How dice.run Shows Probability Distributions

Updated

dice.run displays a probability distribution for any dice expression you enter: as you type, it computes the exact odds and shows the mean, the range, and the full distribution. This is useful when you want to know the likelihood of outcomes before or instead of rolling — for example, checking how often a 2d6+3 attack lands at least 10 damage, or comparing two damage expressions during game design. The distribution view is tied to the expression grammar, so anything the roller can parse, it can also analyze.

What the distribution view contains

According to the site, the probability panel shows three things for the expression currently entered:

  • Mean — the average result you'd expect over many rolls.
  • Range — the span of possible outcomes.
  • Full distribution — the odds of each individual outcome, not just a summary.

The heading on the page states the intent directly: "Roll dice. Know the odds." The description adds that the tool parses standard notation, rolls with full audit trails, and analyzes probability distributions.

How it updates as you type

The page describes the behavior in one line: "Enter a dice expression above. Its exact odds — mean, range, and the full distribution — appear here as you type."

So the workflow is:

  1. Type a dice expression into the input.
  2. The distribution panel recalculates immediately — no separate "analyze" step is described.
  3. Read the mean, range, and per-outcome odds for that expression.

Because it recalculates on each edit, you can iterate: change 2d6+3 to 2d6+5 and watch how the mean and the shape of the distribution shift. That makes it a comparison tool as much as a lookup tool.

Where distributions are used: Studio

The page lists "Probability distribution" as a heading and points to Studio with an "Open in Studio →" link. Studio is described as a place to "author dice programs with live distributions." The key word is live — distributions aren't a one-off report, they update alongside the program you're writing.

This matters for game design work: if you're tuning a mechanic, you can write the dice logic and see the odds change as you adjust it, rather than rolling samples and estimating.

Practical uses

  • Checking odds before a roll. Enter the expression and read the exact probability of hitting a target number or falling in a range.
  • Comparing expressions. Put two candidate damage or check formulas side by side (by editing between them) and compare means and spreads.
  • Game design. Use the live distribution in Studio to see whether a mechanic produces the spread you intend.
  • Understanding notation. Since the distribution depends on the expression grammar, seeing the output is a way to confirm the parser read your notation the way you meant.

What to keep in mind

  • The distribution is exact for the parsed expression, per the page wording — it's a computed distribution, not a sample of rolls.
  • It's driven by the expression grammar, so the docs are the reference for what you can enter. Anything outside that grammar won't produce a distribution.
  • The page also mentions community packs (for example, a D&D 5e 2024 pack with attack, damage, save, and multi-attack examples) and a roll mode switch for normal / advantage / disadvantage. These are separate from the distribution panel but relevant if you're computing odds for those mechanics.

If your goal is simply to roll and keep a record, the audit-trail rolling covers that. If your goal is to know the odds first, the distribution view is the part to use — and Studio is where it stays live while you build.