What is REST API?

Understanding REST API

REST API is a web interface built around resources, which are items such as users, orders, products, or articles. Each resource has an address, usually a URL. Software interacts with that resource through HTTP methods. For example, GET can retrieve an order, POST can create one, PUT or PATCH can change it, and DELETE can remove it.

Related glossary terms: Application Programming Interface, Backend, HTTP.

REST stands for Representational State Transfer. Roy Fielding described REST as an architectural style based on several constraints. These include a uniform interface, stateless communication, and separation between client and server. A REST API is guided by design principles, rather than one software package or programming language. Many services return JSON because it's readable and supported by most web and mobile development tools.

How REST API Works, Is Measured, or Is Used?

A client sends an HTTP request to an endpoint, which is a URL representing a resource or collection. The request may include a method, headers, query parameters, a body, and authentication details. The server validates the request and performs an operation. It then returns an HTTP status code with a response body when needed.

A typical workflow might request GET /products/42 to retrieve product 42, then send POST /orders to create an order. Status codes communicate the result, such as 200 for a successful response, 201 for a created resource, 400 for invalid input, and 404 when a resource can't be found. Teams assess an API through response time, error rate, throughput, documentation quality, version stability, and security controls.

• GET reads data without changing the resource.
• POST submits data to create a resource or trigger an operation.
• PUT replaces a resource, while PATCH changes selected fields.
• DELETE requests removal of a resource.

Why REST API Matters?

REST APIs allow a website, mobile app, payment service, and internal system to exchange data. They don't need to share the same user interface. This separation lets teams change a frontend while keeping the underlying service available to other clients. Clear resource names, predictable methods, and consistent responses also reduce integration mistakes.

API quality affects reliability, performance, and maintenance cost. Poor validation can corrupt records, weak access controls can expose private data, and unclear error messages can slow development. A well-designed interface documents its request and response formats and applies suitable limits. It also records useful events and manages changes through a clear versioning plan.

When REST API Matters Most?

REST API design becomes important when several applications need the same information or when a project must connect with external services. Common examples include an ecommerce website sharing product data with a mobile app, a booking system sending payment requests, and a content system feeding a public website. The design should identify data ownership and define which clients may read or change each resource.

Security needs close attention when an API handles personal, financial, or business data. Teams should require encrypted connections through TLS and apply authentication and authorization separately. They should validate every input and limit repeated requests. Tests should cover normal, invalid, and unauthorised requests before release. Monitoring should reveal slow endpoints, rising failures, and unusual access patterns.