API

An Application Programming Interface is a set of rules that lets two pieces of software talk to each other. When you log into an app using your Google account, an API handles the handshake between the app and Google behind the scenes. APIs are the backbone of modern web development, enabling everything from payment processing to weather widgets.

Here is a version you have already used without noticing. When a customer pays on your website, your site does not process the card itself — it sends the details to Stripe's API, Stripe does the heavy lifting, and your site gets back a simple answer: paid or declined. The same pattern powers shipping labels, SMS confirmations, calendar bookings, and the map embedded on your contact page.

Why it matters for your project: APIs decide how much of your product you have to build versus rent. If a service already exists — payments, invoicing, email delivery, accounting — connecting to its API is almost always cheaper and more reliable than building your own version. When you brief a developer, the key questions are which tools your business already runs on and whether they expose an API. Good answers there can cut weeks off a build.

Most APIs you will encounter follow the REST style, which is a common convention for how requests and responses are structured. Some also support webhooks, which flip the direction: instead of your system asking for updates, the other service pushes them to you the moment something happens. And when an API needs to act on a user's behalf, OAuth is usually the protocol that grants it permission safely.