YAML Formatter
Format, validate, and convert YAML. Beautify YAML, convert between YAML and JSON, and catch syntax errors.
Use this as an API
Automate this in your app with a single POST request. Free tier included.
Use this in your AI agent
Connect via MCP and let Claude, Cursor, or VS Code call this tool natively.
YAML formatting rules
YAML uses indentation (spaces only, no tabs) to express hierarchy. Maps use key: value
pairs. Lists prefix items with - . Multi-line strings use | for literal
blocks or > for folded blocks. Consistent indentation (2 or 4 spaces) prevents
parsing errors and keeps files readable across teams.
YAML vs JSON
JSON is strict, unambiguous, and supported everywhere. YAML is more readable for humans, supports comments, and handles complex nested structures with less syntax. Most configuration systems (Kubernetes, GitHub Actions, Docker Compose) prefer YAML. APIs and data interchange prefer JSON. Every valid JSON document is also valid YAML, making conversion straightforward.
Common YAML pitfalls
The "Norway problem": YAML 1.1 interprets bare NO as boolean false. Always
quote strings that could be misinterpreted as booleans, nulls, or numbers. Tab characters
cause parse errors; YAML only allows spaces for indentation. Duplicate keys silently
overwrite earlier values in most parsers.
YAML in production workflows
Kubernetes manifests, Helm charts, CI/CD pipelines, and Infrastructure-as-Code tools all depend on YAML. Formatting YAML consistently avoids merge conflicts and improves code review readability. Use this formatter to normalize indentation before committing. For JSON payloads in your configs, our JSON Formatter handles the JSON side. For validating regex patterns embedded in YAML, use our Regex Tester.
Frequently Asked Questions
- What is YAML?
- YAML (YAML Ain't Markup Language) is a human-readable data serialization format. It uses indentation to represent structure and is commonly used for configuration files in Kubernetes, Docker Compose, GitHub Actions, and Ansible.
- Can I convert JSON to YAML?
- Yes. Switch to the "JSON to YAML" mode, paste valid JSON, and the tool produces the equivalent YAML output. This works because JSON is a subset of YAML.
- Why does my YAML fail to parse?
- Common YAML errors include incorrect indentation (YAML uses spaces, not tabs), missing colons after keys, and unquoted strings that contain special characters like colons or hashes. The error message shows the line number where parsing failed.
- Is my data sent to a server?
- No. All YAML parsing, formatting, and conversion runs in your browser using the js-yaml library. Nothing is transmitted over the network.