JSON Duplicate Key Finder
Find keys that repeat within the same object — a problem JSON.parse silently resolves by keeping only the last value.
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About this tool
Technically, JSON allows a key to appear more than once in the same object, but almost every parser (including JavaScript's) just keeps the last value and silently discards the rest — so a duplicate key is usually a mistake worth catching before it causes confusion. This tool scans the raw text character by character, tracking string literals and nesting depth, and flags any key name that repeats within the immediate key list of the same object. A key reappearing at a different nesting level (e.g. the same name used inside a nested object) is perfectly valid and is not flagged.