What is JSON and why is it used in web development?

Short answer
JSON (JavaScript Object Notation) is a lightweight text-based data format used to store and exchange structured data between servers and clients. It represents data as key-value pairs (objects) and ordered lists (arrays), using only six data types: strings, numbers, booleans, null, objects, and arrays. JSON is language-independent, human-readable, and supported natively by every major programming language, making it the default format for REST APIs and configuration files.

JSON was formalised by Douglas Crockford in the early 2000s as a simpler alternative to XML for data interchange. Where XML required opening and closing tags, schemas, and extensive verbosity, JSON achieved the same structured representation in a fraction of the characters. A JSON object is syntactically identical to a JavaScript object literal, which is why it integrated so naturally with the web.

The format's six types handle most real-world data needs. Strings are wrapped in double quotes (never single quotes). Numbers are unquoted integers or floats. Booleans are the unquoted literals true and false. Null represents the explicit absence of a value. Objects are curly-brace collections of string keys mapped to any value type. Arrays are square-bracket ordered lists of any value type. These six types nest arbitrarily deep.

REST APIs return JSON almost universally. When you fetch data from a weather API, a payment gateway, or a social platform's API, the response body is JSON. The front-end JavaScript parses it with JSON.parse(), and when sending data to a server, JSON.stringify() serialises JavaScript objects into JSON text for the request body.

JSON is also the dominant format for configuration files (package.json, tsconfig.json, .eslintrc.json) and for structured data in SEO (JSON-LD schema markup). Despite being text-based, JSON parsers are highly optimised in modern runtimes, making parsing performance rarely a concern except at extreme scale.

A JSON formatter and validator is one of the most-used developer tools because raw JSON from APIs is often minified (all whitespace removed) and hard to read. A formatter adds indentation and syntax highlighting, while the validator catches syntax errors like trailing commas or unquoted keys before they cause runtime failures.

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