Free JSON Formatter, Validator & Repair Tool — Format, Fix & Sort JSON Online (2026)

JSON Formatting, Validation & Repair — Complete Guide (2026)

What the Fix Mode Automatically Repairs

How to Use This JSON Formatter — Step by Step

1. 1
   Paste or type your JSON into the left "Input JSON" panel. You can also click Load Sample to try a pre-built example.
2. 2
   Choose a mode using the tab buttons: Format to beautify with indent and sort options, Fix to auto-repair errors, or Validate to check syntax only.
3. 3
   View the live result instantly in the right panel — no button click needed. The output updates as you type.
4. 4
   In Fix mode, a green banner lists every repair applied. In Validate mode, a red or green indicator shows validity instantly.
5. 5
   Copy or download the result using the buttons in the output panel header, or use the Copy/Download buttons in the success bar below.

JSON Data Types Reference

6 Most Common JSON Syntax Errors & How to Fix Them

Who Uses a JSON Formatter?

Frequently Asked Questions

• What is JSON and why is it widely used?

  JSON (JavaScript Object Notation) is a lightweight, text-based data format used to transmit data between servers and web applications. It is widely used because it is human-readable, easy to parse in virtually every programming language, and natively supported by JavaScript. APIs, configuration files, databases like MongoDB, and mobile apps all rely on JSON for data exchange.

• What is the difference between formatting and validating JSON?

  Formatting (or beautifying) JSON adds indentation and line breaks to make the structure readable. Validating JSON checks whether the text is syntactically correct — that all braces are matched, keys are in double quotes, commas are in the right places, and values are valid JSON types. You can format already-valid JSON, but you cannot format invalid JSON until the syntax errors are corrected.

• What does the Fix mode do?

  The Fix mode auto-repairs the 6 most common JSON errors automatically: JavaScript-style comments (// and /* */), trailing commas before } or ], single-quoted strings and keys, unquoted object keys, and undefined/NaN/Infinity values replaced with null. After applying all detectable repairs, the output is formatted as valid, pretty-printed JSON with a list of every change that was made.

• Why does my JSON show a 'SyntaxError: Unexpected token' error?

  This error usually means the JSON parser encountered a character it did not expect. Common causes include: single quotes instead of double quotes around strings or keys, a trailing comma after the last item in an array or object, an unescaped backslash or control character inside a string value, JavaScript-style comments (// or /* */), or missing commas between key-value pairs. Use our Fix mode to auto-repair many of these issues, or Validate mode to see the exact error location.

• What are the most common JSON syntax errors?

  The five most common JSON syntax errors are: (1) trailing commas — a comma after the last element in an array or object; (2) single quotes instead of double quotes; (3) unquoted keys — JSON requires all object keys to be double-quoted strings; (4) comments — JSON does not support // or /* */ comments; (5) undefined or NaN values — JSON only supports null, not JavaScript's undefined or NaN. Our Fix mode can repair all five automatically.

• Is JSON5 or JSONC (JSON with comments) supported?

  This tool uses the standard JSON specification (RFC 8259) and validates with JSON.parse(). JSON5 (which allows single quotes, comments, trailing commas) and JSONC (JSON with comments, used by VS Code) are not standard JSON and will be flagged as invalid by this tool. However, the Fix mode can strip comments and trailing commas to convert JSON5/JSONC into standard JSON automatically.

• What does Sort Keys A-Z do?

  The Sort Keys A-Z toggle in Format mode recursively sorts all object keys alphabetically throughout the entire JSON structure. This makes it easy to compare two JSON objects, spot missing fields, and produce deterministic output for version control diffs. Array order is preserved — only object keys are sorted. The sorting is deep, so nested objects are also sorted.

• Can I format large JSON files in the browser?

  Yes, for most JSON files this tool handles formatting instantly since all processing runs in your browser via JavaScript. Very large files (10 MB+) may take a moment or cause the browser tab to temporarily freeze during parsing. For extremely large JSON datasets (hundreds of MB), a desktop tool like jq (command-line) or a dedicated IDE plugin will perform better.

• How is my JSON data kept private?

  All JSON processing happens entirely inside your browser using JavaScript. Your JSON data is never sent to any server, never stored in a database, and never logged. You can even disconnect from the internet after loading this page and the tool will continue to work. This makes it safe for formatting sensitive data like API keys, personal information, or internal configuration.

• What is the difference between 2-space and 4-space indentation?

  Both are cosmetic choices that do not affect the validity or meaning of JSON. 2-space indentation produces more compact output, preferred in many web projects and by tools like Prettier. 4-space indentation is the default in many editors and is slightly easier to read for deeply nested structures. The JSON specification does not mandate any specific indentation style.

• Can JSON keys be numbers or non-string values?

  No. According to the JSON specification, all object keys must be strings enclosed in double quotes. While JavaScript objects can use numeric or symbol keys, JSON does not allow this. A key like { 1: 'value' } is invalid JSON — it must be written as { "1": "value" } with the key as a quoted string.

• Is this JSON formatter and validator free to use?

  Yes, this JSON Formatter, Validator & Repair Tool is completely free with no usage limits, no account required, and no data collection. Format, fix, and validate as many JSON files as you need. All processing happens in your browser, so your data stays private. Bookmark this page for quick access during your development workflow.