BlogHow to Format and Validate JSON Online (and Fix the Most Common Errors)
A practical guide to beautifying, minifying and validating JSON in your browser, plus fixes for trailing commas, single quotes and other common JSON syntax errors.
JSON is everywhere: API responses, config files, logs, browser storage. But raw JSON usually arrives as one long unreadable line, and a single misplaced comma is enough to break a whole request. This guide shows a fast workflow to format, validate and minify JSON without installing anything.
Step 1: Paste and format
Open the JSON Formatter and paste your data into the input box. Click Format and the JSON is re-indented with consistent spacing, so nested objects and arrays become easy to scan.
For large payloads, switch to Tree view. You can collapse branches you don't care about and expand only the part you are debugging.
Step 2: Validate
If the input is not valid JSON, the tool shows a parse error instead of output. The error message points to the position where the parser gave up, which is usually right after the real mistake.
Step 3: Minify before shipping
Formatted JSON is for humans. When you paste JSON into a request body, an environment variable or a URL, click Compress to remove all whitespace.
The 5 most common JSON errors
| Error | Invalid | Valid |
|---|---|---|
| Trailing comma | {"a": 1,} |
{"a": 1} |
| Single quotes | {'a': 'x'} |
{"a": "x"} |
| Unquoted keys | {a: 1} |
{"a": 1} |
| Comments | {"a": 1 // note} |
Remove the comment |
undefined / NaN |
{"a": undefined} |
{"a": null} |
Most of these come from copying a JavaScript object literal and treating it as JSON. JavaScript is more permissive; JSON is not.
Is it safe to paste private data?
The pudone! JSON Formatter parses your data with the browser's built-in JSON engine. Nothing is uploaded to a server, so API tokens or customer records in the payload stay on your device.
Tip: need the same data in another format? Use YAML โ JSON for config files or CSV โ JSON for spreadsheets.