Geometry Constructions Language (gcl) is a language for explicit descriptions of constructions in Euclidean plane and of their properties. Other mathematical objects can also be described in the language. The language gcl is intuitive and simple, yet it supports arrays, flow control structures, user-defined procedures, etc. The processors for the gcl language-applications gclc and Wingclc-enable visualization of described objects and producing of mathematical illustrations, provide different semantical information and support for automated proving of properties of the constructed objects. These features make the tools gclc and Wingclc powerful mechanized geometry systems and they have thousands of users worldwide.