JSON Validator
Validate and check JSON syntax. Detailed error reporting with line numbers. Free.
How to use the JSON Validator
Common JSON mistakes
The classic errors: trailing commas ([1, 2, 3,] — JSON doesn't allow them, unlike JavaScript), single quotes (must be double), unquoted keys ({name: "a"} is invalid — keys must be quoted strings), and undefined or function values (JSON only supports strings, numbers, booleans, null, objects and arrays).
Strict standard
JSON is defined by RFC 8259 / ECMA-404. Numbers cannot have leading zeros (other than 0 itself), comments are forbidden, and the top-level value must be an object, array, string, number, boolean or null. This validator follows the strict standard — the same as JSON.parse in every modern browser.
RFC 8259 (the current JSON spec) requires UTF-8 encoding for JSON exchanged between systems. It also explicitly bans trailing commas, comments, and single-quoted strings — which is why valid JavaScript object literals often aren't valid JSON.
Frequently asked questions
What are the most common JSON errors?
Trailing commas, single quotes instead of double quotes, unquoted property names, missing commas between items and comments. JSON is stricter than JavaScript object syntax.
Does the validator show where the error is?
Yes, the error message points to the position of the first problem so you can correct it and validate again.
Is my JSON uploaded?
No. Validation runs in your browser, so API responses and configuration containing sensitive data are not sent anywhere.