Why it's a strong pick

JSON Formatter does one job: it makes a page of raw JSON readable. It is open source under the BSD-3-Clause license, and its code is public on GitHub. It uses Manifest V3, Chrome's current extension format. Its manifest was last updated in January 2026.

What it does

Open a URL that returns JSON, and the extension replaces the wall of text with a tree. You fold and unfold branches, see colors by type and click links. You can switch back to the raw text at any time.

Key features

Collapsible tree. Fold branches, with indent guides to keep your place.
Syntax highlighting. Strings, numbers and other types have their own colors.
Dark mode. Easier on the eyes at night.
Clickable URLs. Links inside the JSON are links you can click.
Raw and parsed toggle. Flip between the formatted view and the original text.
Console access. The parsed JSON is available as a global called json in the console.
Long JSON. The README says it stays fast on long files.

Who it's for

JSON Formatter is for developers, and for anyone who reads API responses in the browser. If you open JSON URLs only once in a while, it still saves you from squinting at one long line.

What permissions does JSON Formatter ask for?

Its manifest asks for storage, unlimitedStorage and webRequest. It lists access to all sites, runs content scripts on all pages, and one of them runs in the page's own context. It needs Chrome 88 or newer. We could not read the developer's privacy policy when we checked; read it before installing.

Does it change big numbers?

It can. The extension uses the browser's own JSON.parse, so numbers larger than 9007199254740991 are rounded, as the README notes. If you work with very large IDs, check them in the raw view rather than the tree, and compare with the source.

Can I use the data in the console?

Yes. The parsed JSON is exposed as a global called json, so you can open DevTools and type json to explore it. This is handy for a quick look at one field, or for trying out a filter, without writing any code first.

FAQ

Can I see the original text? Yes. Use the raw and parsed toggle.

Does it have a dark mode? Yes, the README lists dark mode.

Is it open source? Yes, under the BSD-3-Clause license.

Good to know

The tree shows the parsed object, not the exact text sent by the server. When the exact text matters, such as for a very large number, switch to the raw view. Also note it asks for access to all sites, because it must see any page that returns JSON.

Other developer tools to compare

JSON Formatter is one of 13 picks in our developer tools guide:

Lighthouse: audit a page.
Redux DevTools: debug Redux state.
Apollo Client Devtools: inspect Apollo Client apps.
Preact Developer Tools: inspect Preact components.
React Developer Tools: inspect React components.
Vue.js devtools: inspect Vue 3 apps.
Requestly: Open-source HTTP interceptor: redirect URLs, modify headers and mock requests while you test.
Solid DevTools: debug SolidJS reactivity.
Ember Inspector: inspect Ember.js apps.
MobX Developer Tools: debug MobX apps.
Refined GitHub: Simplifies GitHub and adds 100+ small improvements for repos and pull requests. Works on GitHub.com only. Open source.
Header Editor: Rewrites request and response headers, redirects and blocks requests with rules you set. The Chrome build is the Lite version. Open source.