YAML Validator & Formatter
Validate YAML syntax and format it cleanly. Instantly catch indentation errors, tab characters, and malformed values in Docker, Kubernetes, GitHub Actions, and other YAML configs.
YAML gotchas: No tabs (spaces only) · Consistent indentation
throughout · String values with colons need quotes · Boolean values:
true/false (not Yes/No in strict mode)
Frequently Asked Questions
Why is YAML so easy to break? +
YAML is whitespace-sensitive — indentation with inconsistent spaces (or accidentally using tabs) completely changes how the document parses. A 2-space indent and a 3-space indent create different structures. This is why copy-pasting YAML from different sources often breaks things. The validator above pinpoints the exact line with the problem.
Does YAML allow tabs for indentation? +
No. The YAML spec explicitly forbids tab characters for indentation — only spaces are allowed. This is one of the most common sources of YAML errors, especially for developers who use tab-based editors. Use spaces only, and configure your editor to insert spaces when you press Tab in .yml files.
What's the difference between YAML and JSON? +
YAML is a superset of JSON — valid JSON is valid YAML. YAML is more human-readable with less punctuation (no quotes for strings, no commas, no braces required). YAML supports comments with #, multiline strings, and anchors/aliases for DRY configs. JSON is simpler and better for machine-to-machine communication.
Why does my GitHub Actions workflow fail even though the YAML looks correct? +
GitHub Actions uses YAML but also has its own schema requirements (specific keys, required fields, value types). Even valid YAML can fail if the keys are wrong or the structure doesn't match GitHub's expected schema. After validating YAML syntax here, use the GitHub Actions schema linter in your editor (VS Code has an extension) to catch schema-level errors.