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JSON Validator
Validate JSON syntax and duplicate keys locally
Check JSON syntax, line and column diagnostics and duplicate object keys without changing or uploading the original source.
Result
Valid JSON source
No output yet.
Processing stays inside this browser.
Instructions
How to use JSON Validator
Paste or choose JSON, then select Validate JSON. Valid source remains available unchanged for copying or download.
Real input and output example
{"name":"first","name":"second"} is valid syntax but produces a duplicate-key warning with both source locations.
Diagnostics and limitations
What this tool reports clearly
Syntax validation does not enforce a JSON Schema. Use JSON Schema Validator when fields and value constraints matter.
Privacy
Files are read with browser APIs and processing runs in a dedicated local Worker. Your JSON is never placed in a network request.
FAQ
Common question
Why warn about duplicate keys?
Many parsers silently retain only the final value, so both locations are reported before parsing.