noun

API

AY-pee-EYE

API (noun) means an agreed set of rules that lets one piece of software ask another for information or actions — what you can request, how to phrase the request, and what you will get back. Example: “The weather app does not measure anything itself; it asks a met office API for the forecast.”

noun

technical An agreed set of rules that lets one piece of software ask another for information or actions — what you can request, how to phrase the request, and what you will get back.

"The weather app does not measure anything itself; it asks a met office API for the forecast."

"They published an API so other developers could build on top of the platform."

informal, technical By extension, the particular service reached through such an interface, usually over the internet.

"The API was down all morning, so none of our integrations worked."

How to Use API

Learner’s notes

In plain EnglishAn API is an agreed way for two programs to talk to each other.

When to use it

Take the article that matches the spoken form: "an API", because it is said "ay-pee-eye". Almost never spelled out in full outside documentation.

Memory tip

An API is a contract or interface, not a server, a product or a database. The machine answering the request is the server; the API is the agreed language of the request.

Trace the full origin ↓

Easily confused with

SDK → endpoint → webhook → library →

Common pairings

public API REST API API key call an API API endpoint rate-limited API

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Test yourself on “API” A quick quiz — meaning, synonyms & usage →

Fill the Gap

Can you complete this real example?

The weather app does not measure anything itself; it asks a met office _____ for the forecast.

Etymology

An initialism of application programming interface.

Origin: English

Synonyms

View more →

application programming interface interface endpoint set programmatic interface

Related Words

port interface UI

Frequently Asked Questions

What is the difference between an API and a website?

A website returns pages designed for a person to look at; an API returns data designed for another program to process, usually in a format such as JSON. The same company often runs both against the same underlying information.

What is an API key?

An API key is a string of characters identifying who is making a request, so the provider can recognise the caller, apply limits and, where relevant, bill for use. It is a credential, so it is treated like a password rather than shared publicly.

What is the difference between an API and an SDK?

An API is the set of rules for making requests. An SDK, or software development kit, is a bundle of ready-made code and tools in a particular programming language that makes those requests for you. You can use an API without an SDK, but not the other way round.

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