What is a REST API?

REST API: definition and origins

REST is neither a protocol nor a piece of software, but an architectural style. Computer scientist Roy Fielding described it in his doctoral dissertation in 2000. An interface that implements these principles is called a REST API or RESTful API.

The focus is on resources—things like customers, orders, or products. Each resource has its own address (URL), such as /api/customers/42. Because REST builds on HTTP, the familiar web protocol, it can be used with almost any programming language.

How a REST API works

A client sends an HTTP request to a URL and uses the method to specify what should happen. The server responds with the data and a status code that describes the result—such as 200 for “success” or 404 for “not found.”

Statelessness is key: the server remembers nothing about the client between two requests. Every request carries all the information it needs. This makes REST APIs highly scalable, because any request can be answered by any server.

• GET: retrieve data, e.g., a customer list
• POST: create a new record, e.g., an order
• PUT / PATCH: change existing data in full or in part
• DELETE: delete a record

Benefits and limitations of REST

REST APIs are easy to understand, easy to document—for example with the OpenAPI standard—and usable by browsers, apps, and servers alike. Responses can be cached, which reduces load and shortens loading times.

Limitations show up with complex data queries: often several requests are needed, or more data is returned than required. In such cases, GraphQL may be the better choice—and for very fast internal communication between services, gRPC.

• Widely used; many tools and developers know the style
• Clear, readable URLs and standardized HTTP methods
• Easy to cache and to scale horizontally
• Nested data can sometimes require many individual requests

Real-world example: one REST API for app and website

A skilled trades business commissions a customer platform: customers book appointments on the website, and installers see their jobs in an app. Both access the backend through the same REST API. New channels—such as a customer portal—can be connected later without building the business logic twice.

In practice, what counts is clean versioning (e.g., /api/v1/), clear error messages, authentication, and request limits (rate limiting). Nano Concepts designs and develops REST APIs including documentation, so your team or external partners can work with them too.