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JSON Formatter

Validate, format, minify, and explore JSON. Syntax highlighting and error detection.

Indent:
InputN/A
Output

Output will appear here

A JSON formatter is a tool that takes raw, minified, or improperly indented JSON text and reformats it with consistent indentation, line breaks, and syntax highlighting so it is easy to read and debug. Developers use JSON formatters when inspecting API responses, debugging configuration files, or sharing structured data with colleagues. AlteredIdea's JSON formatter runs entirely in your browser: your data never leaves your device.

Format JSON online: instant pretty print with syntax highlighting

AlteredIdea's JSON Formatter transforms minified or malformed JSON into clean, readable output with consistent indentation and color-coded syntax highlighting. Paste any API response, configuration file, or database export and get a formatted result in milliseconds: no account, no upload, no waiting.

Because formatting runs entirely in your browser, your JSON data stays completely private. There is no network request, no server-side processing, and no analytics on the content you paste. It is the safest way to work with sensitive payloads like authentication tokens, user records, or internal configuration values.

Beyond prettifying, the tool doubles as a JSON validator. If your input contains a syntax error: a trailing comma, an unquoted key, or mismatched brackets: the error panel highlights exactly what went wrong with the native browser error message, making debugging fast even for long, deeply nested structures.

How to format JSON online: step by step

  1. 1
    Paste your JSON
    Copy any JSON string: an API response, a config file, a database export: and paste it into the Input panel.
  2. 2
    Choose a mode
    Select Format to indent and highlight, Minify to collapse whitespace, or Validate to check syntax without changing structure.
  3. 3
    Pick an indent size
    Choose 2 spaces, 4 spaces, or tabs depending on your project's code style.
  4. 4
    Review the output
    The Output panel shows your result with color-coded keys, strings, numbers, and booleans for quick scanning.
  5. 5
    Copy and use
    Click Copy to send the result to your clipboard, then paste it wherever you need it.

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Frequently Asked Questions

Is my JSON data sent to a server?
No. All formatting and validation runs directly in your browser using JavaScript's built-in JSON.parse and JSON.stringify. Your data never leaves your device.
What does JSON formatting actually do?
The formatter parses your raw JSON text and re-serializes it with consistent indentation, line breaks, and sorted keys (if enabled). This makes nested structures visually scannable.
Why does validation fail on valid-looking JSON?
JSON is stricter than JavaScript object literals. Common issues include trailing commas, single-quoted strings, unquoted keys, and comments: none of which are valid JSON.
What is the difference between Format and Minify?
Format adds whitespace and indentation to improve readability. Minify does the opposite: it strips all unnecessary whitespace to reduce file size, which is useful for production APIs and storage.
Can I format very large JSON files?
Yes, but browser performance varies. Files under a few megabytes format instantly. For larger files, consider splitting the JSON or using a CLI tool like jq.
Does the formatter support JSON5 or JSONC?
No. This tool strictly parses standard JSON per the ECMA-404 specification. JSON5 (with comments and trailing commas) is not supported.
What do the stats at the bottom mean?
Total Keys counts every property across all nested objects. Max Depth shows how many levels of nesting exist. Original/Result Size shows byte counts before and after formatting.
Can I use this on a phone or tablet?
Yes. The layout is fully responsive and the tool works on any modern mobile browser without any install.
Is there a way to sort JSON keys alphabetically?
The formatter preserves key order as parsed. For alphabetical sorting, use the JSON Analyzer tool which offers key sorting as an option.
What browsers are supported?
All modern browsers are supported: Chrome, Firefox, Safari, Edge, and their mobile counterparts. No polyfills or plugins are required.

AlteredIdea vs alternatives

vs JSONLint: JSONLint sends your data to their server for validation. AlteredIdea formats and validates entirely client-side, so sensitive payloads never leave your browser.

vs VS Code extensions: Extensions require you to open VS Code, create a file, and install a plugin. AlteredIdea works instantly in any browser tab: no install, no project setup.

vs paid tools: Completely free with no account, no trial period, and no rate limits. Format as much JSON as you need, as often as you need.

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