API

An API is a contract: send a request in this format and you will get a response in that format. It lets systems built by different companies work together without either side seeing the other's inner workings. When your site shows a map, takes a card payment or adds a subscriber to your email tool, it is using APIs.

An API is not a product you see. It is the connection between products. A webhook is a related idea that runs the other way: instead of your system asking, the other system tells you when something happens.

How it works

Your system sends a request to the other service's address and says what it wants, for example "create this customer" or "list today's bookings". The request usually carries a key or token that proves your account is allowed to make it. The service checks the key, does the work and replies, usually with data in JSON format and a status code saying whether it succeeded.

Providers publish documentation describing every request you can make, what each one needs and what it returns. They also set limits, called rate limits, on how many requests you can make in a given period, and some charge per request. Most web APIs follow the REST style, which builds on the same addresses and request types as ordinary web pages.

Because an API is a contract, providers try not to change it suddenly. Many publish versions and announce when an old version will be switched off. Your integration keeps working only as long as it speaks a version the provider still supports, which is why connections need occasional maintenance even when nothing on your side has changed.

Example

A garden centre's website sends each new enquiry to its customer management tool through that tool's API. The enquiry appears in the sales list within seconds, tagged with the page the visitor came from, and nobody retypes anything from email.

Two years later the tool announces that the old version of its API will stop working. The enquiries would quietly stop arriving unless the connection is updated, so the developer moves it to the new version and adds an alert that emails the office if any enquiry fails to send. The form keeps a copy of each submission in the meantime, so nothing is lost.

Why it matters for your business

APIs are how your website stops being an island. They save staff time, reduce copying errors and let you swap tools without rebuilding the whole site. The trade-off is dependency: each API is a service that can change, raise its prices or go down, so it is worth keeping a simple list of which ones your site relies on, whose account each key belongs to and who maintains the connections. Before choosing a new tool, check that its API actually covers the actions you need, because many vendors offer the API only on higher plans or expose only part of what the app itself can do. A few minutes reading the documentation index before you sign up saves an awkward discovery later, such as finding that the one action you needed is missing.

Common mistakes

• Placing secret API keys in front-end code, where any visitor can copy them.
• Building a business process on an API with no plan for what happens when it is unavailable.
• Not keeping a list of which APIs the site uses, whose account they belong to and when keys expire.
• Choosing a tool without checking whether its API offers the features you need.

Questions people ask

Do APIs cost money?

Some are free, many have a free tier with limits, and others charge per request or as part of a subscription. Mapping, messaging, payments and AI services commonly charge by usage. Check the provider's pricing page and set spending alerts where they are offered.

What is an API key?

An API key is a long secret code that identifies your account when your system calls a service. Treat it like a password: keep it on the server, never in public code or emails, and replace it immediately if it may have leaked.

Can I connect tools with APIs without a developer?

Often, yes. No-code automation tools connect popular services through their APIs using a visual editor, which is enough for many small business workflows. Custom or high-volume connections, or ones that touch payments and personal data, usually justify a developer.