How to use
- Paste JSON, open a file, or try a sample.
- Review the live report. Select an issue to locate it.
- Correct the input, then copy or download valid JSON.
Syntax checks with a useful next step
JSON validation answers a specific question: can this text be read as one JSON value? The report points to missing separators, incomplete values, invalid escapes, and other syntax problems.
Warnings highlight data that can be interpreted differently by consumers, such as duplicate property names or integers outside JavaScript’s safe range. A warning does not turn syntactically valid JSON into invalid JSON.
What counts as valid JSON?
A document contains one JSON value: an object, array, string, number, boolean, or null. Property names and string values need double quotes. Values in an object or array are separated by commas, with no comma after the last item.
JavaScript expressions are not JSON. Comments, undefined, NaN, Infinity, single quotes, and unquoted property names are not accepted here.
{
"name": "Ada",
"active": true,
}{
"name": "Ada",
"active": true
}Remove the final comma before the closing brace. The validator locates the issue; you decide how to correct it.
Read errors and warnings differently
An error blocks a usable result. Select its location to focus the relevant input, and fix the earliest error first: one missing quote can lead to several later diagnostics.
Duplicate names are permitted by the JSON grammar, but consumers disagree about which value to use. DevToolsy preserves every occurrence and reports a warning. Numeric-range warnings similarly call attention to a consumer limitation, rather than a syntax error.
Syntax validation and schema validation
Valid syntax does not prove that an API payload contains the right fields or values. A schema can describe required properties, value types, and other constraints. This validator checks syntax and the warnings described above; it does not evaluate JSON Schema or application rules.
Up to 5 MiB of UTF-8 input, 20 MiB of output, 128 nesting levels, 250,000 scanned tokens, and 10 seconds per run. Large documents may need a more capable device.
Frequently asked questions
Does validation run automatically?
Yes. The report updates after a brief pause while you type. Turn off Auto validate to run manually with Validate JSON or Ctrl/⌘ + Enter. Your input stays unchanged.
Does valid JSON have to be an object?
No. A top-level array, string, number, true, false, or null is also a valid JSON document. An empty editor is not.
Are duplicate keys a syntax error?
Duplicate names are allowed by the JSON grammar, but software may choose different values or reject the document. They appear as warnings here and are preserved in exports.
Does validation check my JSON Schema?
No. This tool checks strict JSON syntax and interoperability warnings. It does not check required fields, JSON Schema, or your application’s business rules.
Does the validator fix my JSON automatically?
No. Diagnostics show where to look, and selecting one focuses that part of the input. The broken sample offers a quick way to try this without changing your own data.
Why are there several errors for one mistake?
A missing quote, comma, or closing bracket can disrupt the rest of the parse. Fix the first error and let the report update before working through the remaining list.
What can I export after validation?
For valid JSON, copy or download the checked input. Original whitespace and tokens are retained, except for a leading byte-order mark, which is removed with a warning. Invalid input is not offered as a validated export.
Does my JSON leave my device?
No. Pasted text and local files are processed in your browser. DevToolsy does not upload documents or save a document history. Download a result before leaving the page if you need to keep it.