A Programmable plug system for accessing and isolating formations during hydraulic fracturing, consisting of a Programmable Plug and plurality of Sliding Sleeve Valves installed in the casing string of a wellbore, wherein Programmable Plug travels, downwards or upwards through the casing and Sliding Sleeve Valves, wherein during its travel the Programmable Plug detects and counts each sleeve using on-board sensors, electronics and software and wherein the Programmable Plug utilizes detected information to locate, activate and engage itself into the Sliding Sleeve Valves, one at a time, from the top or from the bottom, without locking in, according to programmed sequence (to open, close or bypass) stored in the on-board memory. When engaged to the Sliding Sleeve Valve from the top, the Programmable Plug opens the Sliding Sleeve Valve by applying the pump pressure from the surface, thus providing access to the zone adjacent to the Sliding Sleeve Valve while sealing and isolating the zones below the Sliding Sleeve Valve. Applying pressure in opposite direction, or pulling on by the wire line or slick line winch connected to the Programmable Plug causes the Programmable Plug to disengage itself and travel up the casing string towards next Sliding Sleeve Valve where setting, actuation, and opening is repeated for that Sliding Sleeve Valve. To close open Sliding Sleeve Valve, Programmable plug engages Sliding Sleeve from the bottom side and pushed up by well pressure from the bottom or pulled upwards by the slick line or wire line winch, thus closes the Sliding Sleeve Valve.