JSON Formatter & Validator (Free, Online, Private)
Kamran Liaquat Ali- posted on
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Use this free JSON formatter and validator to beautify, minify and check JSON in one place. Paste an API response, config file or log line, and the tool formats it with clean indentation, points to the exact line and column of any error with a plain-English explanation, and can auto-fix common mistakes such as trailing commas, comments and single quotes. Everything runs in your browser, so your data stays private.
JSON Formatter & Validator
Paste JSON to format, minify or validate it. Errors show the exact line and column with a plain-English fix. Runs in your browser; nothing is uploaded.
Privacy: everything runs in your browser. Your JSON is never sent to a server, so it is safe for API responses and config files. Large numbers keep their exact digits.
Seeing an error you do not understand? Our guide Common JSON Errors and How to Fix Them explains every message this tool shows, with before-and-after examples.
How to Use the JSON Formatter
- Paste your JSON into the input box, open a
.jsonfile, or click Sample to try it. - Click Format (or press Ctrl+Enter) to beautify it with 2 spaces, 4 spaces or tabs.
- Click Minify to remove all whitespace for smaller payloads.
- Click Validate to check the JSON without changing it.
- If there is an error, read the message, click Go to error to jump to the exact spot, or try Auto-fix.
- Switch to Tree view to explore nested objects and arrays, then copy or download the result.
Features
| Feature | What it does |
|---|---|
| Format and minify | Beautify with 2 spaces, 4 spaces or tabs, or compress to a single line |
| Strict validation | Checks against the JSON standard (RFC 8259) and reports the exact line and column |
| Plain-English errors | Explains problems such as trailing commas, missing commas, single quotes, comments, leading zeros and unclosed brackets |
| Auto-fix | Removes comments and trailing commas, converts single quotes, quotes unquoted keys and replaces True, False, None, undefined and NaN |
| Duplicate key warning | Flags keys that appear twice in the same object, which most parsers silently overwrite |
| Exact numbers | Keeps large IDs such as 9007199254740993 and values like 1.10 exactly as written |
| Sort keys | Orders object keys A to Z, which makes two JSON files easier to compare |
| Tree view and stats | Shows the structure, size, number of objects, arrays, keys and nesting depth |
Why Exact Numbers Matter
Many online formatters run your text through JavaScript’s JSON.parse, which stores every number as a 64-bit floating-point value. Integers larger than 9,007,199,254,740,991 lose precision, so an order ID like 9007199254740993 quietly becomes 9007199254740992. This tool uses its own parser and prints numbers exactly as they appear, so IDs, prices and timestamps are never changed while formatting.
Common Errors It Catches
| Problem | Example | Fix |
|---|---|---|
| Trailing comma | {"a": 1,} | Remove the last comma |
| Single quotes | {'a': 1} | Use double quotes |
| Unquoted key | {a: 1} | Write {"a": 1} |
| Comment | // note | Delete it; JSON has no comments |
| Missing comma | {"a": 1 "b": 2} | Add a comma between properties |
| Python values | True, None | Use true and null |
| Leading zero | {"n": 07} | Write 7, or use a string for codes |
Each of these is explained in detail in common JSON errors and how to fix them.
Privacy
API responses and config files often contain tokens, emails or customer data. This JSON formatter processes everything locally in your browser: nothing is uploaded, stored or logged. You can even use it offline once the page has loaded.
Frequently Asked Questions
Is this JSON formatter free?
Yes. It is free with no sign-up and no limits beyond what your browser can handle; files up to 10 MB work well.
Is my JSON uploaded to a server?
No. Formatting, validation and auto-fix all run in your browser.
What is the difference between formatting and validating?
Validating checks that the text follows the JSON rules. Formatting validates it first and then rewrites it with consistent indentation. Invalid JSON cannot be formatted until the error is fixed.
Can it fix my JSON automatically?
It can fix common, unambiguous problems: comments, trailing commas, single quotes, unquoted keys and invalid literals like True or undefined. Missing commas or brackets need a human decision, so the tool points to them instead.
Does JSON allow comments?
No. Standard JSON has no comment syntax. Some tools accept JSONC (JSON with comments), but APIs and most parsers reject it.
Why does sorting keys help?
Sorted keys make it easier to compare two versions of a config or API response, because the same properties appear in the same order.
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