Workbench is free to use, but is not an official salesforce.com product. Workbench has not been officially tested or documented. salesforce.com support is not available for Workbench. Support requests for Workbench should be directed to Stackoverflow at https://salesforce.stackexchange.com/questions/tagged/workbench. Source code for Workbench can be found at https://github.com/forceworkbench/force