YAML Validator — Check YAML Syntax Online Free
Paste your YAML to instantly check if it's valid and locate any syntax errors with exact line numbers.
What is YAML Validation?
YAML validation checks whether a YAML document is syntactically correct — proper indentation, valid key-value pairs, correct use of special characters, and well-formed anchors and aliases. YAML is whitespace-sensitive, making indentation errors one of the most common causes of parse failures. This free validator highlights the exact line of any error, making it fast to fix broken Kubernetes manifests, GitHub Actions workflows, and other YAML configuration files.
Common YAML Syntax Errors
- Inconsistent indentation — mixing tabs and spaces, or uneven indent levels
- Unquoted special characters — colons, brackets, or braces in values that need quoting
- Duplicate keys — the same key appearing twice in a mapping
- Invalid anchor references — referencing an alias before its anchor is defined
- Tabs instead of spaces — YAML does not allow tab characters for indentation
Frequently Asked Questions
Why does YAML fail with correct-looking indentation?
YAML prohibits tab characters for indentation — only spaces are allowed. Many editors insert tabs by default. Check that your file uses spaces only. Also verify that all sibling keys are at the same indent level.
Is my data safe?
Yes. All validation runs entirely in your browser using js-yaml. No data is ever sent to a server.
What is YAML lint?
YAML lint is another term for YAML validation — checking YAML for syntax errors. This tool does the same thing.
Can YAML have comments?
Yes. YAML supports comments using #. Everything from # to the end of the line is ignored by parsers. This is one advantage YAML has over JSON.