JSON Validator

Valid or not.

Find out instantly.

Input
Output
No upload
Works offline
No idea what's in your data

Need to validate thousands of JSON files? The offline bundle handles batches with no size limit. $99 once.

Get Bundle →
// How it works

Three steps. Zero uploads.

01
Paste
Paste your JSON or drop a .json file. It stays on your device.
02
Validate
fwip validates instantly and highlights any syntax errors with line numbers.
03
Fix
See exactly what's wrong. Nothing was ever sent anywhere.
// Why this is different

Your data never leaves your machine.

Most online JSON validators send your data to a server for processing. Your JSON passes through systems you don't control.

fwip works differently. The validator runs entirely in your browser. Your data is read from your device, processed on your CPU, and the result is saved back to your device. No server is involved. We literally cannot see your file.

No server processing

Everything runs on your device using WebAssembly. Your file never touches a network.

No account required

Drop a file. Get a result. No sign-up, no email, no password.

No subscription

Free in the browser. $99 once for the offline bundle. That's it. Forever.

Works offline

The desktop version works with no internet connection at all.

// Questions

Frequently asked.

How do I validate JSON online?▾
Paste your JSON into fwip. It validates instantly in your browser and highlights any syntax errors with line numbers.
Is it safe to validate JSON with API keys?▾
Yes. fwip validates entirely in your browser. Your JSON never hits a server — safe for production data and credentials.
What JSON errors does it catch?▾
Missing brackets, trailing commas, unquoted keys, invalid escape sequences, and all other JSON syntax errors.
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Offline. No browser. No internet. No excuses.
$15
This tool
  • JSON Validator · offline
  • Batch processing
  • No file size limit
  • 3 devices · one payment
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Complete suite
  • All 200+ tools · offline
  • No file size limit
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One-time payment · 3 devices · Updates included · Mac + Windows + Linux