ZenovayTools

YAML Validator

Validate and format YAML syntax. Checks for parse errors, shows line numbers, and optionally converts to JSON for inspection.

How to Use YAML Validator

  1. 1Paste your YAML into the editor.
  2. 2Validation runs automatically — errors show with line numbers.
  3. 3Toggle JSON view to inspect the parsed structure.
  4. 4Copy the formatted or JSON output.
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Frequently Asked Questions

What makes YAML different from JSON?▾
YAML (YAML Ain't Markup Language) is a superset of JSON designed for human readability. Key differences: YAML uses indentation (spaces, not tabs) for structure instead of braces/brackets; strings do not need quotes in most cases; comments are supported with #; multi-line strings are easy with | and >; YAML supports anchors and aliases for reusing values. JSON is a strict subset of YAML — all valid JSON is valid YAML.
What are common YAML syntax errors?▾
Most common YAML errors: mixing tabs and spaces (only spaces allowed), incorrect indentation level, unquoted strings containing special characters (: { } [ ] # & * ? | - < > = ! % @ `), duplicate keys at the same level, unclosed multi-line string blocks, and incorrect boolean parsing (yes/no/on/off are parsed as booleans in YAML 1.1). Always quote strings that start with special characters.
What is the difference between | and > in YAML?▾
Both are block scalar indicators. | (literal block) preserves newlines literally — useful for scripts and code blocks. > (folded block) converts newlines to spaces except for blank lines — useful for long prose. Both support a trailing newline (default), - to strip trailing newlines, or + to keep all trailing newlines. Example: description: > This is a long text that wraps across lines.
What are YAML anchors and aliases?▾
Anchors (&) define a reusable value and aliases (*) reference it. Example: defaults: &defaults timeout: 30 retries: 3. Then production: <<: *defaults env: production. The << key is a merge key — it merges the aliased object into the current one. This reduces repetition in config files, commonly used in GitHub Actions and Docker Compose.
Why is my YAML boolean being parsed as a string?▾
YAML 1.1 treats these as booleans: true/false, yes/no, on/off (and their uppercase variants). YAML 1.2 only treats true/false as booleans. Libraries differ in which spec they follow. If you want a string, always quote it: "yes", "no", "true". This is a common source of bugs in config files — for example, a country code "NO" (Norway) being parsed as false.