Explainer1 min readUpdated July 7, 2026

What is a REST API?

Short answer

A REST API is a way for programs to exchange data over HTTP. Each thing is a resource with a URL, you act on it with HTTP methods like GET, POST, PUT, PATCH, DELETE, and sometimes QUERY, and the server replies with data and a status code. Each request stands on its own.

Resources and URLs

In REST, everything is a resource addressed by a URL. /users is the collection of users; /users/42 is one specific user. You interact with these URLs rather than calling named functions.

Methods describe the action

GET reads a resource without changing it
QUERY runs a safe, idempotent query with request content when the API supports it
POST creates a new resource
PUT or PATCH updates an existing resource
DELETE removes a resource

GET /users/42  ->  200 OK
{ "id": 42, "name": "Ada" }

A request and its response

One request, one response

GET /users/42request

Server

200 OK + JSONresponse

Requests are statelessEach request carries everything the server needs, including authentication. The server does not remember previous calls, which makes REST APIs easy to scale.

Try it: REST Request TesterBuild and send REST requests, then inspect the response, locally in your browser.Open tool

Status codes tell you what happened

The response includes an HTTP status code: 2xx for success, 4xx when the request was wrong, and 5xx when the server failed. See HTTP status codes for the full list.

References

Questions

What is the difference between PUT and PATCH?

PUT typically replaces a whole resource, while PATCH applies a partial update to specific fields. Which one an API expects depends on its design.

Is REST the same as JSON?

No. REST is an architectural style; JSON is just the most common format REST APIs use for request and response bodies. A REST API could use other formats.

Does REST use the new QUERY method?

Some APIs may adopt QUERY for complex read-only searches after RFC 10008 standardized it in 2026. It is safe and idempotent like GET but can carry request content. Most existing APIs still use GET or POST until their servers and clients support QUERY.

Does this send my data anywhere?

No. Utilumo's developer tools parse and transform input inside the browser tab. Nothing is uploaded, stored, or logged.