Short definition

API — a defined interface through which software systems exchange data or invoke permitted functions under agreed rules.

Also known as: Application Programming Interface, programming interface.

An API defines how software systems communicate. Instead of accessing each other’s data stores directly, both sides agree which requests are allowed and what response to expect.

How does an API work?

A website sends a request to an endpoint with the required parameters and, when needed, authentication. An HTTP API usually responds with structured data and a status code that indicates the outcome. A good integration handles success, invalid input, rate limits and outages explicitly.

What does this mean for a small business?

API integrations are useful when data already exists in an accounting package, CRM, online store, scheduling tool or CMS. They prevent duplicate data entry, but also create a dependency: pricing, usage limits and API versions can change. Record which system is the source of truth for each data item and what happens when the integration goes down.

What should you check in an API integration?

  • use the smallest possible set of permissions;
  • validate data before storing or publishing it;
  • set timeouts, handle error responses clearly, and limit retry attempts;
  • never store secret keys in browser code or public files;

How it relates to other website choices

A headless CMS delivers content through an API. A webhook is triggered by an event in the source system, while a conventional API call is initiated by the system requesting data or an action.