Validate · format · inspect

Format JSON and find syntax errors locally

Validate and pretty-print JSON in the browser with precise parse errors and no upload.

Parser testedReviewed 2026-07-18

JSON input72 characters

Result

Your checked result will appear here.

Standards-basedValidation uses the browser's built-in JSON parser.LocalThe JSON value never leaves this browser tab.Reviewed2026-07-18

Reject the broken branch before formatting the rest

Pretty printing is the final step. The parser first checks that the entire value follows JSON syntax, then serializes the parsed value with two-space indentation.

A raw data stream passing through a validation gate into a nested hierarchy while one broken branch is isolated — Valid structure continues into the hierarchy; malformed input stops at a precise boundary. Original MCXAI artwork.

What happens after you press Format JSON

No repair is applied behind your back. Invalid syntax returns an error instead of guessing what the missing value should be.

1Check the limit
Inputs over 1 MB are rejected before parsing to keep the browser responsive.
2Parse the whole value
Objects, arrays, strings, numbers, booleans and null must all follow JSON grammar.
3Stop on syntax errors
The parser reports the failure instead of producing a partially trusted result.
4Serialize consistently
A valid value is returned with stable two-space indentation for inspection or copying.

One valid fixture, one deliberate failure

Both cases are regression-tested. The displayed output is produced by the same functions used in the workbench.

Compact input

{"project":"MCXAI","checks":["metadata","privacy"],"ready":true}

Formatted output

{
  "project": "MCXAI",
  "checks": [
    "metadata",
    "privacy"
  ],
  "ready": true
}

Invalid input{"ready":}

Rejected because the property has no value. MCXAI does not assume true, false, null or an empty string.

Four common inputs that are not JSON

They may be valid in JavaScript or JSON-like configuration formats, but a strict JSON parser must reject them.

Trailing commas{"ready": true,}

Remove the comma after the final member.

Single-quoted strings{'ready': true}

JSON strings and object keys require double quotes.

Comments{"ready": true /* note */}

Standard JSON has no comment syntax.

Undefined values{"ready": undefined}

Use null only when an explicit empty value is intended.

Formatting does not make data safe

A valid JSON document can still contain credentials, personal data, unsafe HTML or values that another system interprets dangerously.

Input is limited to 1 MB
Comments and trailing commas are not valid JSON
Large nested values remain text-only
Remove secrets before pasting data into any browser-based utility.

Preparing the page

Public context is loading before any interactive tool code.

Validate · format · inspect

Format JSON and find syntax errors locally

Validate and pretty-print JSON in the browser with precise parse errors and no upload.

Parser testedReviewed 2026-07-18

JSON input72 characters

Result

Your checked result will appear here.

Standards-basedValidation uses the browser's built-in JSON parser.LocalThe JSON value never leaves this browser tab.Reviewed2026-07-18

Reject the broken branch before formatting the rest

Pretty printing is the final step. The parser first checks that the entire value follows JSON syntax, then serializes the parsed value with two-space indentation.

What happens after you press Format JSON

No repair is applied behind your back. Invalid syntax returns an error instead of guessing what the missing value should be.

1Check the limit
Inputs over 1 MB are rejected before parsing to keep the browser responsive.
2Parse the whole value
Objects, arrays, strings, numbers, booleans and null must all follow JSON grammar.
3Stop on syntax errors
The parser reports the failure instead of producing a partially trusted result.
4Serialize consistently
A valid value is returned with stable two-space indentation for inspection or copying.

One valid fixture, one deliberate failure

Both cases are regression-tested. The displayed output is produced by the same functions used in the workbench.

Compact input

{"project":"MCXAI","checks":["metadata","privacy"],"ready":true}

Formatted output

{
  "project": "MCXAI",
  "checks": [
    "metadata",
    "privacy"
  ],
  "ready": true
}

Invalid input{"ready":}

Rejected because the property has no value. MCXAI does not assume true, false, null or an empty string.

Four common inputs that are not JSON

They may be valid in JavaScript or JSON-like configuration formats, but a strict JSON parser must reject them.

Trailing commas{"ready": true,}

Remove the comma after the final member.

Single-quoted strings{'ready': true}

JSON strings and object keys require double quotes.

Comments{"ready": true /* note */}

Standard JSON has no comment syntax.

Undefined values{"ready": undefined}

Use null only when an explicit empty value is intended.

Formatting does not make data safe

A valid JSON document can still contain credentials, personal data, unsafe HTML or values that another system interprets dangerously.

Input is limited to 1 MB
Comments and trailing commas are not valid JSON
Large nested values remain text-only
Remove secrets before pasting data into any browser-based utility.

Start with your source

Reject the broken branch before formatting the rest

What happens after you press Format JSON

One valid fixture, one deliberate failure

Four common inputs that are not JSON

Formatting does not make data safe

Validate first, transform second

Start with your source

Reject the broken branch before formatting the rest

What happens after you press Format JSON

One valid fixture, one deliberate failure

Four common inputs that are not JSON

Formatting does not make data safe

Validate first, transform second