A Developer Guide to JSON Formatting and Validation

JSON (JavaScript Object Notation) is the most widely used data format on the web. Every REST API, every configuration file, every data pipeline touches JSON at some point. Yet developers routinely lose time to formatting issues, validation errors, and syntax mistakes that are easy to avoid. This guide covers everything you need to know about working with JSON effectively — from common errors to validation best practices. JSON Syntax Rules (The Complete List) JSON's syntax is intentionally minimal. Here are all the rules: Strings must use double quotes ( " ), never single quotes Keys must be strings (double-quoted) Values can be: string, number, boolean ( true / false ), null , object, or array No trailing commas — the last item in an object or array must not have a comma after it No comments — // and /* */ are not valid JSON No undefined — use null instead Numbers cannot have leading zeros (except 0 itself) or trailing decimal points No hex numbers — 0xFF is not valid JSON No single-li