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JESS ®, the Rule Engine for the JavaTM Platform


The first public alpha of Jess 8.0 is now available to licensed users on the Downloads page. Jess 8.0 includes support for the Android platform.

Jess is a rule engine and scripting environment written entirely in Oracle's® Java™ language by Ernest Friedman-Hill at Sandia National Laboratories in Livermore, CA. Using Jess, you can build Java software that has the capacity to "reason" using knowledge you supply in the form of declarative rules. Jess is small, light, and one of the fastest rule engines available. Its powerful scripting language gives you access to all of Java's APIs. Jess includes a full-featured development environment based on the award-winning Eclipse platform.

Jess uses an enhanced version of the Rete algorithm to process rules. Rete is a very efficient mechanism for solving the difficult many-to-many matching problem (see for example "Rete: A Fast Algorithm for the Many Pattern/ Many Object Pattern Match Problem", Charles L. Forgy, Artificial Intelligence 19 (1982), 17-37.) Jess has many unique features including backwards chaining and working memory queries, and of course Jess can directly manipulate and reason about Java objects. Jess is also a powerful Java scripting environment, from which you can create Java objects, call Java methods, and implement Java interfaces without compiling any Java code.

Jess is available at no cost for academic use and can be licensed for commercial use. Contact Sandia National Laboratories at for a research based academic license, or for for prices and commercial licensing terms. A trial download is also available.

Technical questions or comments? Contact Ernest Friedman-Hill at

Last modified: Mon Nov 25 10:14:20 PST 2013

Jess and the Jess design are registered trademarks of Sandia National Laboratories. Oracle and Java are registered trademarks of Oracle and/or its affiliates. Other names may be trademarks of their respective owners.