order at the counter in a familiar format and receive what you requested. An API (application programming interface) is such a counter between two programs; REST is the house rule at the counter, meaning how requests must be made and in what format responses arrive.

The essence of REST is simplicity. Every item, such as an order, a customer, or a weather forecast, has its own web address, and a few basic operations can be performed with these: retrieve, create, modify, delete. Since it uses the same web technology as your browser, almost any program and device can communicate this way.

This is why it became the common language of software. When an app shows your bank balance, a courier's location, or tomorrow's weather, it likely requests data via a REST API in the background. AI agents also mostly access external services through such interfaces when booking, searching, or recording data for you.

How it works

The requesting program (the client) compiles a request: it specifies the URL, which identifies the subject, such as a specific order.
It also selects the operation: GET retrieves, POST creates a new one, PUT or PATCH modifies, DELETE removes.
The request usually includes an identifier, known as an API key or token, so the provider knows who is requesting and what rights they have.
The server performs the operation and responds by sending a status code (for example, 200 = OK, 404 = not found) along with the data, most often in JSON format.
The server does store the data, but it does not remember the history of requests: each request must contain everything needed to fulfil it. This makes the system easy to scale, because any server can handle any request.

An everyday example

You open the weather app on your phone, and within seconds the forecast for your city appears. The app sends a request to the meteorological provider's REST API in the background, then presents the received data to you in a nicely formatted way.

Who is affected

developerIt is part of your daily work: you connect most external services and AI models to your own program via REST API. → Code

entrepreneur, executiveIf software has a REST API, you can connect it to your other systems and automate work, so it is worth asking about this before purchasing.

bank customer, investorOpen banking is built on such interfaces: this allows an application you authorize to view your account or initiate payments from it. → Money

everyoneYou use it many times a day without realizing it, because most of your mobile apps get fresh data this way.

A common misconception

MythA REST API is a program or product that can be purchased and installed.

In realityREST is a design style, that is, a collection of rules, which each provider implements on its own interface. Therefore, no two REST APIs are exactly alike, and each has its own separate documentation.

Limits and risks

REST is not a strict standard, so providers interpret it differently: what works on one interface may work differently on another.
An API key is like a password: if it leaks, others can use the service in your name, even at your expense.
Most providers limit how many requests you can send within a given time, and higher traffic often requires payment.
If the provider changes or discontinues its interface, the applications and automations built on top of it may stop working.

Similar, but not the same

API – API is the general term for any interface between programs; REST API is one type of it and the most widespread among web APIs.
GraphQL – With GraphQL, the requester specifies exactly what data they need at a single address with their own query, whereas with REST, every item has a separate address and a fixed response.
MCP (Model Context Protocol) – MCP was designed specifically so that AI agents can discover and use tools in a uniform way, whereas REST APIs are general-purpose, and a REST API is often what does the work behind an MCP server.

Related concepts

Broader

API, web service, Software Architecture

Narrower

endpoint, HTTP method, Status Code

On the edge

JSON, HTTP, API key, GraphQL, MCP

A brief history

The concept of REST was introduced by American computer scientist Roy Fielding in his doctoral dissertation defended in 2000, in which he systematized the basic principles of the functioning of the World Wide Web. The name is an abbreviation of Representational State Transfer.

Where things stand

As of late 2026, REST is the default way to connect web and mobile services, and the major AI models are typically available through such interfaces. As AI agents spread, new protocols tailored to agents are being built on top of it, but they complement REST rather than replace it.

Status: 2026 November

Also known as

REST API · REST · RESTful API · REST-API · REST interface · REST-based API · Representational State Transfer

Sources

This entry was machine-edited and has undergone machine expert review; the “In the news” section updates automatically from Agent Age stories.