Difficulty tuning uses sliders for each tier. Medium requires minimum subset deductions; Hard adds overlap deductions plus subset moves. Extreme demands what-if deductions and chain depth (capped by MAX_WHAT_IF_FIRINGS). Insane exceeds Extreme's cap and requires either-way deductions — pivots where both hypotheses survive yet agree on another square.

Every grid is solved end-to-end by the logic engine powering in-game hints. It plays through deduction by deduction, taking the simplest move, recording forced techniques. Five tiers named after hardest technique: Basic → Easy (single clue settles squares), Subset → Medium (two clues compared), Overlap → Hard (shared squares with min/max bounds), What-if → Extreme (hypothetical placement, watch clue break, contradiction proves opposite), Insane (chains longer than Extreme's cap, plus either-way technique).

0–100 score places grid in tier bands: Easy 4–19, Medium 20–39, Hard 40–59, Extreme 60–79, Insane 80–100. Bands never overlap. Estimated time sums work: ~1s/square routine, ~2s/basic, ~14s/subset, ~26s/overlap, ~15s+10s/step/what-if, ~35s+step/either-way. Zero clues: Easy/Medium 1–2 zeros, Hard exactly one, Extreme/Insane none. Generator protects needed zeros, rejects invalid grids. Sliders tighten requirements; each click tries 90 candidates, serves closest match flagged if none fits.