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Tools / Validators & Inspectors

JSON validator

Check JSON syntax and the parser’s duplicate-key and numeric constraints.

Input

0 UTF-16 code units

Optional local draft

Saving stores a plaintext draft in this browser on this device. Do not save secrets or use this on a shared device. Nothing is saved or loaded automatically. Reset does not delete a saved draft; use Delete local draft.

No draft has been loaded.

Import a local text file

Output

Work through the task
Check the parser’s JSON syntax, duplicate-key and numeric constraints.
  1. Paste one complete JSON value and choose Check JSON.
  2. A valid result is a parser check, not a schema or business-rule check.
  3. Review the result before copying or downloading. Editing an input invalidates the previous result; keep an original if the transformation matters.
Example to check
{"v":true} is valid. {"v":1,"v":2} is rejected because the key is duplicated.
Limits and output behavior
Up to 100,000 input characters, 10,000 values and 40 data levels. Strict JSON rejects duplicate keys, trailing commas, nonfinite numbers and unsafe integers; quote large identifiers to retain their digits.
Troubleshooting
Check the first syntax/duplicate-key diagnostic and its location. Comments, trailing commas and unsafe integers are rejected even if another application accepts them.
Questions
Does a valid result prove that my application accepts the document?
No. It checks the supported JSON parser constraints. Application schemas and business rules are outside this tool.
Input and privacy
Processing runs in this browser. Inputs are not saved automatically. An explicitly chosen local draft, where offered, is plaintext storage on this device. Downloaded files, clipboard contents and browser extensions have separate retention behavior.