What is JSON Validation?

JSON validation is the process of checking whether a string of text follows the JSON (JavaScript Object Notation) format rules. A valid JSON document must be parseable by a JSON parser — any deviation from the syntax rules will result in a parse error.

Common validation errors include:

Trailing commas after the last element in an array or object
Single quotes instead of double quotes for string values
Unquoted property names (JSON requires strings as keys)
Comments (not allowed in standard JSON)
Missing quotes around values

How to Validate JSON

Our JSON validator tool checks your JSON and returns detailed error messages including the line number and column where the error occurred. Simply paste your JSON and click Validate.

Try it at jsonfmt.bkkdev.io

Common JSON Validation Errors

Unexpected token

Usually caused by a trailing comma, a typo, or an invalid character outside the JSON structure.

Unexpected end of JSON input

Means the JSON is incomplete — a bracket, brace, or quote is not closed properly.

Expected property name or }

Often caused by a trailing comma or using single quotes instead of double quotes.

JSON vs JavaScript Objects

JSON looks similar to JavaScript object notation but they are not the same. Key differences:

JSON keys must always be double-quoted strings
JSON does not allow comments
JSON does not allow trailing commas
JSON values can only be: string, number, boolean, null, array, or object
No functions, undefined, or symbols allowed in JSON

When to Validate JSON

API Development: Validate request/response bodies before sending
Configuration Files: Check package.json, tsconfig.json before running
Data Import: Ensure imported data is valid before processing
Debugging: Pinpoint exact syntax errors quickly

JSON Validator