The Lasso Java Application Programming Interface (LJAPI) allows Java programmers to extend Lasso's functionality on the server side.

LJAPI allows one to create Lasso command and substitution tags as well as receive values and parameters passed to them. These tags function exactly as the standard set of tags currently shipping with Lasso.

LJAPI also allows one to write new data source modules which can be used in conjunction with any of the core set of Lasso database-related tags.