What is JSON? A quick primer for developers
JSON (JavaScript Object Notation) is the lingua franca of the modern web. Learn its rules, common pitfalls and when to use it.
What JSON actually is
JSON (JavaScript Object Notation) is a lightweight, text-based data-interchange format. It represents structured data as a mix of objects (key–value pairs wrapped in curly braces), arrays (ordered lists wrapped in square brackets), strings, numbers, booleans and the value null. Despite its name, JSON is completely language-independent — nearly every programming language ships with a JSON parser out of the box.
Where you will meet it
JSON is the default payload format for REST and GraphQL APIs, the storage format for many NoSQL databases (MongoDB, Firestore), and the go-to config format for tools such as npm, VS Code and TypeScript.
Common gotchas
Keys must be double-quoted. Trailing commas are not allowed. Comments are not part of the spec. Numbers must be finite (no NaN or Infinity). Fix these three things and 90% of "invalid JSON" errors disappear.
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