What is OpenWebStart?

OpenWebStart is an open source reimplementation of the Java Web Start technology. It provides the most commonly used features of Java Web Start and the JNLP standard, so that your customers can continue using applications based on Java Web Start and JNLP without any change. OpenWebStart is based on Iced-Tea-Web and the JNLP-specification defined in JSR-56. OpenWebStart is released under the GPL with Classpath Exception. For more information, read the full license here.

The main focus of OpenWebStart is the execution of JNLP-based applications. Additionally, the tool contains four modules that simplify your Web Start workflows and let you configure OpenWebStart to suit your needs:

App Manager

manages the versions of any JNLP-based application that is executed by OpenWebStart.

JVM Manager

manages Java versions and Java updates on the client.

Control Panel

provides a graphical user interface to configure OpenWebStart.


downloads and installs new versions of OpenWebStart.

Which JNLP features will be supported?

Nothing will change from the point of view of your users. OpenWebStart will provide exactly the same JNLP-based workflow as Java Web Start:
  1. A user either clicks a link on a webpage, or an automated provisioning process downloads a JNLP file to the client. The JNLP file describes the application.
  2. OpenWebStart registers itself as default for the JNLP file extension and the MIME-type application/x-java-jnlp-file. From now on, OpenWebStart launches when users double-click any JNLP file.
  3. OpenWebStart parses the JNLP file, downloads all required resources (JARs, native libraries and images), and stores them in a cache.
  4. When all resources are downloaded, the application starts.

How do I install and manage OpenWebStart?

OpenWebStart comes in two different versions:

  • An interactive installer with auto-update functionality
  • An unattended installer for automated roll-outs

If you use Web Start for several small customers or on your own, we recommend using the interactive installer. Our native installer will set up everything on your Windows, Mac, or Linux system so that OpenWebStart is immediately ready to use. OpenWebStart checks for updates automatically, and the Updater component keeps the tool current without the need for any user interaction.

If you or your customers are companies with IT departments of their own, we recommend an unattended installation to roll out OpenWebStart on multiple client machines. In this scenario, the auto-update functionality is inactive; your IT department is free to plan and handle rollouts of new versions based on your internal workflows.


OpenWebStart follows a half-yearly release cycle. The releases are targeted around May and November each year. These regular releases usually contain bugfixes as reported by sponsors and the community as well as recurring maintenance issues to guarantee stability and topicality.

Hot-fix releases may be published at any time (independent of the regular release cycle). The same applies for customer-specific releases. For customer-specific releases, a support contract with Karakun is needed.

New features are currently only developed when a sponsor can be found. Contact us for an individual offer.