Deploying to the Wolfram Cloud

Prerequisites: Associations

One function, CloudDeploy, turns code into a web API, a form, or a web page on the Wolfram Cloud. You need a Wolfram Cloud account; from a desktop session, connect with CloudConnect[] first.

A web API

(* illustrative: needs a Wolfram Cloud account *)
api = CloudDeploy[
  APIFunction[{"x" -> "Integer"}, #x^2 &],
  "square-api",
  Permissions -> "Public"]

The result is a CloudObject with a URL like https://www.wolframcloud.com/obj/yourname/square-api. Anyone can call it:

https://www.wolframcloud.com/obj/yourname/square-api?x=7

and gets back 49. From the Wolfram Language, URLExecute[api, {"x" -> 7}] does the same.

{"x" -> "Integer"} declares a parameter and its type. The type is an interpreter: the cloud rejects values that aren't integers before your code runs. Other types include "Number", "String", "Date", and "Country".
Parameters reach the function as an association, so #x is the value.
Permissions -> "Public" makes it callable without signing in; the default is private.

Returning JSON

(* illustrative *)
CloudDeploy[
  APIFunction[{"n" -> "Integer"},
    ExportForm[<|"n" -> #n, "square" -> #n^2, "prime" -> PrimeQ[#n]|>, "JSON"] &],
  "number-info",
  Permissions -> "Public"]

Calling it with ?n=7 returns a JSON object with n, square (49), and prime (true). ExportForm chooses the response format — JSON, PNG for a plot, HTML, and more.

A web form

(* illustrative *)
CloudDeploy[
  FormFunction[{"name" -> "String", "year" -> "Integer"},
    "Hello, " <> #name <> "! You will turn " <>
      ToString[2030 - #year] <> " in 2030." &],
  "greeting-form",
  Permissions -> "Public"]

Visitors see a form with two fields, validated by type; submitting it shows the result.

More deployment options

CloudPublish[notebook] publishes a notebook as a web page.
CloudDeploy[Manipulate[...]] makes an interactive web app.
CloudDeploy[ScheduledTask[code, "Daily"]] runs code on a schedule — for example, to fetch data and email a report.
Databins (CreateDatabin, DatabinAdd) collect data sent from devices and other programs.
For your own servers, the Wolfram Application Server runs the same APIs on-premises or in Kubernetes.

Security

Always declare parameter types — never accept raw text and pass it to ToExpression, which would let callers run arbitrary code.
Keep deployments private unless they must be public, and use Permissions to grant access to specific users.
Deployed code runs under your account and uses your cloud credits; limit expensive operations.