YAML Formatter & Validator
Pretty-print, lint, and validate YAML with configurable indentation and detailed parser errors
Interactive tool
YAML input
No YAML to process
Paste YAML or drop a .yaml/.yml file to format and validate
What is a YAML Formatter & Validator?
A YAML formatter pretty-prints YAML with consistent indentation, key ordering, and quoting. The validator parses YAML 1.2 and surfaces syntax errors with line and column references. Together they keep configuration files clean, predictable, and free of subtle indentation bugs.
How to Use This YAML Formatter
- 1Paste YAML or drop a .yaml/.yml file onto the input area
- 2Choose Format to pretty-print or Validate to only check syntax
- 3Pick indentation: 2 spaces or 4 spaces
- 4Toggle "Sort keys" if you want deterministic key ordering
- 5Review validation status and any errors with line numbers
- 6Copy or download the formatted result
Key features
YAML 1.2 Compliant
Parses and formats YAML 1.2 (the modern standard) using the js-yaml library
Pretty-Print Formatting
Consistent indentation and quoting across the entire document
Syntax Validation
Errors include line and column numbers for fast fixes
Optional Key Sorting
Alphabetize keys for deterministic diffs in version control
Configurable Indentation
2 or 4 space indentation to match your project style
Comment-Free Output
Format produces canonical YAML; comments are dropped so structural diffs are clean
Drop File Support
Drop .yaml or .yml files onto the input for instant processing
100% Private
All processing runs in your browser. Nothing is uploaded
Why Format and Validate YAML?
YAML is everywhere: Kubernetes manifests, GitHub Actions, Docker Compose, Ansible, OpenAPI specs, Helm charts, Rails fixtures. A single misplaced space breaks deployment. A formatter normalizes indentation so diffs are meaningful; a validator catches errors before CI runs and ensures your config is parsable by every consumer.
Common use cases
- Validating Kubernetes manifests before kubectl apply
- Linting GitHub Actions workflows during local edit
- Cleaning up Docker Compose files for review
- Auditing OpenAPI specs against their schemas
- Normalizing Ansible playbooks for consistency
- Preparing Helm chart values for templating
- Cleaning up legacy configuration files for upgrade
- Pre-commit checks in YAML-heavy repositories
Why Comments Are Dropped on Format
YAML comments are not part of the document model. When YAML is parsed and re-serialized, comments do not survive. If you need to preserve comments, format only with caution and use Validate-only when comment preservation matters. For most CI and deploy pipelines, the absence of comments after formatting is desirable.
Indentation Matters in YAML
Unlike JSON, indentation defines structure in YAML. Mixing spaces and tabs, or using inconsistent indentation depths, produces parser errors that can be hard to spot. The formatter enforces a single style, eliminating an entire category of YAML bugs.
Tips & best practices
Use 2 spaces for most projects
YAML community convention is 2 space indentation. Stick with it unless your project explicitly requires 4
Validate before commit
Run Validate-only as a pre-commit step to catch errors before they reach CI
Sort keys for stable diffs
Sorted keys produce deterministic output, making code review easier when YAML structure changes
Beware the Norway problem
YAML 1.1 interprets "no" as false. YAML 1.2 (used here) treats it as a string. Modern parsers vary; quote ambiguous values to be safe
Quote version strings
Values like "1.0" can be parsed as floats. Wrap version strings in quotes to keep them as strings
Privacy & security
This YAML formatter and validator runs entirely in your web browser using the js-yaml library. Your YAML data is never uploaded to any server, stored anywhere, or transmitted. All processing happens locally on your device.
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Frequently Asked Questions
Which YAML version is supported?
The formatter parses YAML 1.2 (the modern standard) using the js-yaml library. YAML 1.1 features like the Norway problem (where "no" was a boolean) are interpreted as strings under YAML 1.2.
Why are my comments missing after formatting?
YAML comments are not part of the document model in standard parsers. When YAML is parsed and re-serialized, comments do not survive. Use Validate-only mode if you need to keep comments intact.
How does the validator pinpoint errors?
When YAML parsing fails, the parser reports a line and column number for the first encountered error. Fix that one and re-run; subsequent errors will surface as you go.
What happens with anchors and aliases?
YAML anchors (&) and aliases (*) are resolved during parsing. The formatter outputs the dereferenced result by default. To disable reference resolution, the source YAML should be reorganized before formatting.
Why are version strings quoted in the output?
Values like 1.0 are parsed as floats by default. The formatter preserves type fidelity, so version-like strings are quoted in the output if they were quoted on input. Quote version strings explicitly to ensure they stay as strings.
Is my YAML uploaded anywhere?
No. The formatter and validator run entirely in your browser using the js-yaml library. Your YAML data is never uploaded, stored, or transmitted to any server.