JSON Validator
Pinpoint syntax errors to the exact line and column — offline.
Your data is processed entirely in your browser and is never uploaded.
Tool workspace
Drag & drop file here or browse
Options
JSON allows repeated keys; most code keeps the last. We warn you.
Append a pretty-printed copy to the report when valid.
Validate JSON in three steps
Paste or upload
Drop in any JSON — validity is checked as you type, up to 15M characters.
Read the diagnosis
Errors point to the exact line and column, with the offending lines and a caret.
Inspect structure
When valid, see a structure tally, duplicate-key warnings, and an optional normalized copy.
Frequently asked questions
Is my JSON uploaded anywhere?
No. Validation runs entirely in your browser (in a background worker for large files). Your data never leaves your machine.
Why are duplicate keys only a warning?
The JSON specification permits repeated keys, and JSON.parse silently keeps the last value — which is usually a bug. We flag them so you can decide, rather than rejecting valid input.
How exact are the line and column numbers?
Exact, and identical in every browser. The validator walks the JSON grammar itself rather than reading an error string, so the coordinates never depend on the engine's message format.