REST API: Plain-English Definition + How It Works

A REST API (RESTful API) is a web interface that lets software systems exchange data over HTTP, modeling everything as "resources" addressed by URLs and acted on with standard HTTP verbs (GET, POST, PUT, DELETE). Each request is stateless and self-contained.

What it is

REST stands for Representational State Transfer, a set of design constraints described by Roy Fielding in 2000. An API ("application programming interface") built to follow those constraints is called a REST API or RESTful API. It is the most common way for web and mobile apps, third-party integrations, and backend services to talk to one another.

Why it matters

Because REST builds on plain HTTP, almost every programming language, framework, and tool already supports it with no special libraries. That ubiquity makes REST APIs easy to learn, easy to test (you can hit them from a browser or a simple command-line tool), and easy to cache and scale. When two systems need to share data, REST is usually the default starting point.

How it works: the core principles

Resources and URLs. Everything is modeled as a resource — a user, an order, an invoice — and each resource has a stable URL, such as /users/42 or /orders/1001. You interact with the thing at that address rather than calling a named function.

HTTP verbs map to actions. Instead of inventing custom commands, REST reuses standard HTTP methods: GET reads a resource, POST creates one, PUT or PATCH updates it, and DELETE removes it. The verb says what to do; the URL says what to do it to.

Statelessness. Each request carries everything the server needs to handle it — there is no remembered session between calls. This keeps servers simple to scale horizontally, because any server can handle any request without shared in-memory state.

Standard status codes and formats. Responses use familiar HTTP status codes (200 for success, 404 for not found, 401 for unauthorized) and typically return data as JSON, which is compact and easy for clients to parse.

REST vs GraphQL

REST and GraphQL solve the same problem in different ways. A REST API exposes many fixed endpoints, one per resource, and each returns a predefined shape of data. GraphQL exposes a single endpoint where the client asks for exactly the fields it wants in one query, which reduces over-fetching and under-fetching for deeply nested data. REST stays simpler and is cacheable by default through HTTP; GraphQL shines when many different clients need different slices of the same complex data. Neither is universally "better" — the right choice depends on your data shape, client variety, and team familiarity.

Related terms

Explore neighbouring concepts: GraphQL (a query-based alternative to REST), Microservices (which typically communicate through REST APIs), and the broader Apex IT Solutions Glossary. On the build side, see Application Development and DevOps Solutions.

FAQ

Is REST the same as HTTP?
No. HTTP is the transport protocol; REST is an architectural style that uses HTTP conventions. A REST API relies on HTTP methods and status codes, but you can also build non-REST interfaces (like RPC or GraphQL) on top of HTTP.

What is the difference between REST and GraphQL?
REST exposes many fixed endpoints, one per resource, and you fetch whatever each returns. GraphQL exposes a single endpoint and lets the client request exactly the fields it needs in one query. REST is simpler and cacheable by default; GraphQL reduces over-fetching for complex, nested data.

What makes an API "RESTful"?
An API is RESTful when it organizes data as resources with clear URLs, uses HTTP verbs for actions, keeps each request stateless, and returns standard status codes. Many APIs called REST are only partly RESTful in practice, and that is usually fine.

In short, a REST API is the lingua franca of the modern web — a predictable, HTTP-native contract that lets independent systems read and change each other's data.

At Apex IT Solutions

Apex IT Solutions designs and ships REST (and GraphQL) APIs as part of custom software, web, and mobile builds. Learn more about Application Development, or get a free consultation on the right API approach for your project.