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Kiwix JS 4 0 Anniversary

Kiwix JS

Kiwix is your gateway for offline access to vast web resources like Wikipedia, Stackexchange, Project Gutenberg, TED Talks, and much more. These resources are packaged as highly compressed ZIM archives available for free from Kiwix. Learn more about the open-source Kiwix project on our main website.

Kiwix JS is our official HTML5/JavaScript version, primarily designed for browser extensions. Grab our free extension from the Mozilla, Chrome, and Edge extension stores. Check out the Store links for more details. We also offer an offline-first Progressive Web App (PWA) version at For a fully featured PWA based on Kiwix JS, visit

To get started with Kiwix JS, download a free content archive (Usage), select it on your device, and start exploring articles. You can access the entire content of Wikipedia in your language, including images and audiovisual content, offline. Ideal for users with expensive, intermittent, slow, unreliable, or censored internet access. You can even load ZIM archives shared on a USB stick or external hard drive. No internet? No problem!

Kiwix supports all content in the OpenZIM format, including full support for Zimit content (based on the Web Archive format), both Zimit Classic and Zimit v2.0. Note: Some content requires your browser to support Service Workers.

Build Status: Continuous Integration Build Status: Release CodeFactor Licence: GPL v3

Kiwix for Firefox Kiwix for Chrome Kiwix for Edge


Install "Kiwix JS" from your browser's add-on store. This is the best way to get the extension, because it will be kept up to date automatically. If you would rather not use a store, you can get a file-based version of the extension from (and follow instructions below), but you will have to update this manually.

Alternatively, you can bookmark or install the PWA version from (it will auto-update), or try our dedicated PWA version at To install the PWA (in Chromium browsers), go to Settings -> Apps -> Install this site as an app.

As mentioned above, the app requires at least one ZIM archive of offline content. You can download one from the in-app library, or else in any browser go to (this has a nice, graphical interface and a preview of each ZIM archive) or from (a more basic list of archives). You have to download these separately, store them in your filesystem, and manually select them after starting the application (or you can drag-and-drop one into the app).

Zimit-based archives (available from the "zimit" directory on, or made yourself with, are fully compatible with this reader. For the best experience, you will need a modern browser and to allow the app to run in ServiceWorker mode as an offline-first PWA (see below for an explanation of what this means). If the app is running in any other mode, then only static content will be viewable (if at all). Our sister app has some further support for Zimit archives in older browsers.


Be sure to get your ZIM archives only from a secure source, such as the official Kiwix library. This is because ZIM archives can run dynamic code in your browser. While we do our best to sandbox the ZIM's content, a detemined malicious ZIM could remove the sandbox and redirect the iframe to, say, a phishing Web site. For this reason we now show a Security Warning when you open a ZIM with dynamic content in ServiceWorker mode for the first time. If you do not trust the source of the ZIM, and wish to browser static content safely, then open the ZIM first in Safe Mode before deciding whether to switch to ServiceWorker Mode.


Since the app is written in HTML/JavaScript, it should work in most recent browser engines and many older ones too, depending on the Content Injection mode supported by the specific browser engine. Archives containing dynamic content (most non-Wikimedia archives) work better in ServiceWorker mode (see below), but unfortunately this is not available in many older browsers. If you wish to read such archives, we would suggest that you upgrade to a browser that supports Service Workers (Chrome 58+, Firefox 61+ [not ESR versions], Edge 17+, Safari 11.3+).

Officially supported platforms

Deprecated platforms

These platforms/browsers are deprecated. We still partially test against them, and we'll try to keep compatibility as long as it's not too complicated:

  • Firefox OS >=1.2: needs to be installed manually on the device with WebIDE
  • Microsoft Edge Legacy >=17: no extension available, but bookmark or
  • Microsoft Edge Legacy 15-16: needs to run a bundled version of the source code in Safe mode only
  • Microsoft Internet Explorer 11: needs to run a bundled version of the source code in Safe mode only

You can build a bundled version by running npm install and npm run build in the root directory of this repo. Alternatively, a bundled version is served as a web app for testing from (also available on the gh-pages branch of this repo, under /dist).

Installing signed or unsigned extension files in Chromium

If you need to install Chromium (Chrome or Edge) extension from a file instead of from a Store, e.g. if your browser doesn't support Manifest V3, then you will need to download a signed or unsigned CRX or ZIP file from a relevant directory in, or else a nightly version from Files with mv2 in their filename are in the legacy Manifest V2 format.

To install your CRX or ZIP, open the extension management page in your browser, e.g. chrome://extensions/ or edge://extensions/, and turn on Developer mode. Now, you should be able to drag and drop the ZIP file into this page. Verify the extension is showing in the management page.

Files that we deliver with a .crx file extension are files that have been validated by the Edge or Chrome Stores, and you should be able to install these as "first-class" apps. ZIP files provided in, or the ones labelled signed in nightly, are actually signed CRX files that have been renamed with a .zip extension to facilitate downloading and installing them in Chromium browsers. Although signed, you cannot install them as CRX files, because they have not been validated by the Chrome or Edge Stores. For this reason, the browser will periodically ask you if you want to turn off developer-mode extensions. Just choose "ask again in two weeks".

If drag-and-drop is difficult, you can instead unzip the extension ZIP into a folder, and note the location. Then select "Load unpacked" and choose the folder that contains the unzipped extension. To unzip the MV2 files with a utility like 7Zip, you will need to change the extension name to .crx. On Linux, unzip can read them without changing the filename.

Some technical details

Technically, after reading an article from a ZIM file, it is necessary to "inject" the dependencies (images, css, etc). For compatibility reasons, there are two main ways of doing this:

  • "ServiceWorker" mode (the default) uses a Service Worker to catch any HTTP request the page may send and reply with content read from the ZIM file. It is a generic and clean way of serving content to the browser. It works in any recent browser, but not in older ones. Service Workers are currently disabled by Mozilla in Firefox extensions, and in Chromium extensions active content is severly restricted for security reasons. In both cases we offer a functional workaround (an offline-first PWA version) as a substitute within the extension;
  • "ServiceWorkerLocal" mode is a restricted ServiceWorker mode that is available only in Chromium extensions running fully locally. Chromium extensions running locally block (by design) a lot of dynamic content such as inline JavaScript and eval, which means this mode won't work with some modern dynamic content, and in particular, it won't work with Zimit-based archives (if you open one of these in this mode, you will be thrown back to Safe mode in order to view static content). However, this mode is useful if you cannot access the offline-first PWA, and should work with most official Kiwix ZIM archives;
  • "Safe" mode prevents running attached scripts in the iframe, and so is useful for checking the contents of a ZIM before deciding it is safe to run. This mode also works in browsers that do not support Service Workers. It parses the DOM to find the HTML tags of the dependencies and modifies them to point to content we extract from the ZIM. This mode is compatible with any browser, but becuase it cannot run JavaScript inside the ZIM file, does not work well (if at all) with ZIMs that depend on dynamic content. If you open a dynamic (including Zimit) archive in this mode (or if you are thrown into the mode due to another incompatibility), then we will do our best to display static content, but much functionality is likely to be broken. However, Mediawiki-based content (e.g. Wikipedia) works fine in this mode.

You can switch between these content injection modes in Configuration, but if your browser supports ServiceWorker mode as an offline-first PWA, you are strongly advised to remain in this mode (unless you wish to check the safety of a ZIM before running it -- the UI will ask you if you wish to do this when you first open a new ZIM).

File access and other limitations

You can only re-open an archive automatically if your browser supports the File System Access API and allows you to grant permanent access permission. In practice, this currently means Chromium browsers (Chrome, Edge, etc.) with a version number of 122 or higher. If that is the case, you will see a popup asking you whether you wish to grant access "on every visit" (this will appear only after the second or third time that you have picked an archive or folder). If you grant this permanent permission, then the browser will (optionally) re-open the last-visited archive when you open the app.

In other cases, your browser may fall back to using the webkitdirectory property of the File API, which allows you to re-open a folder or directory of ZIMs with a quick permission prompt. Another alternative is to drag-and-drop a ZIM file into the app.

There are versions of this app that have experimental support for the Origin Private File System, or that use frameworks like Electron, which do have the capability of remembering the chosen archive between app launches.

The app has fast title search, and slower full-text search for ZIM archives that have a full-text index, thanks to the openzim/javascript-libzim project. Currently, full-text searching only works in browsers that support Atomic Operations, which means recent desktop versions of Chromium and Firefox. There is also support in Safari on iOS 15+.


This application is released under the GPL v3 licence. See or the included LICENSE-GPLv3.txt file The source code can be found at


Kiwix JS is an open-source project. We encourage individuals with experience of HTML and JavaScript development to contribute to the documentation and code in this repository.

To report a bug, read our REPORT_BUG guide.

For code contributions, read our CONTRIBUTING guide.

To get to know the Kiwix project better, please familiarize yourself with the content on There is also a Kiwix Slack group which you can join.

We also have a CODE_OF_CONDUCT: everybody is expected to follow it.

Public releases and nightly builds

The browser extensions are distributed through the stores of each vendor (see links above). But the packages are also saved in if necessary.

Some nightly builds are generated, and should only be used for testing purpose:

There is a test implementation of the latest code at (unbundled: needs a modern browser that suppors native ES6 modules), and a bundled version for any HTML5 browser (>=IE11) at, but these implementations are used for development, and may be buggy, experimental or unstable. A stable PWA version for use in the browser extensions is available from

Previous versions

The first versions of this application were originally part of the Evopedia project: (discontinued). There was an "articles nearby" feature, that was able to find articles around your location. It has been deleted from the source code with everything related to Evopedia (but still in git history in versions<=2.0.0).

These first versions were targeting Firefox OS (discontinued too: we're not lucky ;-) ).

See for details of previous versions.