Free JSON Validator with Clear Error Messages
Validate JSON syntax and see the exact line, column and reason for every error. Detects duplicate keys and oversized numbers. Runs locally.
JSON Validator tool
Runs entirely in your browser. Nothing you paste is uploaded or stored.
JSON
About this tool
Check whether a JSON document is syntactically valid and, if it isn't, see exactly where and why: line, column and a plain-English explanation such as a trailing comma, a missing quote or an unescaped line break.
Valid documents get a quick summary (objects, arrays, properties, depth) and warnings that JSON.parse would hide: duplicate keys, and integers too large for JavaScript to represent exactly.
How to use it
- Paste JSON or open a .json file.
- Press Validate.
- If there is an error, use Go to line to jump to it, fix it and validate again.
Limitations
- Syntax only; use the JSON Schema Validator for structural rules.
- Inputs up to 25 MB.
Example
{
"id": 1,
"tags": ["a", "b",],
"price": 9.99
}Invalid JSON: Trailing comma before ']' is not allowed in JSON (line 3, column 21)Common use cases
Broken request bodies
Find the stray comma or quote that makes an API return 400 Bad Request.
Config and fixture files
Validate JSON fixtures and configuration before committing them.
Hidden data problems
Catch duplicate keys and oversized IDs that silently change meaning when parsed in JavaScript.