JSON Tools

JSON Formatter & Validator

Paste messy JSON and get clean, indented output with clear validation errors — free, instant and private. Your data is processed in your browser and never uploaded.

 
 
 
     
 
 

100% in your browser — your data never leaves your device.

 
   
 
How to format and validate JSON
 
     
  1. Paste your JSON into the input box on the left.
    2.  
  2. 
It is parsed and pretty-printed instantly in the output panel; pick an
          indent size if you want.

    3.  
  3. 
If the JSON is invalid, the error message and position appear below so
          you can fix it.

    4.  
  4. Click Copy to put the clean JSON on your clipboard.
    5.  
 
Why format JSON?
 

Minified or hand-edited JSON is hard to read and easy to break. Formatting
        adds consistent indentation and line breaks so the structure is obvious,
        and validating it first catches the missing comma or stray bracket that
        would otherwise crash your app or API call.

 
What the formatter does
 

The formatter parses your JSON using the browser's built-in JSON parser,
        then re-serialises it with your chosen indentation — 2 spaces, 4 spaces,
        or a tab. Because it parses first, it also validates the structure and
        points you to the exact character position of the first error, so invalid
        JSON is quick to diagnose and fix rather than silently passing through.

 
Common JSON errors it catches
 
     
  • Trailing commas — a comma after the last item in an object or array is not allowed in standard JSON.
    •  
  • Single quotes — JSON requires double quotes around both keys and string values; single quotes cause a parse error.
    •  
  • Missing or extra commas — a missing comma between two items, or an extra comma in an unexpected position, breaks the structure.
    •  
  • Unquoted keys — unlike JavaScript object literals, JSON keys must always be quoted strings.
    •  
  • Unbalanced braces or brackets — every opening { or [ must have a matching closing character, in the right order.
    •  
 
Formatter vs minifier
 

Formatting (pretty-printing) makes JSON human-readable by adding indentation
        and line breaks, which is ideal while you are debugging or reviewing a
        response. Minifying does the opposite — it strips all insignificant
        whitespace to produce the smallest valid document for use in production
        or network transfers. If you need to shrink JSON instead of expanding it,
        use the JSON Minifier.

 
Related tools
 
     
  • JSON Minifier — strip whitespace from JSON to get the smallest valid output.
    •  
 
 
 
Frequently asked questions
 
 
 
Is my JSON uploaded to a server?
 
No. Formatting and validation run entirely in your browser with the native JSON parser. Your data never leaves your device.
 
 
How does the validator report errors?
 
If the input is not valid JSON, the parser message is shown below the editor, including the character position where parsing failed, so you can jump straight to the problem.
 
 
Can I choose the indentation?
 
Yes. Pick 2 spaces, 4 spaces or a tab, and the output is re-formatted instantly to match.
 
 
Does formatting change my data?
 
No. Only whitespace and key ordering as written are affected — the values and structure stay exactly the same. Reformatting is lossless.
 
 
Does it just format, or does it also validate?
 
Both. The formatter always parses the input first. If the JSON is invalid, it reports an error with the position; only valid JSON produces formatted output.
 
 
What is the largest file I can format?
 
There is no fixed limit — nothing is uploaded, so the only constraint is your device's available memory. Extremely large files may take a moment to process.
 
 
Does it sort or reorder my keys?
 
No. Key order is preserved exactly as you wrote it. The formatter only adjusts whitespace and indentation.
 
 
Does it accept comments or JSON5?
 
No. It expects strict, standard JSON as defined by the JSON specification. Comments, trailing commas, and unquoted keys are not valid JSON and will be reported as errors.