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YAML Checker Online

Check YAML syntax online: catch indentation errors, tabs, and common mistakes. Validate, format, and convert YAML to JSON locally in your browser (no upload).

Local-only: your YAML stays in your browser. Uses the local js-yaml parser with the JSON schema. Checks syntax, not application-specific requirements.
Tip: YAML forbids tabs for indentation—use spaces.

    

  


  

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            Privacy: runs locally in your browser. No uploads, no tracking scripts.
          

        

      


      

      
How to use

      
Paste your YAML, then choose what you want to do.
  1. Validate to check structure, indentation, and tabs.
  2. To JSON to view the parsed result (useful to verify lists vs objects).
  3. Format YAML to re-dump a normalized YAML (basic subset only).
  4. Fix any reported line number issues and re-run.

      


    

      
FAQ

    
Does this YAML checker support full YAML 1.2?
No—it's a fast subset parser meant for common configs (mappings, lists, scalars). Advanced features like anchors/aliases, tags, merges, and flow collections may be flagged as warnings or treated as plain text.
Why does YAML break so often on indentation?
YAML uses indentation to define structure, so one extra/missing space can move a key into a different level. This tool reports line numbers for unexpected or inconsistent indentation.
Are tabs allowed in YAML?
No—tabs for indentation are invalid in YAML. Use spaces only (commonly 2 spaces per level).
Can I convert YAML to JSON here?
Yes—click To JSON. Conversion works for the supported subset; complex YAML features may not convert as expected.
Will my YAML be uploaded or stored?
No. The tool runs locally in your browser and does not send network requests.
Does the formatter keep comments and original formatting?
No—the formatter re-dumps the parsed structure, so comments and some stylistic choices are not preserved.
Why do I see a duplicate key warning?
YAML mappings can contain duplicate keys, but most tooling treats the last value as the winner. The checker warns because it often indicates a mistake.


    


    
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