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Application Programming Interface (API)

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descriptionSet of rules and exposed functionality that lets one piece of software interact with another.
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An API is a set of rules and exposed functionality that lets one piece of software interact with another.

It defines what can be requested, what format is expected, and what kind of response or behavior a caller should expect in return.

What it does​

APIs allow software systems to exchange data or trigger actions without a human clicking through a user interface.

They are commonly used to:

  • Read, create, update, or delete data
  • Trigger actions in another system
  • Expose application capabilities to other software
  • Connect a frontend to a backend
  • Exchange data over HTTP, often using JSON

Core concepts​

Interface between systems​

An API is a contract between software components.

It describes what inputs are accepted, what outputs are returned, and what rules govern that interaction.

Not only web APIs​

Many people use API to mean a web API, but APIs exist in many forms.

Operating systems, libraries, frameworks, databases, and cloud services all expose APIs.

Web APIs and REST APIs​

A web API often uses HTTP to expose resources or actions across a network.

A REST API is one common style of web API, but it is not the only one.

Common use cases​

  • Browser apps loading data from a server
  • Integrating one SaaS product with another
  • Automating tasks from scripts or back-end services
  • Mobile apps talking to remote services
  • Plugins and extensions interacting with host software

Practical notes​

  • An API is the interface itself, not the app or service as a whole.
  • Good APIs are predictable, documented, and stable enough for other systems to depend on.
  • Many modern APIs use JSON over HTTP, but APIs are not limited to that format.
  • Access to an API may require authentication, an API Key, a token, or some other authorization mechanism.

Sources Used​

Frequently Asked Questions​

What does API stand for?​

API stands for Application Programming Interface.

Is every API a web API?​

No. Web APIs are one category of API, but many APIs exist entirely inside software libraries, operating systems, or local applications.

Is a REST API the same as an API?​

Not exactly. A REST API is one specific style of API.