JSON Duplicate Key Finder
Detect duplicate keys that can cause data loss
Instant Scan
Detect duplicates in milliseconds
100% Private
All processing happens in your browser
No Signup
Free tool, no registration required
JSON Array Duplicate Finder
Scan any JSON array for duplicate items — exact value, by a chosen key, or with a custom equality function.
Instant
Runs entirely in your browser — no upload, no wait.
100% private
Your JSON never leaves the tab. Nothing is logged.
No signup
Free, unlimited, no account required.
Three ways to compare
Strict — values must be deeply equal. By key — pick a property (e.g. id) and treat items as duplicates when that key matches. Custom — write a one-line comparator in JS for full control.
Reading the result
Duplicates are grouped, with the index of every occurrence and the count. A "remove duplicates" action lets you keep the first, last, or merge the items in each group.
Use cases
API pagination bugs that return the same record twice, deduplicating user lists, cleaning seed data, normalizing tags arrays.
Performance
Strict mode uses a stable JSON-canonicalized hash, so even arrays of 100k objects deduplicate in well under a second.
Privacy
All processing is local.