Is there an offline JSON formatter download for Windows or Mac?

Install Tool Kumar from Chrome or Edge, or use Add to Dock in Safari on supported macOS versions. It is a web app, not a separate .exe or .dmg download.

Can desktop Firefox use it offline?

Yes, when service workers and site storage are enabled and the first visit has finished caching. If your Firefox version has no install option, keep the site in a tab or bookmark it.

Can I use the formatter in airplane mode?

Yes, after an online visit has cached the app. Reload the homepage and test with a sample before relying on it without a connection.

How does the offline app update?

An online homepage load refreshes the cached shell and its assets. When a changed asset set is ready, an open tab offers a Reload message. Close and reopen or reload to use the new version.

Where is my JSON stored?

User-edited JSON is saved in this browser's localStorage when it fits the 2,500,000-character limit. Compare text, file name, settings and theme can also be stored. The service worker cache stores application resources.

Offline JSON formatter for Windows, Mac and mobile

How to use this tool

Open Tool Kumar while connected and wait a few seconds after the page finishes loading. Allow the browser to store site data.
Open DevTools, choose Network, change the throttling menu to Offline and reload the homepage. On a phone, enable airplane mode and reload.
Paste the sample and confirm formatted output appears. Test conversion too if you need it, then return Network to its usual setting.

Worked example

The same local formatter produces this output online or after its application assets have been cached for offline use.

Input

{"user-id":42,"display name":"Ada","class":true,"profile":{"city":"London","created_at":"2026-10-14T09:00:00Z"},"items":[{"sku":"A1","price":12,"note":null},{"sku":"B2","price":12.5,"note":"gift"}],"metadata":null}

Output

{
  "user-id": 42,
  "display name": "Ada",
  "class": true,
  "profile": {
    "city": "London",
    "created_at": "2026-10-14T09:00:00Z"
  },
  "items": [
    {
      "sku": "A1",
      "price": 12,
      "note": null
    },
    {
      "sku": "B2",
      "price": 12.5,
      "note": "gift"
    }
  ],
  "metadata": null
}

Install on Windows, macOS, Linux or ChromeOS

In Chrome, open the browser menu and choose Cast, save, and share, then Install page as app. An install icon may also appear in the address bar. In Edge, choose Settings and more, Apps, then Install this site as an app. Menu labels vary by browser version.

On macOS Sonoma or newer, Safari offers File, Add to Dock. Open the app once while online and run the offline check before disconnecting. Installation does not replace the caching step.

Desktop Firefox may not offer to install the site as an app. You can still use the cached site offline in a Firefox tab when service workers are enabled.

Install on iPhone, iPad or Android

On iOS or iPadOS, open the site in Safari, tap Share and choose Add to Home Screen. Enable Open as Web App if your version offers that switch, then tap Add.

On Android, open the site in Chrome, tap the menu and choose Install app or Add to Home screen. Open it online first and wait for caching before enabling airplane mode.

Check caching and clear local data

In Chromium DevTools, Application, Service Workers shows the registered worker. Cache Storage shows the json-viewer cache, and Local Storage shows the jf: keys. The cache holds app assets; localStorage can hold your edited document.

To remove both, close other Tool Kumar tabs, then use Application, Storage, Clear site data, including local storage, cache storage and service workers. Other browsers provide equivalent site-data controls in their settings. You will need an online visit before offline use works again.

Use sensitive JSON offline

Test offline mode with a harmless sample first. Once the app works with networking disabled, paste sensitive data. Browser extensions with page access can still read it. Clear the site data when you finish on a shared device.

Options and edge cases

Installation is optional. The service worker makes the cached homepage work in a normal browser tab too.
The app caches its homepage, JavaScript, styles, fonts, icons and conversion modules. Visited full pages can be cached; an uncached page falls back to the homepage.
Remote URL loading needs a connection. Analytics and cross-origin requests are not cached. Offline internal navigation can also fall back because Next.js route data is not cached.
Offline use depends on the browser retaining site storage. Clearing site data, private browsing policies or storage eviction can remove the app cache.

Private by default

Your document stays in this browser. Tool Kumar parses, converts and creates downloads on your device, with no account or upload step.

Offline JSON formatter questions

Is there an offline JSON formatter download for Windows or Mac?: Install Tool Kumar from Chrome or Edge, or use Add to Dock in Safari on supported macOS versions. It is a web app, not a separate .exe or .dmg download.
Can desktop Firefox use it offline?: Yes, when service workers and site storage are enabled and the first visit has finished caching. If your Firefox version has no install option, keep the site in a tab or bookmark it.
Can I use the formatter in airplane mode?: Yes, after an online visit has cached the app. Reload the homepage and test with a sample before relying on it without a connection.
How does the offline app update?: An online homepage load refreshes the cached shell and its assets. When a changed asset set is ready, an open tab offers a Reload message. Close and reopen or reload to use the new version.
Where is my JSON stored?: User-edited JSON is saved in this browser's localStorage when it fits the 2,500,000-character limit. Compare text, file name, settings and theme can also be stored. The service worker cache stores application resources.