An instant API lets you call Wolfram Language code in the Wolfram Cloud from a web URL. You create an instant API and deploy it on the web using the Wolfram Language functions APIFunction and CloudDeploy. Instant APIs can be private (so only you can use them) or public (so anyone can use them). Note: running an instant API uses Wolfram Cloud Credits from your account.

This sets up an API that finds the square of an integer and deploys it to the cloud:

Here is how you can run the API from a web browser:

An API requires three things: a specification of parameters and their types, a specification of the code the API should run, and a specification of how the result from the API should be returned.

The Wolfram Language supports many types of parameters, as listed here.

This creates an instant API that has a parameter called "name" representing a country and that returns a PNG:

Here is the result from calling the API from a web browser:

You specify the code for an API to run as a pure function, with parameter names given as #name and an & at the end to indicate that it is a pure function.

This deploys an instant API that uses parameters x and y as numbers and whose code adds these numbers together:

You can specify permissions for an API deployment; this makes the API public:

If you call an API without parameters in a web browser, you get a form:

One way to debug an API is to run it entirely within the Wolfram Language. An APIFunction works like a pure function that takes an association as its argument: