Dice Formulas & Customization

Read this first (no programming required)

• Formulas are simple, readable expressions (like 2d6+3).
• You can type a formula, roll it, and click “Save Formulas” to keep it for later.
• Where to find the buttons:
  • Mobile: “Save Formulas” and “Manage Formulas” are below the text field.
  • Desktop: they’re above the text field.
• Save stores whatever is currently in the text field and lets you name it and add a description. Manage lets you import, export, rename, reorder, and delete.

Tip: To save, you only need the formula text—no need to understand every option below. Come back here when you want to do something more advanced.

Basics cheat sheet

• Roll dice: XdY (e.g., 2d6, 1d20, 1d% for d100)
• Special dice: 1D66 (uppercase D), 4dF (Fate dice), custom faces: 2d[2,3,5,7]
• Math & grouping: +, -, *, parentheses ( ) (division is not supported)
• Keep / Drop: kh keep highest, kl keep lowest, -H drop highest, -L drop lowest (e.g., 3d20kh2, 4d6-L)
• Explode / Compound: ! (explode), !! (compound), add o for once: !o, !!o (e.g., 4d6!, 5d10!!o>=8)
• Reroll: r (reroll matches), ro (reroll once) (e.g., 4d4r<=2, 4d4ro<2)
• Count / Score:
  • # returns a count (discards individual dice results): 6d6#>=5astro
  • Metadata counters keep dice results and record counts in metadata: #s, #f, #cs, #cf (e.g., 6d6 #f<=2 #s>=5 #cs6 #cf1)
• Clamp (cap): C< and C> (e.g., 4d20 C<5, 4d20 C>15)

Order and precedence gotchas

• Order matters with counters and keep/drop. If you do 2d20 kh #cf #cs, the low die is dropped before counting. If you want to count all rolled dice first, write 2d20 #cf #cs kh.
• Drop/filter operators bind tighter than arithmetic. (5d6+5d10)-L2 drops from the combined pool; 5d6+5d10-L2 drops only from the d10s.
• Use uppercase D66 (lowercase d66 is a 66‑sider, not D66).

Patterns you’ll use a lot

• Advantage / Disadvantage: 2d20kh+MOD and 2d20kl+MOD
• Best / Worst of N: NdXkh1 or NdXkl1 (e.g., 3d6kh1)
• Ability scores (4d6 drop lowest): 4d6-L
• Explode once vs. freely: 4d6!o (explode only once) vs 4d6! (repeat)
• Compound (Shadowrun/L5R‑style): 5d6!! or thresholded 5d6!!>=5
• Threshold successes: NdX#>=TN (e.g., 6d6#>=5)
• Reroll once vs. repeat: ro vs r (e.g., 4d6ro1 vs 4d6r1)
• Keep/drop across combined pools: (1d8!!+1d6!!) kh (Savage Worlds trait + wild die)

System starting points (quick recipes)

These examples give you solid starting formulas. Some systems use custom symbol dice—those are noted as “Not supported”.

D&D 5e / Pathfinder 2e

• Attack/check: 1d20+MOD
• Advantage/Disadvantage: 2d20kh+MOD / 2d20kl+MOD
• Ability scores: 4d6-L
• Crits: roll double damage dice manually (e.g., 2d6 → 4d6)

Powered by the Apocalypse (PbtA)

• Core move: 2d6+STAT → interpret 10+, 7–9, 6- manually

Fate Core

• Fate dice: 4dF (already supported)

Blades in the Dark

• Pool take highest: Nd6kh1 (e.g., 3d6kh1)
• Spot crits (two 6s): add Nd6#=6 to count sixes alongside your roll

Shadowrun (hits & glitches)

• Hits: Nd6#>=5
• Track 1s for glitch rules: add Nd6#f=1

Savage Worlds (trait + wild die)

• Roll both, keep highest: (TRAIT!! + 1d6!!) kh + MOD
• Raises (+4) are interpreted manually from the total

Vampire: The Masquerade (V5)

• Successes: Nd10#>=6
• Track 10s: add Nd10#=10 (critical pairs/impacts require table rules)

Call of Cthulhu 7e

• Roll-under: 1d100 vs skill
• Bonus/Penalty dice: handle as a two‑step manual method (tens die replacement not encoded)

Cypher System

• Task roll: 1d20+MOD (step/difficulty remains narrative)

Warhammer/40K‑style d6 pools

• Hits/wounds: Nd6#>=TN (set TN for your table)

Dungeon Crawl Classics (dice chain)

• Odd dice sizes are fine: 1d7, 1d16, 1d24, 1d30

Lancer (accuracy/difficulty)

• Accuracy: 1d20 + (Xd6kh1) + MOD
• Difficulty: 1d20 - (Xd6kh1) + MOD

Year Zero Engine (Free League: Alien, Forbidden Lands, Vaesen, etc.)

• Three colored pools (base/skill, stress, gear): roll each pool separately to keep counts distinct.
• Successes: Nd6#s=6 on each pool; track 1s on stress/gear with #f=1.
• Push (reroll once, lock 6s and 1s): add ro<6 ro>1 to reroll only 2–5 exactly once, e.g., Nd6 ro<6 ro>1 #s=6.
• Limitations: color tagging isn’t encoded in a single expression; roll each color as its own line. Panic/breakage resolution remains table‑side.

The One Ring 2e (approximation)

• Roughly: 1d12 + Nd6
• Notes: Gandalf/Eye and Tengwar sixes are symbol effects; treat specials manually

Legend of the Five Rings

• AEG 1e–4e (Roll & Keep, exploding 10s): Xd10!!khY
• FFG/Edge 5e (symbol dice): Not supported

Genesys / FFG Star Wars (narrative dice)

• Uses custom symbol dice: Not supported

Ironsworn / Starforged

• Action roll: 1d6+MOD vs two challenge dice 2d10 → compare manually (beat both=Strong Hit; one=Weak Hit; none=Miss).
• Progress moves: roll 2d10 vs current progress value (0–10) and compare manually.

Starter downloads

Download sample Saved Formulas for popular systems that are ready to import. Use Manage Formulas → Import to merge them into your list. See the Downloads section at the bottom for files.

Important: If you manually drop a file in place rather than importing, name it exactly saved_formulas.json. The Import flow accepts any filename.

Save, load, import, export (UI recap)

• Mobile: “Save Formulas” and “Manage Formulas” are under the formula text field.
• Desktop: both appear above the text field.
• Save adds the current formula to your Saved list and opens a dialog to name/describe it.
• Manage lets you import, export, reorder, rename, and delete.
• Import allows merging or replacing—export first if you want a backup.

Troubleshooting & gotchas

• My counts look off with advantage
  • Put counters before keep/drop: 2d20 #cf #cs kh.
• 4d6-L2+2 didn’t do what I expected
  • Drop binds tighter than +. Use parentheses for aggregate: (4d6-L2)+2.
• My D66 looks wrong
  • Use uppercase: 1D66.
• I need exploding “once”
  • Use !o (explode once) or !!o (compound once).
• I want to keep the total but also know successes/failures
  • Use metadata counters: #s/#f/#cs/#cf so rolls remain visible and counts are recorded in metadata.

Next steps

• Save your favorite expressions: see “Saving and Managing Dice Formulas”.
• Share and maintain a portable list: see “Formula Schema”.

Syntax engine and docs

The roller is powered by Adventuresmith’s dart_dice_parser. For the full grammar and additional examples, see: https://pub.dev/packages/dart_dice_parser

See a problem?

Help me keep this page and content up-to-date! If you see a problem, please report it: support@jasonholtdigital.com