Online YAML Validator [2025]

YAML stands for YAML Ain't Markup Language (a recursive acronym). It's a human-friendly data serialization standard for all programming languages. YAML is commonly used for configuration files (like in Docker Compose or Kubernetes), inter-process messaging, and data storage or transmission.

Its primary design goal is human readability. It uses indentation (spaces, not tabs) to denote structure, making files look clean and easy to understand at a glance. Key features include key-value pairs (mappings), lists (sequences), scalars (strings, numbers, booleans), anchors/aliases for reusing data, and comments.

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  Catch Indentation Errors:

  YAML relies heavily on indentation. Even a single misplaced space can break the structure and cause parsing errors. Validation quickly finds these issues.

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  Prevent Application Failures:

  Incorrect configuration in files like Kubernetes manifests or application settings will lead to deployment failures or runtime problems. Validation is crucial.

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  Ensure Correct Data Structure:

  Validation confirms that your mappings, sequences, and scalars are syntactically correct according to the YAML specification.

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  Improve Debugging:

  When systems aren't behaving as expected due to configuration, validating the YAML files is often the first and fastest debugging step.

• Incorrect indentation (mixing spaces and tabs, inconsistent space count).
• Missing colon (`:`) after a mapping key: `key value` instead of `key: value`.
• Incorrect list/sequence syntax: Forgetting the hyphen (`-`) or using inconsistent indentation for list items.
• Unescaped special characters within strings (e.g., a colon `:` in an unquoted string).
• Duplicated keys within the same mapping.
• Invalid anchor (`&`) or alias (`*`) usage.
• Malformed multi-line strings.

Our validator uses the `js-yaml` library, which adheres to the YAML 1.2 specification, to help you identify these and other syntax issues.