Free Online Validators
Validate JSON, XML, YAML, HTML, and more with detailed error reporting. All validation runs client-side — your data stays private.
6 validators available
Validate JSON syntax and structure with detailed error messages.
Check XML documents for well-formedness and syntax errors.
Validate YAML syntax and detect indentation or type errors.
Check HTML markup for common syntax and structure issues.
Validate JSON5 files including comments and relaxed syntax.
Validate JSON Lines / NDJSON files line by line.
What Are Online Data Validators?
Online data validators check whether a document conforms to the syntax rules of its format — catching missing brackets, incorrect indentation, invalid characters, or structural errors before they cause bugs in production.
Our validators provide detailed, line-by-line error messages so you can pinpoint exactly where a problem exists. All validation runs in your browser — no data ever leaves your machine.
Common Use Cases
- check_circleValidate JSON API payloads before sending to production
- check_circleCheck YAML CI/CD pipeline configs for syntax errors
- check_circleVerify XML data files before importing into a system
- check_circleDebug malformed HTML causing rendering issues
- check_circleValidate JSON5 config files with comments
- check_circleCheck JSONL / NDJSON files line by line for streaming APIs
Frequently Asked Questions
What formats can I validate?
We support JSON, XML, YAML, HTML, JSON5, and JSONL (JSON Lines). Each validator provides format-specific error messages.
What kind of errors do the validators detect?
Validators catch syntax errors like missing commas, unclosed brackets, incorrect indentation, illegal characters, and structural issues specific to each format.
Do validators check schema or just syntax?
Our validators check syntax and well-formedness. For JSON Schema or XML Schema (XSD) validation, additional schema-aware tools would be needed.
Can I validate large files?
Yes. Validation runs entirely in your browser. Large files are supported — performance depends on your device and browser.
Developer Insights
From the Blog
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