✓ YAML Validator
Check YAML syntax with line-number error reporting. Detects tab indentation, malformed keys, unbalanced quotes and brackets, and inconsistent nesting — all in your browser, no upload.
About the YAML Validator
This YAML validator runs entirely in your browser. Paste your YAML and click Validate to scan it for common syntax problems. The validator checks for tabs used as indentation (YAML forbids them), mapping keys that are not followed by a colon and space, unbalanced single and double quotes, unbalanced flow collections ([...] and {...}), and inconsistent indentation that would break nesting. Each problem is reported with its line number so you can jump straight to it.
What is YAML?
YAML ("YAML Ain't Markup Language") is a human-friendly data serialisation format used widely for configuration files, CI/CD pipelines, and data exchange. Its structure comes from indentation, which makes it readable but also strict about whitespace — a single stray tab or misaligned space can make a document invalid.
How to use the validator
- Paste your YAML into the input box.
- Click Validate.
- Read the result panel — valid documents report "Valid YAML"; problems list each issue with its line number.
- Fix the issues in your editor and re-validate.
Frequently asked questions
Does it support all YAML 1.2 features? The validator covers the most common syntax rules. Advanced features such as anchors, aliases, tags, and multi-line folded scalars are tolerated but not deeply parsed.
Why does YAML reject tabs? Indentation in YAML is significant and must be spaces. Tabs make nesting ambiguous, so the spec forbids them for indentation. Use spaces — typically 2 per level.
Is my YAML uploaded? No. All validation happens locally in your browser.