JSON Validator

How to Validate JSON

1. Paste your JSON into the input field.
2. The validator checks syntax in real time — errors are highlighted with the line number and character position.
3. If the JSON is valid, a green confirmation message appears.
4. Fix any errors flagged and re-check.

The validator checks for JSON syntax errors only — it does not validate against a schema (that is, it does not check whether the data has the right fields and types for your specific use case).

The 10 Most Common JSON Syntax Errors

• Trailing comma — {"a": 1,} is invalid. JSON does not allow a comma after the last item in an object or array.
• Single quotes — JSON requires double quotes. {'key': 'value'} is invalid; use {"key": "value"}.
• Unquoted keys — {key: "value"} is invalid. Keys must be quoted strings.
• Undefined — JavaScript's undefined is not a valid JSON value. Use null instead.
• Comments — JSON does not support comments. // comment or /* comment */ will cause parse errors.
• Missing quotes around strings — {"name": Alice} is invalid; string values need quotes.
• Unescaped special characters — backslashes, newlines, and certain Unicode characters in strings must be escaped.
• NaN and Infinity — JavaScript's NaN and Infinity are not valid JSON values.
• Unclosed brackets — every { needs a } and every [ needs a ].
• Extra data after root — a valid JSON document has exactly one root value. Extra content after it is a syntax error.

JSON Schema Validation

Basic JSON syntax validation (what this tool does) confirms the document can be parsed. Schema validation goes further — it checks that the parsed data matches a defined structure: required fields exist, values have the right types, numbers are in range, strings match patterns.

JSON Schema is the standard for describing JSON structure. Popular validators:

• Ajv (JavaScript) — the fastest JSON Schema validator, used by many frameworks
• Zod (TypeScript) — schema-first with excellent TypeScript inference
• jsonschema (Python) — full JSON Schema support
• Newtonsoft.Json (.NET) — includes schema validation

For simple API testing, use this tool for quick syntax checks. For production code, implement schema validation with Ajv or Zod to catch structural problems early.

JSON Syntax Rules Reference

• An object is {} containing zero or more "key": value pairs separated by commas.
• An array is [] containing zero or more values separated by commas.
• A string must be in double quotes and can contain any Unicode character except unescaped " and \.
• Numbers can be integers or floats. Scientific notation (1e10) is supported.
• Booleans are lowercase: true and false.
• Null is lowercase: null.
• Whitespace (spaces, tabs, newlines) is allowed anywhere between tokens.
• No trailing commas after the last element in objects or arrays.
• No comments of any kind.

JSON Processing Tools

Validation is the first step — here is the full JSON workflow:

• Format and prettify JSON once it passes validation
• Convert JSON to CSV for spreadsheet analysis
• Convert JSON to XML for legacy system integration
• Convert CSV to JSON to validate imported data
• Decode JWT tokens — the payload is JSON that can be validated here

Related Tools

• Writing API docs in Markdown? Convert Markdown to HTML to publish your documentation. → convert API documentation from Markdown to HTML
• Passing JSON as a query parameter? URL-encode it first to prevent malformed requests. → URL-encode JSON strings for query parameters
• Need to verify payload integrity? Run the JSON through the Hash Generator to produce a SHA-256 checksum. → generate a checksum for your JSON payload
• Building a scheduled API? Use the Cron Parser to verify your cron expressions are correct. → parse scheduled job cron expressions