Two modes
A player tray. A designer workbench.
Player mode is the quick cast — a single expression, a big number, and a tumble animation that lands on face-up dice. Designer mode splits the view: build two expressions side by side, watch the distributions, read the interpretation ribbon, and see where the math actually differs before you pick a ruleset.
The notation it reads
Pools
2d6, 1d20, 4dF (fudge), 1d% (d100 alias).
Keep / drop
4d6kh3 keep highest 3 (stat gen). 2d20kh1 advantage. 2d20kl1 disadvantage. 2d6dl1 drop lowest.
Exploding
3d6! — re-roll any max face and add it to the same pool.
Modifiers & custom dice
Add flat modifiers with +3 or -2. Forge custom dice with named faces, reference them as d$name in any expression.
Seeded rolls
Lock a seed for deterministic roll sequences — useful for reproducing a session or debugging a house rule.
Why exact, not just simulated
The distribution is the ruleset.
Most dice tools run a Monte Carlo: they roll ten thousand times and show you the histogram. That’s fine — but for small pools the true distribution is finite and knowable. This tool computes it exactly by convolution whenever the outcome space is small enough, and falls back to simulation only for pools too large to enumerate.
The difference matters when you’re tuning a game. “Does advantage on a d20 really feel like +3.3?” is a question the exact curve answers without noise.
If this helped, keep it free for someone else.
Supporters are why there’s no signup wall, no premium tier, and no “unlock with pro” buttons.