RESTful APIs (Representational State Transfer APIs) are a standardized way for systems to communicate over the web using HTTP protocols. They are designed around resources—such as users, products, or data entries—that are accessed and manipulated through URLs. Each resource is represented by a unique URI, and operations on these resources are performed using standard HTTP methods like GET (retrieve), POST (create), PUT (update), and DELETE (remove). This architectural style promotes simplicity, scalability, and statelessness, meaning each request is independent and contains all the necessary information.

One of the most common formats used in RESTful API communication is JSON (JavaScript Object Notation). JSON is lightweight, easy to read, and widely supported across programming languages, making it ideal for transmitting structured data between clients and servers. When a client sends a request to a RESTful API, it typically includes JSON-formatted data in the body (for POST or PUT), and the server responds with JSON that represents the requested resource or the result of the operation. This format allows for clear, structured exchanges that are both human-readable and machine-parsable.

RESTful APIs can function as either services or clients, depending on their role in the system. As a service, an API exposes endpoints that other applications can call to retrieve or manipulate data. For example, a weather API might provide current conditions and forecasts to any app that requests them. As a client, an API can consume other services—such as a backend system calling a payment gateway API to process transactions. This duality allows RESTful APIs to be modular and composable, enabling complex systems to be built from smaller, interoperable components.

The flexibility and clarity of RESTful APIs make them a cornerstone of modern web development. They allow developers to build applications that are decoupled, maintainable, and scalable across platforms and devices. Whether you're designing a frontend that fetches data from a backend service or integrating third-party tools like social media logins or payment processors, RESTful APIs provide a reliable and efficient way to connect the dots.