What kinds of problems does the validator detect?

Syntax errors (with line and column), duplicate object keys, unterminated strings, invalid escapes, trailing content, and numbers that may lose precision.

Does it detect duplicate keys?

Yes. Native JSON.parse silently keeps only the last duplicate; this validator reports each duplicate key as a warning with its location.

Is the validation standards-compliant?

Yes. It follows RFC 8259, the JSON interchange standard.

JSON Validator

Check whether your JSON is valid and pinpoint exactly where problems are. The validator reports the line and column of syntax errors and warns about duplicate keys and integers that exceed safe numeric precision.

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Processed locally in your browser

Inputjson

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Results

Results will appear here after you run a check.

JSON○ Not checked0 lines0 chars0 B

How to use the json validator

Paste or upload the JSON you want to check.
Validation runs automatically as you type (debounced) and on demand with the Validate button.
Errors show the precise line and column. Click a location to jump to it in the editor.
Warnings flag duplicate keys and numbers that exceed safe integer precision.

Example: Catching a trailing comma

Input

{
  "a": 1,
  "b": 2,
}

Output

Error at line 4, column 1: Expected a string key.

JSON does not allow trailing commas; the validator points to exactly where the parser fails.

Frequently asked questions

What kinds of problems does the validator detect?: Syntax errors (with line and column), duplicate object keys, unterminated strings, invalid escapes, trailing content, and numbers that may lose precision.
Does it detect duplicate keys?: Yes. Native JSON.parse silently keeps only the last duplicate; this validator reports each duplicate key as a warning with its location.
Is the validation standards-compliant?: Yes. It follows RFC 8259, the JSON interchange standard.