The input and output formats, and the structure of Rule Input Network Generator (RING), a computational tool for generation and analysis of complex reaction networks, are described with reference to the underlying algorithms from Cheminformatics and graph theory. RING consists of three modules: (a) a compiler that translates inputs written as a program in an English-like reaction language into internal representations and instructions, (b) a network generator that constructs an exhaustive reaction network from reaction rules and initial reactants specified, and (c) a post-processing module that can extract pathways, mechanisms, or lumps from the network based on user-specified instructions. RING can be used, in a rule-based manner, for constructing a large and complex reaction network from a set of elementary/overall reaction rules, and for elucidating transformations occurring in these networks through identifying pathways and mechanisms to specified products. RING is available open under GNU Lesser GPL. (C) 2012 Elsevier Ltd. All rights reserved.