Find duplicate JSON keys

Why duplicate JSON keys are dangerous

JSON syntax can contain the same property name more than once inside an object, but object parsers commonly retain only one occurrence. That makes duplicate keys a data-loss risk even when a document appears to parse successfully.

This checker reports every duplicated path and source location without converting the document into a JavaScript object. Your original values and their order remain in the browser.

How to use this tool

1. Paste or upload JSON containing the object you want to inspect.
2. Review each duplicated JSONPath and every line and column.
3. Rename or remove the unintended occurrence before another parser sees it.

Example

{"mode":"first","mode":"second"}

$.mode — 2 occurrences; many parsers keep only the final value.

Common problems

• Duplicates are scoped to one object; the same key in different objects is normal.
• Case matters: id and ID are different property names.
• JSON.parse does not preserve earlier duplicate values.

Useful tips

• Check API fixtures before committing them.
• Treat duplicates as errors unless a receiving system documents otherwise.
• Review generated JSON before parsing it into an object.