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YAML's whitespace-sensitive syntax makes it easy to introduce a subtle formatting error — a stray tab, misaligned indentation, or an unquoted special character. This tool checks pasted YAML for syntax errors, reporting the exact line, and can optionally confirm a list of expected top-level keys are all present.
How it works
The YAML is parsed with symfony/yaml (the same parser many PHP frameworks rely on). If parsing fails, the exact line and error message are reported. If it succeeds and you supplied a comma-separated list of required top-level keys, each is checked against the parsed document's actual keys.
- Enter yAML.
- Enter required top-level keys (comma-separated, optional).
- Click Calculate to see your results.
Examples
A common indentation error
A line indented with an unexpected extra space under a mapping key causes a "colon cannot be used in an unquoted mapping value" error at that exact line — YAML doesn't tolerate inconsistent indentation the way some formats do.
Who should use it
- Debugging a broken CI/CD pipeline, Docker Compose, or application config file.
- Quick sanity-check before committing a YAML file.
Industry applications
- DevOps and CI/CD pipeline configuration
- Application configuration management
Advantages
- Reports the exact line of a syntax error rather than a vague failure.
- Optional lightweight required-key check goes beyond pure syntax validation.
Limitations
- Not a full JSON-Schema-style validator — no type, format, or nested-structure enforcement.
Common mistakes to avoid
- Mixing tabs and spaces for indentation, which YAML doesn't reliably tolerate.
- Leaving a colon-containing value unquoted where YAML would otherwise interpret it as starting a new mapping.
Best practices
- Use a consistent number of spaces (commonly 2) for every indentation level and never mix in tabs.
- Supply your expected top-level keys when checking a config file, to catch a silently-missing required section, not just outright syntax errors.
Tips
- If a config file needs specific sections (like "name" and "version"), list them as required keys here to catch a missing section immediately.