LessAI Tools.
GLOSSARY /LESS, BUT BETTER

What Is an API?

An API is an agreed interface through which software can exchange data or use another system's capabilities.

Application Programming InterfaceLast checked:BeginnerEditorial-pack check1 sources
THE 10-SECOND ANSWER

A way for two software systems to talk

An API is an agreed interface through which software can exchange data or call another system's capabilities.

Application Programming Interface

In plain language

An API gives two pieces of software an agreed way to communicate. One system sends a request in the format the API expects, and the other system returns data or performs an available operation.

AWS describes APIs as mechanisms that allow software components to communicate using a set of definitions and protocols. (AWS)

An API is the interface between systems. It is not another name for the server behind it.

An everyday example

An analogy

01Software AThe customer
02APIThe waiter
03Software BThe kitchen

The customer does not walk into the kitchen and cook. They give a request to the waiter, who carries it to the kitchen and brings the result back. This analogy is a simplified way to understand the interface, not a complete description of API architecture.

Where you will encounter it

APIs appear in app integrations, developer documentation, automation tools and AI products that retrieve data or trigger outside actions. You may also see API keys used to authenticate access to a service.

Should you care

  • General AI users: knowing the idea is enough.
  • Automation users: worth understanding.
  • Developers: essential.
  • People connecting AI to business systems: important for understanding access and permissions.

How it differs

API vs server: The server runs software and holds or processes data. The API defines how another program can interact with that software.

API vs : An API usually answers “how can software A call software B?” MCP further standardizes how an AI application can discover and use connected capabilities. MCP does not replace all APIs; an MCP server may use APIs underneath.

API vs : An API is a software interface. A RAG system may use an API to retrieve information, but RAG describes a retrieve-then-generate approach rather than a communication interface.

Continue with What is MCP? or What is RAG?.

Related terms

Continue with these published explanations.

Sources & last checked

Sources supplied by the reviewed editorial pack. The check date records our pack cross-check, not a new live verification of these websites. Examples illustrate the concepts.

Official documentation

01
What is an API? — AWSaws.amazon.com

Last checked: September 3, 2026