JSON Formatter & Validator

Check JSON syntax and choose readable indentation or compact output. Formatting preserves the original values and number spelling.

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Preparing your tool…

A visual example

Format JSON without changing large IDs

```
{"id":9007199254740993,"ok":true}
```
Before
This ID exceeds JavaScript’s safe integer range.
```
{
  "id": 9007199254740993,
  "ok": true
}
```
After
Whitespace changes; every digit stays intact.

Formatting improves readability. It must not round your numbers.

Illustrative example. Valid JSON may not match your schema.

How to use it

Paste a JSON document.
Choose indentation or compact output, then format and validate.

{"id":9007199254740993,"ok":true} keeps the exact ID when formatted. If {"ok":true,} is rejected, remove the trailing comma to get {"ok":true}, then run it again. The formatter reports syntax errors; it does not repair them automatically.

Details & limits

100,000 UTF-16 code units; nesting limited to 100 levels. Number spelling, string values and duplicate keys are preserved.

Will large numbers lose precision?

No. The formatter validates JSON syntax without converting numeric tokens into JavaScript numbers. Original numeric spelling and duplicate keys are retained. A valid document is not a schema validation or a guarantee that duplicate keys are meaningful.

Inspect JSON without changing what its values say

Formatting helps you read a response or configuration before using it elsewhere. It changes layout around JSON tokens, not the meaning of your data. A successful result answers the syntax question; you still need to know which fields the receiving system expects.

Check an API response with long identifiers

An identifier such as 9007199254740993 must survive formatting exactly. This formatter retains its numeric spelling, as well as 1.2300 and 1e400, instead of rebuilding them from JavaScript numbers. That does not make the next application's number handling safe: if its contract requires an identifier as a string, confirm that requirement at the data source.

Read a configuration with repeated keys

The input {"mode":"test","mode":"live"} keeps both entries in the same order. Formatting makes them easier to notice but does not choose the correct value or resolve the duplication. Check the consuming application’s rules before changing either entry. Use compact output only when you want the same tokens with less layout whitespace.

Check your result

Compare long IDs, decimal spelling and escaped string content with the source before copying the result onward.
Check required fields, allowed values and duplicate keys against the destination's contract; syntax validation does not do this.
Recheck the displayed input after an oversized paste is rejected: the retained earlier text is not the rejected document.

If something looks wrong

Text copied from code is rejected

Object literals can contain comments, unquoted keys or single-quoted strings that JSON does not allow. Obtain an actual JSON export or correct the specific syntax in the source. Avoid replacing quote characters throughout a document indiscriminately.

Valid JSON is rejected by another service

Inspect that service's field names, types and value rules. Reformatting cannot turn a missing field, an unwanted duplicate or an out-of-range business value into acceptable data.

Before

After