Format, validate, and minify JSON data directly in your browser — instantly spot syntax errors and get a clean, readable structure.
A JSON formatter is a tool that takes raw JSON (JavaScript Object Notation) data and re-indents it into a readable, properly nested structure, while checking that the syntax follows the JSON specification. This free browser-based JSON formatter and validator lets you format, validate, and minify JSON instantly — all processing happens locally in your browser, so no data is sent to a server.
| Task | Action | Example |
|---|---|---|
| Make messy or single-line JSON readable | Format & Validate | {"a":1,"b":2} → indented, nested output |
| Check whether JSON is syntactically correct | Format & Validate | Invalid syntax is flagged with an error message |
| Reduce JSON size for transmission or storage | Minify | Removes all unnecessary whitespace and line breaks |
| Error | Invalid Example | Fix |
|---|---|---|
| Trailing comma | {"a":1,"b":2,} |
Remove the comma after the last item |
| Unquoted keys | {a:1} |
Wrap keys in double quotes: {"a":1} |
| Single quotes | {'a':1} |
JSON requires double quotes, not single quotes |
| Missing comma between items | {"a":1 "b":2} |
Add a comma between key-value pairs |
| Comments in JSON | {"a":1 // note} |
JSON does not support comments — remove them |
| Undefined or function values | {"a":undefined} |
Use null instead — JSON has no undefined |
| Type | Example |
|---|---|
| String | "hello" |
| Number | 42, 3.14 |
| Boolean | true, false |
| Null | null |
| Object | {"key":"value"} |
| Array | [1,2,3] |
JSON formatting and validation is useful for debugging API responses, cleaning up config files, reviewing webhook payloads, checking data before committing it, and teaching JSON structure. If you're working with URL-encoded data inside a JSON value, use SmartWebHub's URL Encoder & Decoder. For binary representations of values, see the Binary Converter.
Paste raw or minified JSON into the input box above.
Select 2 spaces, 4 spaces, or a tab, depending on your project's style.
The tool checks the syntax and outputs a clean, indented, readable version — or shows exactly where the error is if the JSON is invalid.
A JSON formatter re-indents compact or minified JSON into a readable, nested structure so it's easier to read, edit, and debug.
Paste your JSON into the input box and click Format & Validate. The tool parses it and reports whether the syntax is valid, along with the location of any error.
The most common causes are trailing commas, unquoted keys, single quotes instead of double quotes, or a missing comma between items — see the syntax error table above.
Formatting adds indentation and line breaks for readability. Minifying removes all unnecessary whitespace to reduce file size for transmission or storage.
No. The JSON specification does not support comments; including // or /* */
will make the JSON invalid.
Yes. Keys, string values, and literals like true, false, and
null must be written in the exact case JSON expects — True or
NULL are invalid.
JSON uses a compact key-value syntax based on JavaScript objects, while XML uses nested tags. JSON is generally smaller and faster to parse; XML supports attributes, namespaces, and comments.
No. Formatting, validating, and minifying all run locally in your browser using JavaScript — your data is never uploaded.
Technical reference: RFC 8259 (JSON specification) and json.org.