YAML Validator
Validate YAML syntax and see parsed output instantly. Detect indentation errors, invalid mappings, and duplicate keys. Free online tool, 100% in your browser.
Reference
What is YAML?
YAML (YAML Ain't Markup Language) is a human-friendly data serialization format widely used for configuration files. It powers Docker Compose (docker-compose.yml), Kubernetes manifests, GitHub Actions workflows, Ansible playbooks, CI/CD pipelines (GitLab CI, CircleCI), and application config files (Rails, Spring Boot). YAML uses indentation instead of braces or brackets to represent structure, making it clean and readable but sensitive to whitespace errors. This validator parses your YAML and reports syntax errors with line numbers to help you pinpoint issues quickly.
YAML syntax essentials
YAML uses indentation (spaces only, never tabs) to denote nesting. Key-value pairs use key: value syntax. Lists use - item prefix. Common errors: mixing tabs and spaces (always use spaces), inconsistent indentation depth, missing space after :, unquoted strings containing special characters (:, #, [, ], {, }), and duplicate keys in the same mapping. Strings with special characters should be wrapped in single or double quotes. Multi-line strings use | (literal) or > (folded) block scalars.
Privacy
All validation runs 100% in your browser. No YAML data is sent to any server.