JSON Validator
Validate JSON syntax instantly with detailed error messages. Format, minify, and inspect JSON structure with key/array counts and depth analysis. Free, 100% in your browser.
Reference
What is JSON validation?
JSON (JavaScript Object Notation) validation checks whether a string conforms to the JSON specification (ECMA-404 / RFC 8259). Valid JSON must have: properly quoted string keys, correct nesting of objects {} and arrays [], valid data types (string, number, boolean, null, object, array), and no trailing commas or comments. This tool uses the browser's native JSON.parse() for accurate validation.
JSON syntax rules
Keys must be double-quoted strings: "key", not 'key' or key. Strings must use double quotes. Numbers can be integers or floats, no leading zeros (except 0.x). Booleans: true / false (lowercase only). Null: null (lowercase). No trailing commas after the last element. No comments — JSON does not support // or /* */ comments. No undefined — use null instead.
Common JSON errors
Missing quotes — keys and strings must be double-quoted. Trailing comma — {"a": 1,} is invalid; remove the last comma. Single quotes — {'a': 1} is not valid JSON. Unescaped characters — special characters in strings (newlines, tabs, backslashes) must be escaped. Duplicate keys — technically valid per spec, but the last value wins and earlier values are lost.
Privacy
All validation runs 100% in your browser using the native JSON.parse() API. No data is sent to any server.