It consists of over 5000 precisely defined rules that return closed-form antiderivative for a wide class of integrands. Also available is a test suite comprised of almost 50,000 integrands and their optimal antiderivatives.
An almost total rewrite of the trig integration package has greatly increased the class of expressions Rubi is able to integrate. For example, Rubi 4.5 can integrate all integrable expressions of the form
where <trig> is any one of the twelve trig or hyperbolic functions. Note that the coefficients and exponents can have any numeric or symbolic value, including zero. Of course, Rubi automatically transforms a wide variety of other trig expressions into the above form so they can be integrated. Previous versions of Rubi could only guaranteeably integrate all expressions of the form