Compare two options for one turn of combat. Each option is a list of attacks: give each attack its bonus to hit and its damage dice, pick the rules, and set the target's Armor Class. The odds are exact, worked out from every d20 face and every damage die, and everything below updates as you type. Reset brings back this simple start; the Example menu has worked comparisons.
One bar per damage total. The bars at 0 are the turns where every attack misses; when they would dwarf the rest they are cut (//) and their true height is written on top.
Read off the line at a monster's hit points: that is the chance this turn drops it.
Line is the average; the band holds the middle 80% of turns (10th to 90th percentile).
Same AC axis. A turn that deals nothing is the outcome players remember.
General. Every attack is a d20 plus its bonus to hit against the target's Armor Class (AC). The odds come from trying all 20 faces of the die and every damage die, so they are exact, not simulated. "Roll 2, keep higher" (fortune, advantage) and "roll 2, keep lower" (misfortune, disadvantage) change which face counts. "Once per turn, first hit" damage is added to the first attack of the turn that hits, and to no other. The bars at 0 damage are the chance that every attack misses.
Pathfinder 1e / D&D 3.5. A natural 20 always hits and a natural 1 always misses. A hit on a face in the threat range is a threat; it becomes a crit if a second roll at the same bonus (plus any confirm bonus) also hits. A crit rolls weapon damage, modifiers included, as many times as the multiplier; precision damage and "on crit, not multiplied" dice are added once. Sneak attack applies to every qualifying hit, so type it into the damage of each attack. A hit deals at least 1 (our reading). The confirmation roll uses the same "roll 2" setting as the attack (our assumption). Type each attack at its own bonus to hit, iteratives included.
Pathfinder 2e. Beat the AC by 10 to crit, miss it by 10 to critically fail; a natural 20 is one step better and a natural 1 one step worse. A hit deals at least 1 damage; a crit doubles that, then adds the deadly die. Fortune and misfortune together cancel, so pick neither. The multiple attack penalty (MAP) is applied for you, set once per option: -5/-10 (agile -4/-8), or against a ranger's hunted prey with Flurry -3/-6 (agile -2/-4) and with Masterful Hunter -2/-4 (agile -1/-2). Sneak attack applies to every Strike against an off-guard target, so type it into each attack's damage; "once per turn" fits the ranger's Precision edge (first hit each round). The Action menu covers two fighter feats: Exacting Strike, a press that cannot be your first attack, does not count toward MAP if it fails or critically fails; Vicious Swing (Power Attack before the remaster) takes two actions and counts as two attacks, so type its extra weapon die into the damage.
D&D 5e. A natural 1 always misses, and a face in the crit range (20, or 19-20 for a champion) always crits. A crit rolls every damage die twice, sneak attack included, and adds modifiers once. Sneak attack is once per turn: use the option's "once per turn" box. Type each attack at its own bonus to hit.