Method. Sun, Moon & planet positions use standard low-precision orbital elements (Meeus/Schlyter), accurate to a few arcminutes — plenty for "is it up and roughly where," not precision goto pointing. Planet magnitudes are computed per-apparition from real photometric fits (Mallama & Hilton 2018), not fixed values — Saturn's is globe-only (no ring-tilt boost, which can add several tenths of a magnitude when the rings are wide open), and Uranus/Neptune omit a small pole-orientation term worth a few hundredths. Deep-sky coordinates are catalog J2000 values. Sky darkness for 98374 is an estimate (suburban Seattle–Tacoma metro, roughly Bortle 6–7) — check the live map above for your exact yard.
Visibility. The "should be visible" call on deep-sky targets models real local sky brightness right now — your Bortle estimate plus the moon's actual position and phase, via the Krisciunas & Schaefer (1991) scattering model — then checks it against each object's surface brightness (galaxies/nebulae) or a sky-brightness-adjusted telescopic limit (star clusters and doubles, which shrug off light pollution far better than diffuse light). Most galaxies/nebulae use whole-object average surface brightness, which understates anything with a bright compact core or rim — M31 and M27 use their real, brighter core/rim values instead, so a plain galaxy tagged "washed out" may still show a faint nucleus. It also assumes a typical clear-night extinction coefficient, not a measurement of your actual air that night — treat close calls as "worth a look," not gospel.