JSON Validator
Catch JSON errors before they reach production. Syntax validation, JSON Schema support, and precise error messages — free in your browser.
How to Use the JSON Validator
- 1
Paste your JSON into the left panel of the editor above.
- 2
JSON Flash immediately highlights any syntax errors with inline markers.
- 3
Click on an error marker to jump to the exact line and see a human-readable explanation.
- 4
Optionally paste a JSON Schema into the Schema panel to validate structure and types.
- 5
Fix any reported violations and re-validate until the green "Valid JSON" badge appears.
Key Features
Syntax Validation
Detects every JSON syntax error — missing commas, unquoted keys, trailing commas — with the exact line and column.
JSON Schema Support
Validate structure, required fields, types, and custom constraints against any JSON Schema draft (04 through 2020-12).
Human-Readable Errors
Error messages explain the problem in plain English, not cryptic parser output — so you fix issues faster.
Real-Time Feedback
Validation runs on every keystroke so you see errors as you type, not after you submit.
Why JSON Flash?
- Supports all four JSON Schema drafts — no configuration needed.
- Error messages explain the why, not just the where.
- Runs entirely in your browser — no data sent to a server.
- Validates API responses from URLs on the Pro plan.
- Free with no rate limits for syntax validation.
Frequently Asked Questions
What does a JSON validator do?
A JSON validator checks whether your JSON text conforms to the JSON specification (RFC 8259). It reports syntax errors — such as missing quotes, trailing commas, or unmatched brackets — along with their exact line and column numbers.
What is JSON Schema validation?
JSON Schema is a vocabulary that describes the structure of JSON data. Schema validation checks that your JSON has the required fields, correct data types, and any additional constraints you define. JSON Flash supports JSON Schema draft-07, 2019-09, and 2020-12.
Is this JSON validator free?
Yes. Syntax validation is free with no limits. JSON Schema validation is free for schemas under 100 KB. Pro users get unlimited schema validation plus batch validation of multiple files.
Why does my JSON fail validation even though it looks correct?
Common causes include: a trailing comma after the last array element or object property (not valid in JSON, only in JSON5), single-quoted strings instead of double-quoted, or a stray Unicode BOM at the start of the file. JSON Flash's error messages identify the exact cause.
Can I validate JSON against my own schema?
Yes. Paste your JSON Schema into the Schema panel and click Validate. JSON Flash will report every violation with the path to the failing property and a human-readable explanation.
What JSON Schema versions are supported?
JSON Flash supports JSON Schema draft-04, draft-07, 2019-09 (draft-08), and 2020-12. The validator auto-detects the version from the $schema keyword in your schema document.
Can I validate JSON from a URL or API?
Pro users can paste a URL and JSON Flash will fetch the JSON directly and validate it. This is useful for validating live API responses without copying and pasting.
How is JSON validation different from JSON formatting?
Formatting changes the whitespace layout of valid JSON to make it readable. Validation checks whether the JSON is syntactically correct and, optionally, whether it matches a schema. You can format JSON that is already valid, but you cannot validate JSON that has syntax errors.
Related Tools
Unlock Pro — unlimited AI, 10 MB files, API access
Starting at $4/mo · 14-day money-back guarantee
- ✦Batch validate multiple JSON files at once
- ✦Validate JSON fetched directly from a URL
- ✦Custom error message templates
- ✦Schema history saved to your account
- ✦CI/CD webhook integration