Tools · Developer Tools
YAML Formatter, Validator & Viewer
Format, validate, search, and explore YAML in this browser. Duplicate keys are reported instead of dropped.
This YAML is large. Highlighting is reduced so the tab stays responsive.
Formatting, validation, and the tree run in this browser. YAML tags that construct objects are rejected. Duplicate keys are reported with a line number. YAML is not uploaded. YAML↔JSON reuses the Universal Data Converter. API: None.
How to format YAML
- Paste YAML or upload a .yaml, .yml, or .txt file from this device.
- Format or validate. Duplicate keys such as two NODE_ENV lines are listed with line numbers.
- Open Tree to copy a path, or convert YAML↔JSON with the shared converter.
FAQ
Is my YAML uploaded to a server?
No. Parsing, formatting, validation, and search run in your browser. The file is not uploaded to DevNestro.
What happens if a key appears twice?
Both lines are kept and you see Duplicate key with the line number. The tool does not silently drop NODE_ENV: production after NODE_ENV: development.
Are YAML tags or constructors executed?
No. Tags such as !!python/object are rejected. Only a safe subset of mappings, sequences, and scalars is parsed.
How large a file can I format?
The default import limit is 10 MB. Larger files are rejected rather than truncated.
How do I convert YAML to JSON?
Use YAML to JSON to hand the payload to the Universal Data Converter, or JSON to YAML when the editor holds JSON. This page does not ship a second conversion engine.
Read the original guide: Format YAML without dropping a duplicate key.