Crit Mechanics

FlowDice supports two crit systems, selectable per-roll via notation suffixes. They are mutually exclusive on a single dice expression.

Normal Crit (c)

Doubles the number of dice rolled. The standard 5e crit rule.

Input	Resolves To
2d6c	4d6
d8c	2d8
d12c+5	2d12+5 (modifier unaffected)

Perkins Crit (C)

Maxes one set of damage dice and rolls them again. Named for DM Chris Perkins’ house rule. Guarantees at least maximum single-roll damage.

Input	Resolves To
2d6C	12 + 2d6
d8C	8 + d8
d12C+5	12 + d12 + 5

Key Principle: Crits Affect Dice, Not Static Bonuses

Static modifiers (+3, +5, etc.) are always outside the crit scope and are applied once. Only the dice portion is doubled (normal) or maxed+rerolled (Perkins).

Crit Scope via Grouping

Parentheses control what the crit applies to:

(d8(<smite>?+2d8))(n20?c)+3

If smite is active and a nat 20 is rolled, the c doubles everything in the first group: d8 becomes 2d8, 2d8 becomes 4d8. The +3 stays outside.

Conditional Crits in Flows

Crits are applied conditionally using trigger syntax:

d20+5->d8(n20?c)+3

Normal crit only if nat 20.

d20+11->2d6(n20?C:(n[18..19]?c))+5

Perkins crit on nat 20, normal crit on nat 18–19 (Champion fighter).

Note: Save-Based Spells Don’t Crit

Spells that require saving throws (like Fireball) cannot critically hit. Crits only apply to attack rolls. Crit modifiers should only be used on damage expressions chained from attack rolls.

See also: Normal Crit, Perkins Crit, Flows, Notation Spec