API
An API — application programming interface — is a defined contract that lets one piece of software request data or actions from another without sharing its internals.
You send a request in a shape both sides agreed — a URL, a method, a payload — and you get a structured response, or a clear error. The useful ones are boring: versioned, documented, and stable enough that a client written last year still works.
Almost every modern stack is APIs glued together. A headless CMS is an API for content. Stripe is an API for money. n8n spends most of its life calling other people's APIs and reacting to webhooks.
A sloppy API becomes the product. Undocumented fields, breaking changes, and auth that only works from one laptop are how integrations rot. When we wire tools, we treat the API as a dependency with a contract — not as a private shortcut into someone else's database.
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