# Saving and Using Input Files

The File menu save and save as selections can be used to save input files with the RuleBuilder .bng extension. An advanced user many additionally save with the BioNetGen Engine .bngl extension that can be used in running the BioNetGen Engine code manually outside the RuleBuilder interface.

Input files are easily read back into RuleBuilder via the File menu open selection. The .bng format allows for a model to be read back into the RuleBuilder display and will automatically repopulate the Molecule Template, Species and Reaction Rules windows. The remaining palette windows are also repopulated and may be reselected for display via the View menu.