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1Clear out junk files and repair common Windows errors2Scan for outdated or missing drivers - takes under a minute3Repair Windows errors before they cause bigger problemsAn application programming interface (API) is a set of rules that lets one piece of software request data or functionality from another. It is a software-facing contract: the provider defines what callers may ask for and what they can expect in return. An API does not have to be a website connection, and not every API is REST-based.
What does API stand for?
API stands for application programming interface. “Interface” here means a defined way for software components to interact—not necessarily a screen or controls that a person uses. MDN describes APIs as features and rules within software that enable interaction through software rather than through a human user interface (MDN Web Docs).
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An API is a contract between the software that offers a capability and the software that uses it. The contract describes available operations or data and the rules for requesting them. It also lets the caller use the capability without needing to know unrelated details about how the provider implemented it. IBM explains this integration-focused view in its API overview.
How does an API work?
A client follows the API’s rules to request an allowed operation or resource. The provider processes that request and returns a result, or otherwise responds according to the interface. For a network API, the client and provider communicate over a network; the API’s rules and access controls determine what the client can request. AWS describes an API as defining the rules a caller must follow to communicate with other software systems (AWS: What is an API?).
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- The provider exposes a capability. It decides which data or functions are available through the API.
- The client makes a request. It uses the interface’s expected structure and asks for an allowed operation or resource.
- The provider responds. It returns the requested result or another response defined by the interface.
- The client uses the result. The calling software can present the data, act on it, or combine it with other functions.
For example, a weather app can request forecast information from a weather service and display the returned data. The app does not need to know how the service gathers or stores that information; it needs to follow the API’s request rules and handle the response.
Is every API a web API?
No. API is the broad term. A web API is an API used through web or network technologies, while other APIs may be available within a browser, an operating system, or a software library. MDN’s glossary gives examples such as the browser’s Geolocation API and Web Animations API (MDN Web Docs).
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A browser API lets code use a capability provided by the browser or device, subject to the relevant rules and permissions. A library API exposes functions that other code can call. Neither example needs to be a remote website connection. In contrast, an app requesting data from a weather service is using a network-facing API.
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Is every API a REST API?
No. REST is one architectural style used for some web APIs; it is not another name for API. A REST API follows REST principles, while APIs can use other interaction styles or exist without being web APIs at all. AWS describes REST as a type of web API (AWS: What is an API?).
The Australian Government API Design Standard defines a RESTful API within the scope of that standard as communication in which resources are identified by URIs and operations use HTTP methods (Australian Government API Design Standard: Definitions). That is a scoped definition of RESTful APIs, not a universal definition of every API.
Independent reader supportYour contribution helps us test, update, and keep practical guides available for everyone.What should you look for when someone says “API”?
The word alone does not tell you what an interface can do or how to use it. To understand a particular API, check:
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- Purpose and capabilities: what data or functions it makes available.
- Interaction style: whether it is local to a program or browser, or accessed over a network, and what architectural rules it follows.
- Request and response rules: what a caller must send and what results it can receive.
- Access controls: which callers are permitted to use which operations or resources. AWS AppSync’s explanation discusses APIs in terms of clients, resources, and access controls (AWS AppSync documentation).
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