YAML Formatter
Validate and format YAML configuration files
About YAML Formatter
YAML (YAML Ain't Markup Language) is the configuration file format used by Docker, Kubernetes, GitHub Actions, Ansible and hundreds of other DevOps tools. A single indentation error can break an entire deployment. This free YAML Formatter validates your YAML for tab characters, odd indentation, and large indentation jumps — then normalizes it to clean 2-space indented output ready for your CI/CD pipeline.
How to Use YAML Formatter
- 1Paste your YAML content into the input area, or click "Load Sample" to see an example.
- 2Click "Format & Validate YAML" to normalize indentation and check for common errors.
- 3Any issues (tab indentation, odd spaces, large indent jumps) are highlighted with line numbers.
- 4Copy the clean formatted YAML output to use in your project.
Common Use Cases
Always use 2-space indentation in YAML — never tabs. Tabs are technically invalid in YAML and cause parsing errors in many tools including Docker, Kubernetes and GitHub Actions.
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Frequently Asked Questions
Why does YAML not allow tabs?
The YAML 1.1 and 1.2 specifications explicitly forbid tab characters for indentation. Tabs are invisible and their display width varies by editor, making alignment unreliable. YAML parsers in Python (PyYAML), Go, Docker and Kubernetes all reject YAML files with tab indentation.
What is the difference between YAML and JSON?
YAML is a superset of JSON — all valid JSON is valid YAML. YAML uses indentation instead of braces and brackets, supports comments (# comment), and has cleaner syntax for human-edited config files. JSON is stricter and better for machine-to-machine data exchange. YAML is preferred for configuration; JSON for APIs.
What are the most common YAML errors?
Common YAML errors include: tabs instead of spaces for indentation, inconsistent indentation levels, missing quotes around strings containing special characters (: { } [ ] , & * # ? | - < > = ! % @ `), duplicate keys in the same mapping, and incorrect list item alignment.
Can I use YAML for GitHub Actions?
Yes. GitHub Actions workflows are written in YAML files stored in .github/workflows/. GitHub uses a specific YAML schema for workflow files. Use 2-space indentation and validate your YAML before committing — a YAML syntax error prevents the workflow from running at all.