The hard filters like "# of players" and "available time" limit the selections to games that fit those parameters. Difficulty is a soft filter, which means that it will favor games close to the selected difficulty level, but not eliminate games of higher or lower difficulties. This is because of a "difficulty score" modifier on the "match score". If the game’s number matches your choice exactly, the formula gives the game a one-point bonus; if it is only one step easier or harder, it still gets a smaller half-point boost. When it is two steps off, the score is nudged down by a quarter-point, and if it is three steps off, the penalty grows to half a point. If you leave the selector on “Any,” the difficulty difference is ignored and no bonus or penalty is applied.

The "match score" determines how well of a match the game is, and how they are sorted in the suggestions section. Along with the difficulty score modifier, it is effect by the "player match" modifier and the "rating" modifier. The rating modifier is simply the BGG rating and is applied to add slight favor to better ranked games. The player match formula first grabs the group size you selected and looks up its hard minimum and maximum player counts along with the “ideal” ranges contributed by the community and by BGG editors. If your group is larger than the game’s absolute maximum, the result is zero. Otherwise it measures how close your player count is to the midpoint of each ideal band: a perfect hit inside the band starts at 1.15, dropping by 0.25 for each seat you stray (scaled by the band’s width); if you sit outside the band it starts at 0.5 and fades by 0.1 per seat. Community and BGG are scored the same way, so they carry equal weight. Any negative partial scores are floored at zero, the two sources are added together, a 0.5 cushion is tacked on so decent fits don’t vanish, and the total is rounded to two decimals, producing a number up to about 2.8 and sliding toward zero as the fit worsens.

The results are assembled in the suggestions sections and then they are colored by tier. The tier thresholds adjust automatically as games or filters change.  
  
[https://docs.google.com/spreadsheets/d/1pprYmTy6ok\_MvpsZgsTL3hxR-xQbEfyYHCKHo9QgD7M/edit?usp=sharing](https://docs.google.com/spreadsheets/d/1pprYmTy6ok_MvpsZgsTL3hxR-xQbEfyYHCKHo9QgD7M/edit?usp=sharing)

Made a spreadsheet tool for recommending games from my home library. Right now it let's you select the number of players, available playtime, and desired difficulty with a few other ribbons. Would love feedback!