JSON Duplicate Key Finder
Detect duplicate keys in raw JSON (valid per parser but often a bug).
What is Dup Keys?
The JSON Duplicate Key Finder scans raw JSON text for duplicate keys. Standard JSON.parse silently keeps only the last value for each key, which can hide bugs. This tool surfaces every duplicate with its line and column so you can fix them.
How it works
We scan the raw JSON text with a regex that finds quoted keys followed by colons, tracking first occurrence for each key. When a key appears again, we report the duplicate with both positions.
- Paste JSON. Paste raw JSON text that may contain duplicate keys.
- Review duplicates. Each duplicate is shown with its key, duplicate position, and first occurrence position.
- Fix and re-check. Edit the input and re-check until no duplicates remain.
Examples
Obvious duplicate
{ "a": 1, "a": 2 } — reports "a" at line 1, column 12, first at line 1, column 3.
Common mistakes
False positives
Keys in different objects are not duplicates. Only keys at the same nesting level are flagged.
Alternatives
JSON Validator
For general JSON syntax validation.
Frequently asked questions
Why use this instead of JSON.parse?
JSON.parse silently keeps the last value. This tool shows every duplicate so you can decide which one is correct.