Format YAML Online: Validator & Converter
Format YAML with indentation validation. Convert YAML to JSON and back. Check for syntax errors instantly.
Try the free online tool mentioned in this guide:YAML Formatter & Validator
What is YAML and why format it?
YAML (YAML Ain't Markup Language) is a human-readable data serialization language used widely in configuration files (Kubernetes, Docker Compose, Ansible, CI/CD pipelines). Unlike JSON or XML, YAML uses indentation and minimal punctuation, making it easy to read but strict about whitespace.
YAML errors are almost always indentation mistakes: inconsistent spacing, tabs instead of spaces, or wrong nesting depth. A YAML formatter catches these instantly and either fixes them or shows you exactly where the problem is.
YAML syntax basics
Keys and values — key: value format. No quotes needed for simple strings.
Indentation — Nesting is determined by spaces (typically 2 spaces per level). Mixing tabs and spaces breaks parsing.
Lists — - item syntax for arrays.
Strings — Simple strings don't need quotes. Use quotes for strings with special characters or leading/trailing whitespace.
Multiline strings — Use | for literal blocks or > for folded (wrapped) text.
# Valid YAML
name: Alice
age: 30
tags:
- developer
- security
- devops
config:
debug: true
timeout: 30
# Invalid YAML (mixed indentation, wrong spacing)
name: Alice
age: 30 # <- incorrect indent depth
tags: # <- inconsistent with above
- developerConverting between YAML and JSON
YAML and JSON represent the same data structures (objects, arrays, strings, numbers). MyDevTools YAML Formatter lets you convert between them:
- Paste YAML → see equivalent JSON.
- Paste JSON → see equivalent YAML.
This is useful when integrating YAML-based tools with JSON APIs, or when you need to validate YAML structure by converting it to JSON and back.
Common YAML errors and fixes
"Expected block mapping" or "Bad indentation" — Check that your indentation is consistent (all 2 spaces, no tabs). Each nested level should increase by exactly 2 spaces.
"Cannot read property of undefined" — A required key is missing or misspelled.
Unexpected character or "Bad anchor" — YAML anchors (&ref) and aliases (*ref) have specific syntax — check for typos.
Frequently asked questions
Can I mix tabs and spaces in YAML?
No. YAML does not allow mixing tabs and spaces. Always use spaces (typically 2 per indent level).
What is the difference between YAML and JSON?
YAML is more human-readable with minimal punctuation. JSON is stricter, requires quotes around keys, and works directly in JavaScript. Both represent the same data structures.
Can I convert complex YAML with anchors and aliases to JSON?
Yes, YAML anchors (&ref) and aliases (*ref) resolve to the same object in JSON, producing merged or referenced structures.