What Is an API? A Plain-English Guide for Business Owners
Published 7 min read
On this page 9 sections
When we talk about APIs, we often see a frown appear. So, what is an API? It is a set of rules that lets one piece of software ask another for information, or ask it to do something, without a person in the middle. It's a short and sweet term, but not easily understood, so we break it down for you.
API stands for application programming interface. You don't need to know how to write one to make good decisions about them. You just need to know what they do, when they help, and what to ask before you rely on one.
Short answer
- An API is a published set of rules that lets two systems talk to each other.
- You already use them every day: online payments, maps on websites and online sales that appear in your accounts all work through APIs.
- Use an API when you're copying data between systems by hand, or when you want two tools to work as one.
- The main benefits are less admin, fewer mistakes, faster service and the freedom to pick the best tool for each job.
- APIs need to be secured properly, especially when they carry personal information.
What is an API in plain English?
Think of a restaurant. You don't walk into the kitchen to cook your own meal. You look at the menu, tell the waiter what you want, and the waiter brings it back. The kitchen stays private, and you only get what is on the menu.
An API is the waiter and the menu. The "kitchen" is another system, such as your accounting software or a payment provider. The API lists what you're allowed to ask for (the menu) and carries the request and the answer back and forth (the waiter).
MDN, the web reference run by Mozilla, describes an API as a contract between the application offering it and other software (opens in a new window). The system that offers the API decides the rules. Anyone who follows those rules can connect to it.
How a request works
Most modern web APIs follow the same simple pattern:
- Your system sends a request, for example "give me all unpaid invoices".
- The request includes a key or token that proves who is asking.
- The other system checks the request is allowed.
- It sends back an answer in a standard format that software can read, usually JSON. All of this happens in a fraction of a second, and nobody has to export a spreadsheet.
Examples you already use
You meet APIs every time you shop or book online. A few common ones:
| What you see | What the API does |
|---|---|
| A card payment on a website | The site asks the payment provider to take the payment and confirm it worked. Yoco's Checkout API (opens in a new window), for example, sends the customer to a secure payment page and then reports back whether the payment went through. |
| A map on a contact page | The page asks a map service, such as the Google Maps APIs (opens in a new window), to draw the map. |
| An online sale showing up in your books | The shop sends the sale to your accounting system. Xero's Accounting API (opens in a new window), for example, can read and create invoices. |
If your website takes payments or bookings, it almost certainly relies on at least one API already.
When should you use an API?
An API is worth looking at when you see one of these signs:
- Someone retypes the same data into two systems. For example, orders from the website keyed into the accounting package every morning.
- Reports take days because the data lives in different places. Sales in one tool, stock in another, staff hours in a spreadsheet.
- Customers wait for answers your systems already have. Order status, delivery dates or account balances.
- You want to add a new tool without replacing the old one. A modern booking system next to an older back-office system, for instance.
- You want to offer your data or service to partners. Suppliers, resellers or a mobile app. If none of these apply, you may not need one yet. A simple export now and then can be fine for small volumes.
Ready-made connectors or a custom integration?
Many tools already connect to each other with a few clicks, and automation tools can link popular apps without much code. That is often the cheapest place to start. A custom integration makes more sense when your systems are older or niche, when the data needs checking or reshaping on the way through, or when the connection is central to how you make money.
The benefits of APIs
- Less admin. Data moves on its own, so your team spends time on customers instead of copying and pasting.
- Fewer mistakes. No retyping means no typos in prices, quantities or account numbers.
- Faster service. Information is up to date in every system, often within seconds.
- One source of truth. When systems share data through APIs, it becomes much easier to build reliable reports and dashboards.
- Freedom to choose. You can use the best tool for each job and connect them, instead of being stuck with one vendor that does everything averagely.
- Room to grow. A new app, partner portal or sales channel can plug into the same API instead of starting from scratch. APIs are not only a technical concern. In Postman's 2025 State of the API survey of more than 5,700 developers and API professionals, 64.5% said APIs generate revenue for their organisation (opens in a new window).
APIs and AI
AI tools also connect to your business through APIs. When an AI assistant looks up an order, books a meeting or drafts a quote from your price list, an API is doing the fetching behind the scenes. The same Postman survey found that 24.3% of developers already design APIs with AI agents in mind.
The better your APIs, the more safely and usefully you can add AI to your business later.
What to watch out for
APIs open a door between systems, so that door needs a good lock.
- Security. The OWASP API Security Top 10 (opens in a new window) lists the most common API risks. The top one is broken object level authorisation: an API that lets one user see another user's records just by changing a number in the request.
- Personal information. If an API carries customer or staff details, POPIA applies. Section 19 (opens in a new window) requires reasonable technical and organisational measures to keep that information safe.
- Limits and costs. Some providers cap how many requests you can make, or charge per request. Check before you build.
- Change. Providers update their APIs. Someone needs to watch for notices and keep the connection working.
- Documentation. Good APIs come with clear documentation. If a vendor can't show you theirs, treat that as a warning sign.
Questions to ask before you connect two systems
| Question | Why it matters |
|---|---|
| Do both systems have an API, and is it documented? | No API means a workaround, which is usually slower and more fragile. |
| What data needs to move, and how often? | Real-time and once-a-day connections are built very differently. |
| Which system is the master copy? | Prevents two systems overwriting each other. |
| Is personal information involved? | Decides the security and POPIA steps. |
| What happens if the connection fails? | You need alerts and a way to catch up. |
| Who looks after it once it's live? | APIs change, and someone has to keep up. |
How we can help
We design, build and connect APIs for South African businesses, from linking a website to accounting software to connecting older back-office systems with new tools. Our team works with REST and SOAP APIs, event streaming with Kafka, and automation tools such as n8n and Node-RED. You can read more about the team and how we work.
If you're copying data by hand or juggling systems that don't talk to each other, see our software development services or get in touch and we'll tell you what your systems can already do.
Facts checked on 26 October 2026. Sources: MDN Web Docs (opens in a new window), Yoco Checkout API (opens in a new window), Xero Accounting API (opens in a new window), Postman 2025 State of the API Report (opens in a new window), OWASP API Security Top 10 (opens in a new window), POPIA section 19 (opens in a new window).