Why it mattersJSON.parse silently drops duplicate keys within an object (keeps the last), a common trap in config and hand-written JSON. This tool scans and locates every duplicate key.

JSON source

Load JSON

Findings

Duplicate-key findings will appear here

Catch silently dropped keys

JSON Duplicate Key Detector

Locate duplicate keys within an object · line / col positions · local, no upload

🔒Processed locally in your browser — never uploaded or stored

No upload, no storage

JSON is processed in memory and never sent to a server.

Share via URL fragment

Share links encode data in the # anchor — never sent to a server.

Remember last edit

Optionally keep your last input locally; clear it with one click.

Why use a Duplicate Key Detector

Catch duplicate keys

JSON.parse silently drops duplicates and keeps only the last — this tool surfaces them all.

Exact line / col

Every duplicate reports its line, column and object path so you can jump straight to the fix.

Not confused by values

Only duplicate key names within the same object are flagged — identical values are not mistaken for duplicates.

Config sanity check

Hand-written or concatenated JSON often has duplicate keys; scan before shipping for peace of mind.

Local · no upload

Everything runs in your browser; data is never uploaded or stored.