The CheerpJ browser extension for applets runs Java applets in modern browsers, with no Java plug-in and no Java installed on the computer. It runs each applet in place, on the page where it has always been. It is listed as CheerpJ Applet Runner in the Chrome Web Store and Edge Add-ons.

The extension is built on CheerpJ, a Java runtime built from OpenJDK and compiled to WebAssembly. The CheerpJ browser extensions have more than 170,000 users together.

What it runs

• Java: Java 8 applets, with their Swing and AWT interfaces.
• Browsers: Chrome, Edge and other Chromium browsers, on desktop.
• Files: upload files from a button in the applet’s title bar; files the applet saves arrive as browser downloads. See upload and download files.
• Also: networking, audio, printing and the clipboard, through the browser.

The applet, its data and its traffic stay between your browser and the applet’s server, and don’t pass through us.

For an applet on a page you control, you can also add CheerpJ to the page, so visitors need no extension. To build with CheerpJ, see the CheerpJ documentation. For a Java Web Start (.jnlp) application, use the extension for Java Web Start.

Getting started

1. Install the extension in Chrome or Edge, and pin it to the toolbar.
2. Open a page with an applet, click the extension’s icon and turn on Enable for this domain.
3. The applet starts. The extension stays on for that site, so its applets start by themselves next time.

See using the extension for the first time for a walkthrough.

For organisations

With an Enterprise licence, desktop administrators deploy the extension to managed Chrome and Edge through Group Policy or Intune, and set the licence by policy, where it activates offline. A self-hosted version serves networks that can’t reach the stores, including air-gapped ones. See configure the extension for enterprises and private hosting.

Licensing

Free for personal use and technical evaluation. Business use needs a Desktop licence, bought online for up to 20 desktops. Larger deployments use Enterprise licences, which need no licence server. See licensing.

Privacy

If you activate a licence, the extension checks it with our licence server. It collects no usage statistics. The details are in the privacy policy.

Help and bug reports

Use Report a Bug in the extension’s popup, or open an issue on GitHub. Issues are public: for an applet on an internal or private site, write to appletrunner@leaningtech.com instead. To collect logs for a report, see how to debug the extension.

Questions are welcome on Discord.