APIs & Authentication
What is an API?
An Application Programming Interface, a contract that lets one program request actions or data from another in a stable, documented way.
An API defines what one piece of software can ask another to do, and how to ask. In modern web development, "API" usually means a web API: a service exposes HTTP endpoints, you send requests with parameters, the service returns JSON. The contract is the documented endpoint list, the parameters each accepts, and the response shapes you can depend on.
APIs solve the integration problem. Instead of every CRM building its own logo lookup, every fintech writing its own merchant categorizer, and every AI app implementing its own scraper, each capability lives behind a stable API and any caller plugs in. The economic story of the cloud is largely a story of APIs replacing in-house implementations.
For developers, the practical API skills are: reading the docs to understand auth and rate limits, building a typed client that handles pagination and errors well, and resisting the temptation to wrap every API in a leaky abstraction. Most production bugs at the integration boundary come from clients that pretended their API was something it wasn't.
In the wild
- →Stripe's payment API,
POST /v1/charges - →Brand.dev's logo API,
GET /v1/brand?domain=stripe.com - →Twilio's SMS API,
POST /Messages.json
How Brand.dev uses api
Endpoints in the Brand.dev API where this concept comes up directly.
FAQ
API vs SDK?
An API is the protocol contract. An SDK is a library in a specific language that wraps the API into idiomatic code. You can call any API without an SDK, SDKs just save you boilerplate.
What's a public vs private API?
A public API is documented and intended for third-party developers. A private (or internal) API powers a company's own products and is not committed to backwards compatibility for outsiders.
How do I learn an API quickly?
Read the auth section, run the "Hello World" curl example, then build the smallest end-to-end task you actually need. Skim the rest of the docs only when you need them.
Related terms
An API that follows REST conventions, using HTTP methods on resource URLs to model create/read/update/delete operations.
A query language for APIs that lets the client specify exactly the fields it wants from a typed graph of data, returned in one round trip.
A user-defined HTTP callback, your URL gets POSTed to whenever an event happens in someone else's system, instead of you polling for changes.
A secret string that identifies and authenticates a client when calling an API, usually passed in a header on each request.
A server-side policy that caps how many requests a client can make in a given window, returning 429 Too Many Requests when the cap is exceeded.