Large Transport
Air Traffic Control Fully Certified
Air Traffic Control Time Certified In Pos 1 (yrs) 15
Distraction
ATC Issue All Types; Conflict Ground Conflict; Less Severe; Ground Incursion Runway
Air Traffic Control Separated Traffic; Air Traffic Control Provided Assistance
Aircraft; Human Factors
I issued Line Up And Wait to Aircraft X Runway 1 Left.  I do not recall if I said traffic landing both Runway's 28 Left and Right; which I do as often as possible to keep myself abreast of the traffic as well as pilot expectation.  When the Runway 28 Right arrival rolled through; I cleared Aircraft X for take-off.  The Local Assist calmly said you didn't clear them did you; as they pointed to Aircraft Y over the approach lights.  I cancelled Aircraft X's take off clearance and received an immediate acknowledgement.  Since I received the immediate acknowledgement and Aircraft Y was still outside the threshold; I allowed Aircraft Y to land.  The Front Line Manager said good job team.I have an idea why Aircraft Y disappeared from my scan.  I had just been discussing with my Local Assist the similar looking data blocks for the next two arrivals Aircraft Z & Aircraft A.  I use every tool I can to not only maintain my situational awareness; but also those of my tower team and the pilots.  I strive to be as accurate and complete as possible with every transmission make so that there is maximum benefit to the information exchange.
A SFO Local Tower Controller reported clearing an aircraft for takeoff. Local Assist questioned the Controller and pointed to an arrival aircraft. Local then cancelled the takeoff clearance and let the aircraft land. The reporter stated distraction related to similar looking call signs of aircraft on final contributed to the event.