A client is a program or device that initiates requests to a server in a networked system. In web development, the term usually refers to web browsers, mobile apps, or other software that calls APIs. The client is responsible for presenting information to users and sending user actions as requests back to the backend. Clients typically communicate with servers using HTTP or other network protocols. They may cache data, handle offline modes, and manage local state for a better user experience. Every time you open a website or call an online service, you are using a client in a client server architecture.
key characteristics
Clients are often constrained by network latency, device performance, and security restrictions imposed by the platform. Modern web clients written in JavaScript can run complex logic in the browser and interact with multiple APIs. Native mobile clients have additional capabilities such as push notifications, sensors, and background tasks. In some architectures, other backend services can also act as clients when they call external APIs or internal microservices. When designing systems or prompting AI for help, it is useful to be explicit about which code runs on the client and which runs on the server.