JSON Validator
Free online JSON validator. Paste any JSON and instantly see whether it is valid, with precise error messages showing the exact line and column of any problem. Runs entirely in your browser — your data never leaves your machine.
Common JSON errors
Trailing commas
JSON does not allow a comma after the last element.
[1, 2, 3,][1, 2, 3]Single quotes
Both keys and string values must use double quotes.
{'key': 'value'}{"key": "value"}Unquoted keys
Object keys must always be wrapped in double quotes.
{key: "value"}{"key": "value"}JavaScript comments
JSON does not support comments of any kind — remove them.
// comment
{"key": "value"}{"key": "value"}What is a JSON Validator?
A JSON validator checks whether a string conforms to the JSON specification (RFC 8259 / ECMA-404). Valid JSON must have all string keys and values in double quotes, no trailing commas, no comments, correct bracket matching, and only the allowed value types: string, number, boolean, null, array, and object.
Invalid JSON is a common source of parsing errors in APIs, configuration files, and data pipelines. Validators help you pinpoint exactly where a syntax error occurs — whether it is a missing bracket, a trailing comma after the last item, or a JavaScript-style comment that JSON does not support.
This validator uses JavaScript's native JSON.parse() in your browser to check JSON without sending any data to a server. It provides actionable error messages and common error examples to help you identify and fix syntax problems quickly.
Frequently asked questions
What does JSON validation check for?
JSON validation checks that your data conforms to the JSON specification (RFC 8259). This includes checking for properly quoted keys, no trailing commas, no JavaScript-style comments, correct value types (string, number, boolean, null, array, object), and correctly matched brackets and braces.
What does 'unexpected token' mean in JSON?
An 'unexpected token' error means the JSON parser encountered a character it did not expect at that position. Common causes include trailing commas after the last item in an array or object, single-quoted strings instead of double-quoted, unquoted property names, or JavaScript comments (// or /* */) which are not valid in JSON.
What are the most common JSON syntax errors?
The most common JSON errors are: trailing commas (e.g. [1, 2, 3,]), single-quoted strings instead of double-quoted, unquoted object keys (e.g. {name: 'value'}), comments (not valid in JSON), and undefined or NaN values (not valid JSON — use null instead).
Is my JSON data sent to a server when I validate it?
No. This validator runs entirely in your browser using JavaScript's built-in JSON.parse(). Your data never leaves your machine and there are no server calls, making it completely safe to validate sensitive or private JSON.
What is the difference between JSON validation and JSON Schema validation?
JSON validation checks that the text is syntactically valid JSON — it can be parsed without error. JSON Schema validation goes further, checking that the parsed JSON matches a specific structure (required fields, data types, value constraints) defined in a JSON Schema document.
Can this validator handle large JSON files?
Yes, for most practical file sizes. Very large JSON files (tens of megabytes) may take a moment to parse, but the validator runs synchronously in your browser without any file size limits imposed by server upload restrictions.
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