YAML Validator Online
Validate the syntax of your YAML files. Detect indentation and formatting errors instantly.
What is YAML and Why Do You Need to Validate It?
YAML (YAML Ain't Markup Language) is a data serialization format designed to be readable by both humans and machines. It has become the de facto standard for configuration files in the DevOps and cloud-native ecosystem, being used by Docker Compose, Kubernetes, Ansible, GitHub Actions, CI/CD pipelines, and many other modern tools. Its indentation-based syntax makes it visually clean, but that same reliance on indentation is the most common source of errors.
Unlike JSON, which uses curly braces and brackets to define structure, YAML uses indentation (spaces, never tabs) to represent data hierarchy. A single extra or missing space can completely change the meaning of the document or cause hard-to-detect parsing errors. That's why a YAML validator is essential for catching problems before deploying configurations to production.
Common YAML Errors
Using tabs: YAML does not allow tabs for indentation. Only spaces are permitted. This is the most frequent error and can be hard to spot visually in some editors.
Inconsistent indentation: Mixing different indentation levels (e.g., 2 spaces at one level and 4 at another) can cause parsing errors or incorrect structure interpretations.
Colon without space: After the colon in a key-value pair, there must be at least one space. key:value is invalid, while key: value is correct.
YAML vs JSON
YAML is a superset of JSON, meaning any valid JSON document is also valid YAML. However, YAML offers additional features such as comments (with #), anchors and aliases for reusing values, multiple documents separated by ---, and richer data types like native dates and timestamps. While JSON is preferred for APIs due to its simplicity and parsing speed, YAML dominates in configuration due to its superior readability.
Frequently Asked Questions
Why doesn't YAML allow tabs?
YAML prohibits tabs because different editors and systems interpret them differently (some as 2 spaces, others as 4 or 8). This would cause inconsistencies in indentation interpretation. Using spaces ensures the document looks and parses the same in any environment.
How do I represent multiline strings in YAML?
YAML offers two operators: the pipe | preserves line breaks (literal block), and the greater-than sign > converts them to spaces (folded block). Both are useful for including long text, scripts, or embedded configurations within a YAML file.
Does YAML support comments?
Yes, YAML supports comments using the # symbol. Everything following the # on a line is ignored during parsing. Comments can go on their own line or at the end of a code line. This is a significant advantage over JSON, which doesn't allow comments.
What is the correct file extension for YAML files?
The official extensions are .yaml and .yml. The YAML specification recommends .yaml when possible, but .yml is equally valid and very common, especially in environments where three-character extensions were the norm (like older Windows systems).