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DevUtil

JSON Validator - Check JSON Syntax Online

About the JSON Validator

A misplaced comma or missing quote can break an API integration. The JSON Validator parses your input against the strict JSON spec and tells you exactly what went wrong and where. Paste a webhook payload, a config file, or a database export, and get immediate confirmation that your JSON is well-formed.

The validator runs entirely in your browser, so there is no risk of leaking sensitive payloads to a third-party server. Results appear as you type, providing instant feedback during editing.

How to Use the JSON Validator

Paste or type your JSON into the input area. The validator analyses the input in real time. If the JSON is valid, you will see a green confirmation message. If there is a problem, you will receive a detailed error message that includes the line number and a description of the issue. For example, Expected ',' or '}' at line 12. Fix the reported issue and the validator re-checks automatically.

Features

  • Real-time validation. Errors surface immediately as you type or paste, with no need to press a button.
  • Precise error locations. Line and column numbers point you straight to the offending character.
  • Human-readable messages. Error descriptions are written in plain language, not cryptic parser output.
  • Strict spec compliance. Catches trailing commas, single-quoted strings, comments, and other common mistakes that lenient parsers silently accept.
  • Zero data transmission. Your JSON never leaves the browser, keeping credentials and PII safe.

When to Validate Your JSON

Validation is most useful when JSON crosses a system boundary. Before sending a payload to a REST API, before committing a config file, or after exporting data from a NoSQL database, a quick validation pass catches errors early. It is especially useful when manually editing JSON, since even experienced developers occasionally introduce syntax errors that are hard to spot in a text editor.

Frequently Asked Questions

What counts as valid JSON?
Valid JSON must follow the ECMA-404 standard. It requires double-quoted keys and string values, no trailing commas, no comments, and a root element that is either an object or an array. Numbers cannot have leading zeros and special values like undefined or NaN are not allowed.
Why does my JSON fail validation even though my app works?
Many JavaScript engines are lenient and accept non-standard JSON such as single-quoted strings, trailing commas, or unquoted keys. Strict JSON validation catches these issues because other parsers (like Java, Python, or Go) will reject them.
Does the validator show where the error is?
Yes. When validation fails, the tool displays the line number and character position of the error along with a human-readable description, so you can jump directly to the problem in your editor.
Can I validate JSON Schema with this tool?
This tool validates JSON syntax (whether the document is well-formed). It does not validate against a JSON Schema definition. For schema validation, you would need a dedicated JSON Schema validator.