What is an API?
An API (application programming interface) is a documented way for one piece of software to ask another for data or to take an action. No screen, no clicking.
Also called: endpoint
In plain English
If a tool has an API, Zapier, Make, n8n, or an agent can talk to it. If it does not, you are stuck copying and pasting, or using a person. You rarely write the API. You use a product that already speaks it, and you give that product a key. Ask for a single harmless read before you dream about a full sync. Can the tool list today's jobs, and does the list match the screen a person sees? If the read is wrong, a write will be wrong faster. Write down which calls are allowed. 'Full access' is not a plan. It is a shrug. Write down the error you saw on the first failed call. That sentence is the start of the runbook. Keep the sample response beside it.
How an owner would use it
Before you buy an AI add-on, ask whether it can reach the system that holds the truth: the books, the calendar, the phone. 'It has an API' is the start. 'Whose key, and can it send email?' is the real question.
Common mistakes
'It has an API' does not mean you should write code, and it does not mean every action is exposed. Some APIs can read contacts and cannot create invoices. An endpoint is just the address of one of those calls. Do not give an agent a key to an API you have not tried with one harmless read. If there is no API, stop shopping for an agent and plan a paste or a different system.
A worked example
A two-person video studio
The edit bay is not the CRM
This is an illustration, not a customer result. A new inquiry hits the site. An API call, through Make, creates the contact and the project name in the studio's tracker. The editor may get a draft reply. The tracker, not the chat, is where the lead lives.
Related terms
Prompts and guides
Questions owners ask
What is an API?
An API is how two apps exchange data or actions without a person clicking through screens. Automation tools and AI agents use APIs to reach your other software.
How do I use an API if I do not code?
Use Zapier, Make, or n8n, which call the API for you. You still protect the key and decide which actions are allowed.
Who calls the API, me or the agent?
Usually a connector in Zapier, Make, n8n, or the AI app calls it for you. You approve the key or the login and you decide which calls are allowed. You rarely type the request yourself.
The automation glossary also defines API (Application Programming Interface). Product guides are on AI apps for business.