JSON formatter or validator? Start with the failure you have

A formatter makes valid JSON easier to read by changing indentation and line breaks. A validator checks whether the text follows JSON syntax. If a payload will not parse, validate first and repair the reported issue; formatting cannot infer the intended meaning of a missing quote or bracket.

After syntax passes, check the required schema and business rules. A document can be valid JSON while missing a required field or carrying a wrong type. Watch for duplicate keys, which some parsers silently handle differently. Formatting should not change values, so compare parsed structures when fidelity matters. Use trusted tools for sensitive payloads and redact tokens or personal data before pasting them into a public service.