Validate JSON Instantly — Precise Error Detection
Catch syntax errors with exact line numbers. Free, secure, and fully browser-based.
Validation runs entirely in your browser. Your JSON is never sent to any server.
What is a JSON validator?
A JSON validator checks whether a document follows the JSON specification. Even a single misplaced comma or unquoted key will cause parsers to reject the document, leading to silent failures in production APIs.
This validator uses the browser's built-in JSON.parse() and reports the exact line where parsing failed — so you can fix the error in seconds rather than scanning thousands of lines manually.
Common JSON errors and how to fix them
- Trailing comma —
{"a":1,}is invalid. Remove the comma after the last item. - Single quotes — JSON requires double quotes:
{"key":"value"}, not{'key':'value'}. - Unquoted keys —
{key: "value"}is JavaScript syntax, not JSON. Keys must be quoted. - Comments — JSON does not support
// commentsor/* block comments */. Strip them before validating. - Missing comma — Each item in an array or object must be followed by a comma, except the last one.
Frequently asked questions
JSON validation checks whether a string conforms to the JSON specification (RFC 8259). A valid JSON document uses double-quoted strings, correct bracket/brace matching, proper comma placement, and no trailing commas or comments.
The most frequent JSON errors are: trailing commas after the last item in an array or object, single-quoted strings instead of double quotes, unquoted property names, missing commas between items, and unescaped special characters inside strings.
An "Unexpected token" error usually means there is a character at a specific position that the JSON parser did not expect — a trailing comma, an unquoted key, a JavaScript comment, or a single-quoted string. Look at the line number shown in the error and check the character immediately before or after that position.
Yes. The validator uses the browser's built-in JSON.parse() function. Your JSON is processed entirely in JavaScript on your device and is never transmitted to any server.
JSON syntax validation checks that a document is well-formed JSON (correct syntax). JSON Schema validation additionally checks that the data matches a defined structure — types, required fields, allowed values. This tool performs syntax validation.
You can paste or upload JSON files up to 5 MB. Very large documents may take a moment as the Monaco editor loads the content. The validator itself is near-instant for any size.
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