JSON Duplicate Key Finder
Detect duplicate keys that can cause data loss
Instant Scan
Detect duplicates in milliseconds
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JSON Key Deduplicator
Clean up JSON that contains duplicate object keys. Pick a policy (keep first / keep last / merge values) and export the result.
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Runs entirely in your browser — no upload, no wait.
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Your JSON never leaves the tab. Nothing is logged.
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Why deduplication is non-trivial
Two duplicate keys with primitive values are easy — pick one. Two duplicate keys whose values are objects raise a question: do you want to overwrite, or to deep-merge them? The deduplicator supports both strategies and shows a diff before you commit.
Strategies explained
Keep first — earliest occurrence wins. Useful when the second occurrence is a stale override. Keep last — matches default JSON.parse behavior. Useful when you want predictable parity with native parsing. Deep merge — recursively combine duplicate keys whose values are objects. Arrays are concatenated, primitives use last-wins.
Use cases
Cleaning logs that concatenated multiple JSON payloads, normalizing config files after a manual merge, repairing webhook bodies that arrived spliced together.
Edge cases
Duplicate keys with case differences (Name vs name) are not treated as duplicates by default — JSON keys are case sensitive. Toggle "case insensitive" if you need that behavior.
Privacy
Browser-only. No upload.