What is an API?
Corbin Brown
2 min read
Part of the Vibe Coding Fundamentals video series on YouTube.
API stands for Application Programming Interface, which explains nothing, so here's the version that does: an API is a menu plus a waiter. A service like Stripe publishes a menu of things it can do — charge a card, refund a payment, list a customer's invoices. Your app orders off that menu, the waiter (an HTTP request) carries the order over, and the kitchen sends back a response. Your app never enters Stripe's kitchen; it just orders.
Why this is the most useful word in vibe coding
Because it's how your app gets superpowers without you building them. Payments (Stripe), email (Resend), AI responses (OpenAI, Anthropic), maps, weather, text messages — each is a company exposing its kitchen through a menu. When you prompt an agent to “let users pay for a subscription,” the agent's actual work is wiring your app to Stripe's API. Most modern apps are a thin, personal layer over half a dozen APIs, and that's not a shortcut — that's the architecture.
The three things worth knowing
- API keys are your identity when ordering — a password that proves your app is the one being billed. They live in your .env file, never in the code itself, because anyone holding the key can order on your tab.
- Your app has its own API too. When your page loads data or submits a form, the browser is ordering from a menu your agent built — those are the “routes” or “endpoints” it keeps mentioning.
- APIs change. A tutorial from two years ago — or an agent trained on it — may order off an old menu. If the agent writes code against a version that no longer exists, that's not hallucination exactly; it's an outdated menu.
FAQ
What's the difference between an API and a webhook?
Direction. An API is you calling them (“charge this card”). A webhook is them calling you (“that card just got charged”). Real integrations almost always use both.
Are APIs free?
Many have free tiers that cover building and early usage, then bill by volume — per request, per email sent, per token generated. Before wiring one in, ask your agent: “what does this API cost at 1,000 users a month?” It's a question people skip and regret.
The 60-second version
In a hurry? What is API? — the whole idea, as a Short.