Damage & Attacks

The expression parser supports several specialized expression types for combat.

Expression Types

Expressions fail with an error payload when they cannot be parsed.

Parse error at 1:13 - found token '+' ...
Lexing error at 1:5 - found token '$' ...

Basic Expression

Returns a numeric value:

str + prof           # Attack modifier
8 + prof + int       # Spell save DC base
2 + 3                # Simple math

Dice Expression

Includes dice rolls:

2d6                  # Just dice
2d4 + str            # Dice plus modifier
4d8 + 12             # Dice plus flat bonus

Damage Expression

Includes damage type(s):

2d6 slashing                    # Single damage type
2d4 + str fire                  # Damage with modifier
2d6 fire + 1d8 cold             # Multiple damage types
3d8 + con necrotic              # Necrotic damage

Save Expression

Defines a saving throw DC.

Format: DC <expression> <SAVE_TYPE>

DC 8 + prof + str STR           # Strength save
DC 8 + prof + dex DEX           # Dexterity save
DC 8 + prof + con CON           # Constitution save
DC 8 + prof + int INT           # Intelligence save
DC 8 + prof + wis WIS           # Wisdom save
DC 8 + prof + cha CHA           # Charisma save

Tip

The standard formula for spell save DCs is 8 + proficiency + spellcasting modifier.

Hit Expression

Defines an attack roll bonus.

Format: Hit <expression>

Hit str + prof                  # Melee attack (Strength)
Hit dex + prof                  # Ranged attack (Dexterity)
Hit str + prof + 2              # Magic weapon (+2)

Note

Hit expressions automatically include a d20 in the roll.

Supported Damage Types

Type	Description
acid	Acid damage
bludgeoning	Bludgeoning damage
cold	Cold damage
fire	Fire damage
force	Force damage
lightning	Lightning damage
necrotic	Necrotic damage
piercing	Piercing damage
poison	Poison damage
psychic	Psychic damage
radiant	Radiant damage
slashing	Slashing damage
thunder	Thunder damage
hp	Healing
thp	Temporary hit points

Multi-Damage Expressions

You can combine multiple damage types in a single expression:

2d6 + str slashing + 2d6 fire

This creates a damage roll with:

• 2d6 + STR modifier slashing damage
• 2d6 fire damage

The parser tracks each damage type separately, allowing for proper resistance/immunity calculations.

Output Structure

Damage Output

{
  kind: "damage",
  damage: {
    fire: { avgResult: 7, dice: { d6: {...} } },
    cold: { avgResult: 9, dice: { d8: {...} } }
  }
}

Save Output

{
  kind: "save",
  avgResult: 15,           // The DC value
  saveType: "DEX",         // Which save
  expression: "DC 8 + prof + int DEX"
}

Hit Output

{
  kind: "hit",
  avgResult: 7,            // Attack bonus
  dice: { d20: {...} },    // Always includes d20
  expression: "Hit str + prof"
}