What is a YAML validator?
A YAML validator checks whether a text document conforms to YAML syntax rules well enough to be parsed into a data structure. YAML — YAML Ain't Markup Language — is the default format for countless configuration systems: Kubernetes manifests, Docker Compose files, GitHub Actions workflows, Ansible playbooks, CI/CD pipelines, and cloud deployment templates. A single indentation mistake in any of these can prevent an entire deployment.
This validator parses your document in the browser and reports either a success summary describing the top-level structure, or a failure with the parser's message and line number. That immediate feedback turns opaque "yaml: line 42: did not find expected key" log messages into something you can fix in seconds.
How to use the YAML validator
- Paste your YAML into the text area — a config snippet, a full manifest, or a CI workflow file.
- Click Validate YAML. Results appear above the button.
- If valid, a green banner confirms success and summarizes what was parsed — for example, an object with 6 keys or an array with 12 items.
- If invalid, a red banner shows the error message and line number. Jump to that line in your editor, fix the issue, and validate again.
Common YAML mistakes
Indentation errors
YAML uses spaces (not tabs) to express nesting. Mixing 2-space and 4-space indentation in the same file, or accidentally dedenting a child key, is the most frequent cause of validation failures.
Trailing commas in lists
Unlike JSON, YAML list syntax does not use commas between items. Writing - item1, item2 as a single list entry is valid, but a trailing comma after the last key in a flow mapping is not.
Unquoted special characters
Values containing colons, hash signs, or leading exclamation marks may need quoting. When in doubt, wrap the value in double quotes.
Validation vs. conversion
Validation answers "is this well-formed YAML?" Conversion tools like the YAML to JSON Converter perform the same parse step and then transform the result. If conversion fails, run validation first to isolate the syntax problem before worrying about output format. Once valid, you can convert to JSON for systems that do not accept YAML natively.
Practical tips
- Validate edited config files before committing — a broken YAML file in main can block every pipeline that depends on it.
- Configure your editor to show whitespace and indent YAML with spaces only; most validation errors disappear when indentation is visible.
- Pair this tool with the JSON Validator when migrating configs between formats.
- For XML-based configs, use the XML Validator instead.