Jess Information

Jess Home
Jess 7 Features
Download Now!
Online Demo

Mailing List
Jess Wiki

More information Related Web Sites
User Contributions
JSR94 Info
About This Site

JESS ®, the Rule Engine for the JavaTM Platform


Jess 7.1p2 is released!

Jess is a rule engine and scripting environment written entirely in Sun'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 can be licensed for commercial use, and is available at no cost for academic use. Contact Craig Smith at for prices and commercial licensing terms, or for a research based academic license. A trial download is also available.

Technical questions or comments? Contact Ernest Friedman-Hill at

Last modified: Tue Nov 11 10:24:07 EST 2008

Jess and the Jess design are registered trademarks of Sandia National Laboratories. Java and all Java-based marks are trademarks or registered trademarks of Sun Microsystems, Inc. in the U. S. and other countries.