toololis
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JSON Formatter

Format, validate & minify JSON in your browser 

  
    
  
  
  
 
 
Free online JSON formatter, validator & minifier
 
 Toololis JSON Formatter is a fast, privacy-first JSON tool that runs entirely in your browser. Format messy JSON into clean, indented output with 2 spaces, 4 spaces, or tabs. Minify formatted JSON into a single line. Validate syntax with clear error messages pointing to the exact line and column.

 
Three actions, one tool
 
     
  • Format — Pretty-print with your chosen indent for readability
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  • Minify — Strip all whitespace for transport or storage
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  • Validate — Check syntax without producing output
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How to use this tool
  1. 1
    Paste your JSON
    Drop raw JSON into the input field. Minified, messy, or indented — all accepted.
  2. 2
    Choose indent size
    Pick 2 spaces (JavaScript default), 4 spaces (Python style), or Tab (old-school).
  3. 3
    Click Format, Minify, or Validate
    Format pretty-prints the JSON. Minify strips all whitespace into one line. Validate just checks if the JSON is syntactically valid.
  4. 4
    Copy the output
    Tap the Copy button in the top-right of the output panel to send the formatted JSON to your clipboard.
 
Common JSON syntax errors
 
     
  • Trailing commas — {a: 1,} fails. JSON does not allow the trailing comma JavaScript accepts.
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  • Single quotes — {'a': 1} fails. Keys and string values must use double quotes.
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  • Unquoted keys — {a: 1} fails. Keys must be strings in double quotes.
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  • Comments — // comment and /* block */ are not valid JSON.
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  • Undefined / NaN — JSON only allows null, not undefined or NaN.
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Who uses this
 
     
  • Backend developers debugging API responses
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  • Frontend developers inspecting payloads from browser DevTools
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  • DevOps engineers validating config files (package.json, tsconfig, k8s manifests)
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  • QA engineers comparing expected vs actual API output
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  • Data analysts cleaning JSON exports before import
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Frequently Asked Questions
How does this JSON Formatter work?
It uses the browser's native JSON.parse() to verify structure and JSON.stringify() with your chosen indent to format the output. All parsing happens in your browser — no server round-trip.
Is my JSON data private?
Yes. Your JSON never leaves your device. There are no API calls, no logging, no analytics tracking of input content. Safe for internal API responses, config files, and sensitive payloads.
Why does my JSON show an error?
Common JSON errors include: trailing commas (not allowed in JSON), single quotes (must be double quotes), unquoted keys, or comments (// and /* */ are not valid JSON). The error message shows the line and column of the problem.
What is the maximum JSON size?
The tool handles JSON up to your browser's memory limits — typically 100 MB+ on desktop, 20–50 MB on mobile. Very large files may briefly freeze the UI during parsing.
Can I minify JSON with this tool?
Yes. Click the Minify button to strip all whitespace and produce a single-line JSON string, ideal for transmission or storage.
What's the difference between Format and Validate?
Format parses and re-serializes with indentation. Validate only parses — it confirms "this is valid JSON" without producing output. Use Validate for quick checks.
 
 
  
 

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 100% Privacy. This tool runs entirely in your browser. Your data is never uploaded to any server.