✅ Developer

JSON Validator — Free 2026

Validate JSON syntax, see error line numbers, key count, and nesting depth instantly.

JSON Input

—

Status

—

Total Keys

—

Max Nesting Depth

—

Size

Error Details

—

Formatted Preview

How It Works

Paste your JSON
Click Validate
Review results

Why Validate JSON?

JSON (JavaScript Object Notation) is the universal data interchange format for web APIs, configuration files, and data storage. A single missing comma or mismatched bracket can cause entire applications to fail. This validator instantly checks your JSON against the specification and pinpoints exactly where errors occur, saving you time debugging malformed data.

Common JSON Mistakes

The most frequent errors include trailing commas after the last array or object item (valid in JavaScript but not in JSON), using single quotes instead of double quotes, leaving keys unquoted, including comments (JSON does not support them), and using undefined or NaN values. This validator catches all of these and reports the approximate line number. For more formatting options, use our JSON formatter.

Understanding the Metrics

When your JSON is valid, the tool shows the total number of keys across all nested objects, the maximum nesting depth (how many levels deep the deepest value sits), and the byte size of the input. These metrics help you understand the complexity and size of your data structure. For converting validated JSON to spreadsheet format, try our JSON to CSV converter.

JSON vs JavaScript Objects

JSON is stricter than JavaScript object literals. All keys must be double-quoted strings. Strings must use double quotes (not single). No trailing commas are allowed. No comments are permitted. Functions and undefined are not valid values. This validator enforces all these rules per RFC 8259.

Frequently Asked Questions

What does the JSON validator check?

The validator checks that your JSON conforms to the JSON specification (RFC 8259). It verifies proper syntax including matching braces and brackets, correct use of quotes, valid escape sequences, proper comma placement, and valid data types. If invalid, it reports the error with the approximate line number.

What are common JSON errors?

The most common JSON errors include trailing commas after the last item, single quotes instead of double quotes, unquoted keys, missing commas between items, and comments (JSON does not support comments). JavaScript object literals are not valid JSON.

Does the validator format JSON too?

Yes. When your JSON is valid, the validator displays a formatted preview with 2-space indentation. For more formatting options, use our dedicated JSON Formatter tool.

Is my JSON data private?

Yes. Validation runs entirely in your browser using JSON.parse(). No data is sent to any server. It is safe to validate API keys, tokens, configuration files, and other sensitive JSON data.