Client

The software or device that accesses services or resources on a server.

A client is any software application, device, or system that sends requests to a server to access resources or services. In web development, the most common client is a web browser, but clients also include mobile applications, desktop applications, command-line tools, and other servers making API calls.

The client-server model is foundational to how the internet and APIs work. Clients initiate communication by sending requests (typically over HTTP or HTTPS), and servers respond with the requested data or confirmation of an action. This separation of concerns allows clients and servers to evolve independently as long as they adhere to the agreed-upon API contract.

In API management, understanding client behavior is important for setting appropriate rate limits, designing authentication flows, and optimizing response formats. API gateways can identify and differentiate clients based on API keys, OAuth tokens, or IP addresses, and apply client-specific policies such as throttling, usage quotas, or access restrictions.