The MIME type application/x-java-jnlp-file is used to denote the presence of JavaWS files, also known as Java Web Start. This MIME type is categorized under "application".

The Java Web Start files carry the extension JNLP. Java Web Start, also known as JavaWS or javaws, is a framework that allows users to trigger Java applications directly on the Internet from within their browsers. Java applications are application softwares written for the Java platform or the Java Runtime Environment (JRE). Although this may sound similar to Java applets, the Web Start applications do not actually run inside the browser. Also, the sandbox in which Web Start applications run does not have as many restrictions. However, this aspect can be changed when it is being configured.

Web Start has the advantage of compatibility when compared to applets. It can work through the compatibility issues that plague the Java plugins for the browsers and the different java Virtual machine (JVM) versions. However, in doing so there is a trade off required in communications. Web Start programs cannot communicate with browsers as well as applets can.

There is one feature through which a user can invoke a Java applet as a Java Web Start application to assist in migration.