Validate JSON Syntax — With Precise Error Messages
Malformed JSON causes silent failures in APIs, broken configurations, and hours of debugging. The Cluster Tools JSON Validator catches syntax errors instantly, tells you exactly which line and character position the error occurs at, and explains what's wrong.
Runs entirely in your browser using the native JavaScript JSON parser. No JSON data is sent to a server.
Common JSON Syntax Errors
Trailing commas — {"name": "Alice",} — the comma after the last key-value pair is invalid in strict JSON (unlike JavaScript objects and most programming languages).
Single quotes — {'name': 'Alice'} — JSON requires double quotes for all strings and keys.
Unquoted keys — {name: "Alice"} — every key must be in double quotes.
Missing commas between elements — {"a": 1 "b": 2} — elements in objects and arrays must be separated by commas.
Comments — {"key": "value" // comment} — JSON has no comment syntax. Comments cause parse errors.
Incorrect literals — True, False, Null — JSON literals must be lowercase: true, false, null.
Unescaped special characters — literal tabs, newlines, and backslashes inside strings must be escaped: \t, \n, \\.
Step-by-Step: How to Validate
- Paste your JSON into the input area.
- Validation happens as you type — errors are shown in real time with line numbers.
- Fix the errors — the error message explains what's wrong and where.
- A green "Valid JSON" indicator confirms your JSON is syntactically correct.
JSON Validator vs. JSON Schema Validator
Cluster Tools validates JSON syntax — whether the text is correctly-formed JSON according to RFC 8259. It does not validate JSON Schema — whether the data matches a defined structure (required fields, correct types, allowed values).
For JSON Schema validation, you'd use a library like AJV in your code.
Frequently Asked Questions
Is my JSON data safe?
Yes. Validation uses the browser's native JSON.parse(). No data leaves your device.
Can it validate JSON inside a string (escaped JSON)? Not directly. If your JSON is double-escaped (e.g., a JSON string containing encoded JSON), decode it first using the Base64 Decoder or URL Decoder, then validate.
Related Tools
- JSON Formatter — format and beautify JSON after validating.
- JSON Minifier — compact valid JSON for production use.
- Base64 Encoder/Decoder — decode Base64-encoded JSON payloads.