ToolsDiary
Developer tool

JSON Formatter & Validator

Validate, pretty-print or minify JSON directly in the browser.

Free to use No sign-up Browser-based
Tool workspace

Use the tool

Privacy-conscious: this tool runs in your browser where practical, so your working input stays on your device unless the page explicitly says otherwise.

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Learn the workflow

JSON Formatting and Validation: How to Find Errors Without Guessing

Learn the difference between formatting and validation, diagnose common JSON syntax errors, and verify data before using it in an API or application.

Read guide →

What this tool does

Paste JSON to check whether it is valid, format it with readable indentation or minify it for compact transfer. Parsing happens locally and clear error messages help identify the approximate failure position.

JSON syntax is strict: keys and string values use double quotes, commas cannot be placed arbitrarily and braces or brackets must balance. A formatter can reveal structure quickly, but it does not confirm that the data follows a particular application schema.

Useful for

  • Format API responses and configuration snippets.
  • Catch syntax mistakes before saving a JSON file.
  • Minify valid JSON for compact storage or transfer.

How to use it

  1. Paste the JSON text.
  2. Choose Validate, Format or Minify.
  3. If parsing fails, review the error message and nearby text.
  4. Copy the corrected output after validation succeeds.

Worked examples

Quotes must be valid JSON

Input{'name':'Amina'}

Result{"name":"Amina"}

JSON requires double quotes around object keys and string values.

Trailing comma

Input{"name":"Amina",}

Result{"name":"Amina"}

A trailing comma before the closing brace makes standard JSON invalid.

Common mistakes to avoid

  • Using single quotes because the text looks similar to a JavaScript object literal.
  • Leaving a trailing comma after the final array item or object property.
  • Expecting syntax validation to confirm required fields, data types or other JSON Schema rules.

Practical tips

  • Do not paste secrets, private keys or production credentials into any online tool; this tool is local, but good credential hygiene still matters.
  • Validation confirms JSON syntax, not business rules.
  • Large files may be limited by your browser memory.
  • Keep source control as the authoritative copy of configuration files.

Frequently asked questions

Does the formatter change values?

It parses and serializes valid JSON, which changes whitespace but preserves JSON data values.

Can it validate JSON Schema?

No. It validates JSON syntax only.

Is my JSON uploaded?

No. The formatter runs in your browser and does not send the input to ToolsDiary.