Pass exists
TLE geometry estimates the pass window, max elevation and local timing.
ISS and Starlink visible tonight
A satellite pass existing does not mean it is worth seeing.
Heavens-Above, NASA and satellite trackers show when objects pass overhead. DarkestHour adds the sky-condition filter: cloud, moon, darkness and local visibility before you leave the couch.
Cloud gap
A perfect pass is a miss if low cloud covers the sky during the window.
Dark enough
Moon altitude and illumination decide whether faint trails or contrast will survive.
Photo-worthy
Pro should score whether the pass is worth setting up a tripod or changing plans.