Question 1

How do I validate JSON?

Accepted Answer

JSON is valid if it can be successfully parsed by JSON.parse(). This requires double-quoted keys and strings, no trailing commas, no comments, valid value types (string, number, boolean, null, array, object), and properly balanced brackets and braces.

Question 2

What does 'unexpected token' mean in a JSON error?

Accepted Answer

An unexpected token error means the parser found a character it didn't expect at that position. Common causes: single quotes instead of double quotes, trailing commas, unquoted property names, or JavaScript-specific syntax like undefined or function.

Question 3

Does JSON support comments?

Accepted Answer

No. Standard JSON (RFC 8259) does not support comments. JSON5 and JSONC are extensions that add comment support, but they require special parsers. Many config files (VS Code settings, TSconfig) use JSONC format.

Question 4

Is null valid in JSON?

Accepted Answer

Yes. JSON supports four primitive types: strings (double-quoted), numbers (integers and floats), booleans (true/false lowercase), and null. undefined, NaN, and Infinity are not valid JSON values.

Question 5

What JSON validation is available via API?

Accepted Answer

If you need server-side JSON validation, use programming language parsers (JavaScript's JSON.parse, Python's json.loads, Java's Jackson) which all throw on invalid JSON. JSON Schema validation (using ajv, jsonschema) validates structure beyond just syntax.

Question 6

How do I validate JSON syntax?

Accepted Answer

Paste your JSON above for instant validation. The validator uses JSON.parse() and shows the exact line and column of any syntax error. Common errors: trailing commas, single quotes, unquoted keys, JavaScript comments, and undefined values. All of these are valid JavaScript but invalid JSON. For formatting valid JSON, use DevDecode's JSON Formatter.

Question 7

What is the difference between JSON validation and JSON schema validation?

Accepted Answer

JSON syntax validation checks that your text is valid JSON (proper formatting, no syntax errors). JSON Schema validation checks that the JSON structure matches a defined schema — required fields, data types, value ranges. This tool performs syntax validation. For schema validation, you need a JSON Schema validator. Always start with syntax validation before schema validation.

JSON Validator — Free Online JSON Syntax Checker

Frequently Asked Questions

JSON Validation: Syntax Rules and Common Errors

Related Tools

JSON Formatter

JSON Minifier

YAML to JSON

XML Validator