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JSON Validator
Check JSON syntax and get a useful error location without changing your data.
Check a complete JSON value for syntax errors and duplicate keys. This is not a schema check: required fields and business rules need separate validation.
Validation keeps your input unchanged. A successful syntax check does not verify required fields, allowed values, or an application schema.
Read the first error in context
The parser reports where it can no longer continue. If a comma is missing, that position may be the start of the next property rather than the exact place the comma belongs. Use Go to error and inspect the preceding token.
{"name":"Ada" "active":true}Valid JSON is not an application contract
One complete object, array, string, number, boolean, or null can be valid JSON. Comments, trailing commas, undefined, and extra content after the value are rejected.
A syntactically valid payload may still be missing a required field or have an invalid quantity. The report explicitly separates syntax from schema checks; no schema is loaded here.
Resolve duplicate-key warnings
The object below is syntactically valid but uses the same key twice. Different consumers can keep different values or reject it. The validator warns without choosing which value to discard.
{"role":"reader","role":"editor"}Validate before formatting or sending
Correct syntax errors and duplicate keys, then inspect application-specific constraints. Use JSON Formatter if you need indentation or minification; this page focuses on validation.
The local worker accepts input up to 2 MB and nesting up to 200 levels. Clear cancels pending work. File content and pasted input are not uploaded.
Frequently asked questions
Can a number alone be valid JSON?
Yes. A JSON document can contain a single number or another complete JSON value; it does not have to be an object.
Does a duplicate-key warning make the syntax invalid?
Not necessarily. The warning identifies an interoperability risk that should be resolved before sending the data.
Will validation change my numeric values?
No. Validation inspects tokens without rounding them into JavaScript numbers. Your application may interpret those tokens differently.
Why did the application reject valid JSON?
Check its schema, required fields, types, ranges, and authorization rules. Syntax validation cannot infer those requirements.