What is an API?

An API is how programs talk to each other. It is a published list of requests an app will accept from other software, such as requests to look up a customer, create an invoice, or list the day's orders, along with the exact format each request and reply must follow. People use apps through screens and buttons; other software uses them through APIs.

When an automation tool copies a new contact from a web form into a CRM, it is using APIs behind the scenes. It asks the form app for the latest submission, receives the details in a structured format, and then sends a request to the CRM's API to create the contact. The person building the automation picks options on screen, and the tool turns those choices into API requests.

Most APIs require a key or a sign-in, sometimes through a permission screen based on a standard called OAuth, so that only authorized software can use them. An API key works like a password and should be stored and shared with the same care. APIs also have limits, such as how many requests are allowed in a given period, and they only offer what the company behind the app chose to expose.

When an app has an API but no ready-made connector in an automation tool, it is often still possible to connect it by sending API requests directly, usually through a general-purpose web request step. That takes more technical knowledge, including reading the app's API documentation, but it is a common route when a built-in integration does not exist.

An example

An automation uses the accounting app's API to create an invoice whenever a deal is marked as won in the CRM.