G.191 Annex A describes the ITU-T Software Tools Library release 2000 (STL2000). The STL2000 contains improvements and error corrections of the STL96 (the version of the ITU-T STL approved in 1996). In particular, a G.727 module, new filter types, and a Basic Operator module have been added, as well as support for more modern compilers. This Recommendation includes an electronic attachment containing STL2000 Software Tool Library and manual.