What is YAML and why validate it?

YAML (YAML Ain't Markup Language) is a human-friendly data serialization format widely used for configuration files — Docker Compose, GitHub Actions, Kubernetes, Ansible, and many more. Even a single space or missing colon can break a YAML file, making a validator essential before deploying config changes.

What are the most common YAML syntax errors?

The most common YAML errors are: mixing tabs and spaces for indentation (YAML requires spaces only), missing colons after keys, unquoted strings containing special characters like colons or hash marks, duplicate keys in the same mapping, and incorrect list indentation. This tool shows the exact line and column of each error.

What is the difference between YAML and JSON?

YAML is a superset of JSON — all valid JSON is valid YAML. YAML is more human-readable with its whitespace syntax, supports comments using #, and requires less punctuation. JSON is more universal for APIs. YAML is preferred for configuration files that humans read and edit regularly.

Can I use tabs for indentation in YAML?

No — this is one of the most frequent YAML mistakes. The YAML specification explicitly prohibits tab characters for indentation. You must use spaces (2 spaces per level is the standard convention). This validator will immediately flag tab-indentation errors with the exact location.

Does YAML support comments?

Yes. YAML supports single-line comments using the # character, both as full lines and inline after a value. For example: # This is a comment, or key: value # inline comment. This is a major advantage over JSON, which has no comment support.

YAML Validator

Validate and format YAML syntax online. Instantly detect errors and pretty-print valid YAML with proper indentation.

YAML Input

Formatted Output

How to Use

Validate and format YAML syntax online. Instantly detect errors and pretty-print valid YAML with proper indentation.

1Paste your YAML content into the left input panel, or click 'Load Example' to start with a sample YAML structure containing strings, numbers, booleans, and nested objects.
2Validation runs automatically as you type — no submit button needed. Watch the status badge in the top-right of the input panel.
3If your YAML is valid, the formatted output with consistent 2-space indentation appears in the right panel instantly.
4If there is a syntax error, the right panel shows the error message with the exact line and column number so you can fix it quickly.
5Once your YAML is valid, click 'Copy' to copy the formatted output to your clipboard. Use 'Reset' to start fresh with a blank editor.

Key Features

Real-time validation — errors detected instantly as you type, no submit button needed
Pretty-print output — valid YAML is automatically formatted with 2-space indentation
Precise error messages — line and column numbers for every syntax error
Load example — one-click sample YAML to get started immediately
Powered by the official yaml npm package — the same parser used in production tools

Frequently Asked Questions

Learn More

YAML Validator Guide — Fix Common YAML Errors