How Do APIs Connect Business Applications?

Most businesses now rely on a collection of software tools, from accounting and stock control to email marketing and customer support. The reason these tools can share information without someone copying it by hand is usually an API. This explainer covers what APIs are, how they work, and what to consider before connecting your own systems.

What an API is

API stands for application programming interface. It is a defined set of rules that lets one piece of software ask another for information or ask it to do something. The API sets out what requests are allowed, what format they must take and what the response will look like.

A common comparison is a restaurant menu. You do not need to know how the kitchen works; you choose from the menu and the order is handled for you. Similarly, an API lets one application use another's features without needing to understand its internal workings.

How two systems exchange data

When an online shop records a new order, it might need to send the details to an accounting package. Through an API, the shop's system sends a request to the accounting software saying, in effect, "create an invoice with these details". The accounting software checks the request, carries it out and sends back a response confirming success or explaining what went wrong.

Many modern APIs follow a style known as REST, in which requests are sent over the web to specific addresses called endpoints. Each endpoint represents something such as customers, orders or products. The data itself is usually formatted as JSON, a lightweight text format that both people and machines can read.

A typical exchange involves:

• A request sent to a specific endpoint, such as the one for orders.

• An action, such as reading, creating, updating or deleting a record.

• Credentials that prove the requesting system is allowed access.

• A response containing the requested data or a confirmation.

• A status code that indicates whether the request succeeded or failed.

Pulling data versus being notified

There are two broad ways systems keep each other up to date. In the first, one system regularly asks another whether anything has changed. This is simple but can be inefficient if checks happen often and little has changed.

In the second, the system where the change happens sends a notification automatically. These notifications are often called webhooks. When a payment is completed, for example, the payment service can immediately tell the shop, which then updates the order status.

Security and access

Because APIs give software access to business data, controlling that access is important. Most APIs require a key or token that identifies the connecting application. Many use OAuth, a widely adopted standard that lets a user grant an application limited access to their account without sharing their password.

Good practice is to grant each connection only the permissions it needs. An integration that only reads product information should not be able to delete customer records. Keys and tokens should be stored securely and replaced if there is any chance they have been exposed.

What to check before connecting your tools

Before linking business applications, it is worth asking a few practical questions:

• Does each tool offer an API, and is it included in your current plan?

• Is there a ready-made integration, or will it need custom development?

• What data will move between the systems, and in which direction?

• Are there limits on how many requests can be made in a given period?

• How are errors handled, and will anyone be told if a connection fails?

• Where is the data stored, and does that meet your privacy obligations?

• What happens if one provider changes or retires its API?

Documentation quality is also a useful signal. Clear, up-to-date documentation usually indicates an API that is actively maintained.

Integration platforms

Not every connection needs a developer. Integration platforms allow users to link popular applications through visual workflows, often using the same APIs behind the scenes. These suit straightforward tasks such as adding new contacts to a mailing list. More complex or high-volume integrations may still benefit from custom development.

The bottom line

APIs are the connectors that let business applications share data and trigger actions in each other. They work by exchanging structured requests and responses under agreed rules. Checking access controls, limits, error handling and data protection before connecting tools will help integrations run reliably and safely.