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YAML Checker Online

Validate YAML quickly in your browser. This checker focuses on the most common YAML issues (indentation, tabs, list/mapping structure) and can also format YAML (basic subset) or convert it to JSON for debugging.

Category: Developer · URL: /tools/yaml-checker-online.html
Local-only: your YAML stays in your browser. Supports a practical YAML subset (mappings, lists, scalars). Complex YAML features (anchors/aliases, advanced tags, flow collections) may be treated as plain text.
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.

      

        Keywords this page targets (natural cluster): yaml checker online, yaml validator online, yaml lint online, validate yaml, check yaml indentation, yaml tabs error, yaml syntax checker, yaml to json online, format yaml online, yaml parser online, yaml validator tool, yaml linting tool, yaml validate kubernetes manifest, docker compose yaml checker, github actions yaml validator, ansible yaml checker, k8s yaml validation, yaml list mapping validator, fix yaml indentation, yaml duplicate keys check
      

      

        Secondary intents covered: Validate YAML syntax and pinpoint the line that breaks parsing, Detect tabs and inconsistent indentation in YAML, Convert a YAML config into JSON to debug structure, Format/normalize YAML indentation for readability, Check common CI/CD YAML files (GitHub Actions, pipelines) for basic structure issues, Verify Kubernetes/Helm-like YAML manifests for indentation/list mistakes (basic checks), Find duplicate keys in mappings (warn), Copy cleaned output back into an editor quickly
      

    


    

      
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.