JSON is a strict text format for structured data—invalid syntax breaks APIs, configs, and `JSON.parse`. Paste a payload to validate it locally, see the exact error location, optionally auto-fix common issues, and copy prettified output.
JSON is a strict text format for structured data—invalid syntax breaks APIs, configs, and `JSON.parse`. Paste a payload to validate it locally, see the exact error location, optionally auto-fix common issues, and copy prettified output.
Runs locally in your browser. No data stored. No signup required.
A JSON validator checks whether a string conforms to the JSON specification, returning a pass/fail result with the exact line and column of any syntax error.
JSON (JavaScript Object Notation) has strict syntax rules: keys must be double-quoted strings, values must be strings, numbers, objects, arrays, booleans, or null, and trailing commas are not allowed. A JSON validator parses the input against these rules and reports whether it is syntactically valid.
Unlike a JSON formatter (which beautifies valid JSON), a validator's primary job is detecting errors. It tells you exactly what is wrong and where — useful when a malformed payload is causing an API to return a 400 error, a config file is failing to parse, or you're debugging a JSON string that looks correct but isn't.
Concise answers for common searches — definitions, steps, and comparisons.
Trailing commas are not valid in JSON. {"a": 1, "b": 2,} and [1, 2, 3,] both produce a SyntaxError in JSON.parse(). This is one of the most common JSON errors — trailing commas are legal in JavaScript object literals and most modern languages, but ECMA-404 (the JSON spec) explicitly forbids them. Remove the comma after the last element in any object or array.
No. JSON does not have an undefined value. The six valid JSON value types are: string, number, boolean (true/false), null, object, and array. If you need to represent an absent value, use null. JSON.stringify() silently drops object properties whose value is undefined — they are not converted to null, they disappear entirely from the serialized output.
JSON validation checks whether text is syntactically valid JSON — correct quotes, no trailing commas, paired brackets. JSON Schema validation checks whether a valid JSON document matches a structural contract: required fields, data types per field, value ranges, and array item shapes. JSON Schema is a separate tool; this validator handles syntax only. A document can be valid JSON but fail JSON Schema if it lacks a required field.
Copy and paste the JSON string you want to validate into the input field. It can be any size — minified, formatted, or broken.
The validator instantly checks syntax and shows a green 'Valid JSON' badge or a red error message with the exact line and column of the problem.
Use the error location to find and fix the issue in your source. Common fixes: add missing commas, replace single quotes with double quotes, remove trailing commas.
Common real-world scenarios where this tool saves time.
Validate JSON configs (CI/CD pipelines, server settings, feature flags) before deploying to avoid runtime parse errors.
Verify that JSON payloads sent to or received from third-party APIs conform to valid JSON syntax before further processing.
When an API call returns a 400 error, paste the request body here to find malformed JSON that caused the rejection.
Perfect for developers new to JSON — paste examples and get immediate, precise feedback on syntax rules.
Step-by-step chains that connect related tools for common tasks.
Run validation before formatting whenever the source might be JavaScript object syntax, a truncated API response, or copy-paste from Slack.
Input
{"name": "Alice", "age": 30, "active": true}Output
✓ Valid JSONAll keys are double-quoted, values use correct types (string, number, boolean), and there is no trailing comma. The validator confirms it is syntactically correct.
Input
{"name": "Alice", "age": 30,}Output
✗ Error: Unexpected token "}" at line 1, column 29The trailing comma after 30 is the most common JSON mistake — JavaScript allows it in object literals, but JSON does not. Remove the comma after the last property.
Input
{'name': 'Alice'}Output
✗ Error: Unexpected token "'" at line 1, column 2JSON requires double quotes. Single-quoted strings from Python dicts or JavaScript objects are not valid JSON. Replace all single quotes with double quotes.
The tool attempts JSON.parse on your input after optional cleanup. A successful parse means the text matches the JSON grammar; a thrown SyntaxError means the engine rejected the structure at a specific position.
Formula
JSON value → object | array | string | number | true | false | null
String → " characters "
Object → { pair (, pair)* }
Array → [ value (, value)* ]| Related tool | Use this tool when | Use related tool when |
|---|---|---|
| JSON Formatter | You need a pass/fail check and the precise byte offset of the first syntax error. | JSON is already valid and you want readable indentation, minification, or download. |
| Regex Tester | You have a complete JSON string to validate against RFC 8259 / ECMA-404. | You only need to extract one field from a log line or non-JSON wrapper — regex extracts text; this tool parses structure. |
Remove the comma before } or ]; JSON.parse rejects trailing commas.
JSON requires double quotes; replace ' with ".
Use null instead of undefined, valid numbers instead of NaN, and strip // or /* */ comments.
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No. Validation runs entirely in JavaScript in your browser. Your JSON — including any embedded credentials or sensitive data — never leaves your device.
Trailing commas (a comma after the last item in an array or object) are the most frequent mistake. JSON does not allow trailing commas, while JavaScript objects do — causing confusion for developers switching between the two.
A validator only checks whether your JSON is syntactically correct. A formatter also beautifies or minifies the JSON. Use the validator for a quick pass/fail check, and the formatter when you also want to clean up the output.
Yes — completely free with no signup, no character limit, and no usage restrictions.
Part of Developer Tools
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