YAML Validator

Paste or type YAML to instantly validate, format, and detect errors with line numbers.

Keys may be reordered in the formatted output — this is normal behaviour of the YAML serializer and does not affect validity.

Common YAML Mistakes

  • × Tabs instead of spaces — YAML requires spaces for indentation, never tabs.
  • × Inconsistent indentation — nested items must align exactly.
  • × Missing space after colon — key:value is invalid; use key: value.
  • × Unquoted special characters — strings with : # { } should be quoted.

YAML Tips

  • ✓ Multi-document — separate documents with --- on its own line.
  • ✓ Comments — use # for inline or full-line comments.
  • ✓ Multi-line strings — use | (literal) or > (folded) block scalars.
  • ✓ Anchors & aliases — use &anchor and *alias to reuse values.

Frequently Asked Questions

What is YAML?

YAML (YAML Ain't Markup Language) is a human-readable data serialisation format commonly used for configuration files — Docker Compose, Kubernetes, GitHub Actions, and many more.

Why are my keys reordered in the output?

YAML objects are unordered by spec. The js-yaml serialiser may sort or reorder keys — this doesn't change the meaning of the document and the output is still valid YAML.

Does this support multi-document YAML?

Yes. Separate documents with --- on its own line. Each document is validated and formatted individually.

Is my data sent anywhere?

No — all validation happens entirely in your browser using js-yaml. Nothing is sent to any server.