JSON Validator
Check JSON syntax and find errors.
About this tool
JSON syntax errors can prevent applications and APIs from reading data correctly. ToolAlto's JSON Validator checks whether the input can be parsed as JSON so you can separate a syntax problem from an application problem.
How to use it
- Paste your JSON into the input area.
- Run the validation check.
- If the JSON is invalid, review the parser message and fix the syntax.
- Validate again, then use the JSON Formatter if you want a more readable version.
Common JSON errors
Frequent syntax problems include missing commas, trailing commas, mismatched braces or brackets, unquoted property names, incorrect quotation marks, and invalid values such as True instead of true. The JSON validation guide explains these mistakes with a practical troubleshooting workflow.
Validation versus schema checks
This tool checks JSON syntax. A document can be valid JSON but still fail an API's required fields, data types, or business rules. Those application-specific checks are separate from basic JSON parsing.
Privacy
Validation happens in your browser using the built-in JSON parser. The tool does not need to upload your JSON to a ToolAlto server.
Frequently asked questions
What is JSON validation?
JSON validation checks whether a JSON document follows the required syntax and can be parsed.
What errors can JSON validation catch?
It can identify syntax problems such as malformed strings, missing punctuation, invalid values, or incorrectly structured JSON.
Can valid JSON still be rejected by an API?
Yes. Syntax validity does not guarantee that the data meets an API's schema or business rules.
Is the JSON validator free?
Yes. ToolAlto's JSON Validator is free to use online.