Prevent Deployment Failures
Invalid YAML can cause Docker Compose, Kubernetes, or CI/CD pipeline failures. Validating before deployment catches syntax errors early, saving debugging time and preventing production outages.
YAML Validator - Check YAML Syntax Online
Validate YAML syntax, find indentation errors, and ensure your configuration files are well-formed. Free, fast, and secure.
Size:
14
Paste your YAML here to validate syntax...
OutputEMPTY
Formatted output will appear here...
How to Validate YAML
1
Paste Your YAML
Copy your YAML configuration and paste it into the input editor.
2
Click Format or Validate
Click "Format" to check syntax. Errors are highlighted with line numbers.
3
Fix Errors
Review error messages and fix issues. Re-validate until your YAML is correct.
Common YAML Errors & How to Fix Them
✗ Inconsistent Indentation
Invalid:
database: host: localhost port: 5432 # wrong indent
Valid:
database: host: localhost port: 5432
✗ Tabs Instead of Spaces
YAML only accepts spaces for indentation, not tabs. Configure your editor to use spaces (typically 2) and enable "show whitespace" to identify tabs.
✗ Special Characters Not Quoted
Invalid:
message: Error: Something failed url: http://example.com
Valid:
message: "Error: Something failed" url: "http://example.com"
✗ Missing Space After Colon
Invalid:
name:value # no space
Valid:
name: value # space after colon
Why Validate YAML?
Catch Indentation Issues
YAML's whitespace-sensitivity makes indentation errors hard to spot visually. A single wrong space can completely change the meaning or break the file. Our validator catches these subtle issues instantly.
Clear Error Messages
Instead of cryptic parser errors, we provide clear messages explaining what's wrong and where. Error line numbers help you quickly locate and fix issues in large configuration files.
100% Client-Side
All validation happens in your browser. Your YAML configurations, which often contain passwords, API keys, and sensitive settings, are never uploaded to any server.
YAML Best Practices
✓Use 2-space indentation
Most YAML tools and linters expect 2 spaces. It's the de facto standard.
✓Quote strings with special chars
Always quote strings containing :, #, -, or starting with *, @, &.
✓Use explicit typing when needed
Force types with !!str, !!int, !!bool if automatic detection causes issues.
✓Add comments
YAML supports # comments. Use them to document complex configurations.
YAML-Specific Edge Cases
Indentation Is Structural
One missing space can change the document tree entirely. If validation fails, inspect indentation first before assuming the data itself is wrong.
Ambiguous Scalars
Values like yes, no, on, off, and date-like strings may be interpreted differently depending on the parser and YAML version. Quote them when you need exact string values.
List Items vs Nested Objects
Dashes start list items, but alignment determines whether the item is a sibling or a child. Misplaced dashes are one of the most common causes of confusing validation failures.
Anchors and Aliases
YAML anchors and aliases are powerful, but they can make configs harder to reason about. Validate the expanded structure if your tooling depends on predictable output.
YAML Validation Checklist
- Check indentation and nesting before everything else.
- Quote ambiguous scalars when exact strings matter.
- Inspect anchors, aliases, and merged values carefully.
- Use the YAML to JSON converter when you need strict machine parsing.
- Keep comments in the YAML source if they are part of the documentation.
Frequently Asked Questions
Why is indentation so important in YAML?
YAML uses indentation to represent structure (unlike JSON which uses braces). The level of indentation determines parent-child relationships between elements. Inconsistent indentation breaks this structure and causes parsing errors.
Can I use tabs in YAML?
No! YAML explicitly forbids tabs for indentation. You must use spaces only. Configure your editor to convert tabs to spaces (typically 2) when editing YAML files. Our validator will catch any tab characters in your YAML.
What are YAML anchors and aliases?
Anchors (&name) let you mark a value for later reuse. Aliases (*name) reference that value elsewhere. This prevents repetition:
defaults: &defaults
timeout: 30
database: *defaultsHow do I include multiple documents in one YAML file?
Use --- to separate multiple YAML documents in one file. This is commonly used in Kubernetes to define multiple resources in a single file. Each document is parsed independently.