Free JSON Validator Online - Syntax & Schema Validation
Validate JSON syntax against RFC 8259 with line-level error reporting. Supports JSON Schema Draft 2020-12 for structural validation. All processing happens locally in your browser.
Example data loaded — edit or paste your own JSON below.
JSON Schema (Optional)
How to Validate JSON Online
Step-by-step guide for using the JSON Validator.
- Paste your JSON string into the Input JSON box above.
- Click Validate JSON — the result appears instantly.
- If valid, you'll see a green success message and JSON statistics.
- If invalid, the error panel shows the exact error type, message, and line number.
- Fix your JSON and validate again until it passes.
Common JSON Errors & Fixes
| Error | Example (Wrong) | Fix |
|---|---|---|
| Trailing comma | {"a":1,} |
{"a":1} |
| Single quotes | {'key':'val'} |
{"key":"val"} |
| Unquoted key | {key: "val"} |
{"key": "val"} |
| Missing comma | {"a":1 "b":2} |
{"a":1,"b":2} |
| Comments | {"a":1} // comment |
Remove comments (JSON doesn't support them) |
Frequently Asked Questions
What does a JSON validator check?
A JSON validator checks whether your JSON follows the correct syntax rules, including quotes, commas, brackets, nesting, and value formatting. This tool also supports JSON Schema validation (Draft 2020-12) — enter a JSON Schema to validate your data structure against custom rules.
Can a JSON validator fix broken JSON automatically?
A validator mainly detects errors; if you also want cleanup or repair, pair it with a JSON Formatter or JSON Repair tool.
Why is valid JavaScript object syntax not valid JSON?
JSON is stricter than JavaScript objects and requires double-quoted keys, double-quoted strings, and no trailing commas. Comments are also not allowed in JSON.
Does my JSON get uploaded to a server?
No. All validation runs entirely in your browser using JavaScript. Your JSON data never leaves your device.
What's the difference between validation and formatting?
Validation checks correctness — is this valid JSON? Formatting also beautifies the JSON with indentation. Use our JSON Formatter if you also want to format your output.
Real-World Use Scenarios
Add a JSON validation step to your CI workflow. Validate every API response fixture before deployment — catch a missing closing brace in responses.json before it breaks staging. Pair with JSON Schema to enforce field types and required keys.
Before committing tsconfig.json, .eslintrc.json, or i18n translation files, paste them here to catch syntax errors. One extra comma in a 500-line locale file breaks the entire app — the validator pinpoints the exact line.
When ingesting JSON from multiple sources (Kafka topics, S3 buckets, partner APIs), validate each payload before it enters your data lake. Spot malformed records early — the line-number error reporting makes triage fast.
Input / Output: Invalid JSON with 3 Error Types
This JSON contains three common mistakes. The validator reports each one with the exact line number and a plain-English fix suggestion.
{
"product": "Widget Pro",
"price": 29.99,
"tags": ["tools", "developer", "gadget",],
"specs": {
"weight": "2.5kg"
"color": "black",
},
"color": "blue"
}
"gadget"., after "2.5kg"."black".Common Validation Errors & Fixes
| Error | Example Trigger | Line Reported | Fix |
|---|---|---|---|
| Missing closing brace | {"a":{"b":1} |
Last line of input | Count your { and } pairs. Every { needs a matching }. |
| Trailing comma in object | {"a":1,} |
Line with the trailing , |
Delete the comma immediately before the closing } or ]. |
| Duplicate object key | {"a":1,"a":2} |
Line of the second occurrence | RFC 8259 says keys SHOULD be unique. Remove or rename duplicates — the last value wins silently in most parsers. |
| Unquoted string value | {"msg":hello} |
Line of the bare word | Wrap all string values in double quotes: {"msg":"hello"}. |
| Numeric leading zero | {"id":007} |
Line of the number | JSON forbids octal notation. Use 7 or quote it as "007" if the leading zeros matter. |
Frequently Asked Questions
Can I export the error report?
The error details (type, message, line number, and fix suggestion) are displayed inline in the error panel. You can copy the error text directly from the panel. For bulk validation of multiple files, use the "Copy" button on the output area to grab the formatted valid JSON, or integrate our validation logic — which runs on standard JSON.parse — into your own scripts.
Does this validator support JSON Schema?
Yes. Expand the "JSON Schema (Optional)" panel below the input area and paste your schema (supports JSON Schema Draft 2020-12 via Ajv). The tool validates both syntax and structure — e.g., check that age is an integer, email matches a format, or that required fields are present. Schema errors are reported with the exact instance path.
Can it handle JSON5 or non-standard JSON?
The validator strictly follows RFC 8259. JSON5 features (trailing commas, single quotes, unquoted keys, comments, hexadecimal numbers) will trigger syntax errors. For quick fixes on mildly broken JSON, use the JSON Formatter tool's Repair button. For full JSON5 support, you'll need a JSON5-specific parser like the json5 npm package.
How many errors does it detect at once?
The syntax validator stops at the first parse error (standard JSON.parse behavior). Fix that error and re-validate to find the next one. Schema validation, however, reports all structural violations in a single pass — if 5 fields fail their schema checks, you'll see all 5.
What are the performance limits?
The validator uses native browser JSON.parse — extremely fast for files up to 10MB (sub-second). Between 10-50MB, parse time grows linearly (1-4 seconds). Above 50MB, memory pressure can cause browser slowdowns. Schema validation adds overhead proportional to schema complexity and data size — large schemas with $ref resolution on big datasets may take a few extra seconds.