Just Roll user guide

Just Roll is a dice roller for tabletop games. You build a dice expression on a calculator-style keyboard, press Roll, and get the total with every die shown. It works entirely offline and keeps your history and favourite dice on the device.

The Roll screen

The screen has three parts, top to bottom:

The expression strip — what you are about to roll, as chips such as 2d20kh + 7. Below it, a plain-English line says what the expression does (“Roll 2 d20s (keeping the highest die) and add 7”). While the strip is empty it reads “Tap dice to start”.
The keyboard — dice keys along the top, a numpad with Clear, and the extra keys behind the arrow beside dN.
Analyze · Roll · Save — see what totals to expect before rolling, roll, or save the dice to roll again later.

Your last ten rolls appear under the keyboard, newest first, with All history at the bottom. On a tablet, or a phone turned on its side, the history has its own pane beside the keyboard instead.

Rolling dice

To roll…	Press
One d20	`d20`
Three d6	`3` then `d6`, or `d6` three times
A d20 plus 5	`d20` `+` `5`
d8 plus d6 plus 3	`d8` `+` `d6` `+` `3`
A d3 or any other size	`dN`, then type the number of sides on the numpad

Digits typed before a die set how many to roll; digits typed after + or − are a fixed bonus or penalty. d100 is on the top row.

Backspace (the ⌫ key) undoes your last key press, whatever it did, so a mistake is always one tap away from fixed. Clear (bottom left of the numpad) empties the strip; so does a long-press on backspace.

After you roll, the expression stays in the strip so Roll again is one tap away, and its chips fade. While they are faded, the next die or number starts a new roll: d20, Roll, d20 rolls a fresh d20 rather than building 2d20. +, − and the extra keys add to the roll you just made instead (d20, Roll, + 5 gives d20+5). Started a new one by mistake? Backspace brings the last roll back, all of it at once; another backspace clears it.

Roll is only enabled when the expression is complete. A key that doesn’t make sense right now — kh with no dice, for instance — is drawn with a dashed outline; tapping it gives the strip a little shake and tells you why (“Needs dice first”).

The extra keys

Tap the arrow beside dN and a sheet of modifier keys slides over the keyboard. Each applies to the dice group you just typed. Long-press any of them for a reminder of what it does.

Pressing a modifier puts the sheet away again, so you can type its number straight after (kh then 3). So does rolling, tapping the arrow again, or tapping the dimmed dice above the sheet.

Key	What it does	Example
`kh`	Keep only the highest dice. On a single die it rolls two and keeps the better one — press it again to roll three.	`d20` `kh` → `2d20kh` (best of two)
`kl`	Keep only the lowest dice. On a single die it rolls two and keeps the worse one.	`d20` `kl` → `2d20kl` (worst of two)
`dh`	Drop the highest die from the total.	`4d6` `dh` → `4d6dh`
`dl`	Drop the lowest die from the total.	`4d6` `dl` → `4d6dl` (best three of four)
`r`	Keep rerolling dice that show 1 until they don’t.	`2d6` `r` → `2d6r<=1`
`ro`	Reroll dice that show 1, once each.	`2d6` `ro` → `2d6ro<=1`
`!`	Exploding dice: every die that rolls its maximum rolls again, and keeps going while it does.	`d6` `!` → `d6!`

After pressing a modifier key you can type a number to change its value:

kh / kl / dh / dl then 2 keeps or drops two dice (5d6kh2).
r / ro then 2 rerolls anything showing 2 or lower (2d6r<=2).
! then 5 explodes on a 5 rather than the maximum (d6!5).

Numbers the dice can’t use are refused: dh and dl must leave at least one die, and r must leave at least one face that isn’t rerolled (on a d6, r then 6 would reroll forever; ro then 6 is fine).

Modifiers can be combined on one group, and Just Roll applies them in a fixed order: reroll first, then explode, then keep or drop.

Reading a result

Each roll gets a card showing the expression, the total, and a breakdown:

every die’s face, in a chip coloured to match its die key, lined up in columns: every chip in a group is as wide as the biggest number that die can roll;
dropped dice as outlines with their face struck through, after the dice that count;
rerolled dice showing the earlier value(s) alongside the one that counted;
exploded dice as a chain (6 → 6 → 2);
the arithmetic that leads to the total.

When a group has more dice than fit on two rows, the card shows the first two rows and then … show N more. Tap it to see every die in that group, and show fewer to fold it again. Tapping the dice themselves still folds the card.

Tap a card to expand or collapse it. Long-press a card for Show stats, Save… and Roll again. Rolls made from saved dice show their name on the card.

What to expect: the other side of a card

Every card has a second side showing what totals its dice produce, so you can tell at a glance whether a roll came out high, low or about average. Tap the chart icon in the bottom-left corner of an expanded card to turn it over, and the die icon to turn it back. Show stats in the long-press menu does the same, even on a folded card.

The bars show how likely each total is: the taller the bar, the more often that total comes up. The rarest totals at each end are left off so the rest stay readable; a dotted stub marks a side that goes on further.
min and max under the ends are the lowest and highest totals the dice can make. Exploding dice have no maximum, shown as ∞.
average sits under its own small tick: the total you’d get on average over many rolls.
A line marks the total you rolled, with the total itself in a small label above the chart, next to a die. If it was one of the rare totals left off the chart, the line sits at that edge and the label has an arrow pointing beyond it.

A very large expression can take too long to chart; the card then says so and shows only min and max.

Analyze (left of Roll) adds a card for your dice without rolling them, stats side up, so you can look before you roll. It says “Not rolled yet” until you roll it: press Roll (it still holds the same dice), or the Roll button on the card’s other side. The card then turns over to show the result, and stays where it is in the history.

An exploding die stops after 100 extra rolls (you’ll see “chain capped” if that ever happens). A die that keeps rerolling shows its first 8 rerolls, also marked “chain capped” if it needed more, but only the list is shortened: the face it lands on is exactly what rerolling for as long as it takes would give.

Saved dice

Saved dice are expressions you want to roll again later, with a name if you like: “Sword”, “Fire spell”, “Stats”.

Save — press the star beside Roll (or long-press a result card and choose Save…), then give the dice a name, or leave it empty. Saved dice without a name show just their dice.
Roll — tap an entry on the Saved dice tab. The roll appears in the history like any other, with the name, if it has one, on its card.
Reorder — drag by the handle on the right. With TalkBack, use the entry’s Move up and Move down actions instead.
Analyze — long-press an entry and choose Analyze to see what totals to expect before rolling it. The card carries the saved name, if any.
Rename — long-press an entry and choose Rename. Clear the name to remove it.
Delete — long-press an entry and choose Delete.

History

The History tab lists every roll, newest first, with the same cards and the same long-press menu as the Roll screen. The most recent 100 rolls are kept; the top of the list says how many there are. Rolls are grouped by session, under a header saying when each one started; a new session starts after two hours without a roll. Clear history (the sweep icon at the top of the list) deletes them all after confirming; saved dice are not affected. Single rolls can’t be deleted, so a roll you don’t like can’t quietly disappear.

Settings

Open the menu (☰) at the top left.

Keep screen on (on by default) — the screen stays awake while Just Roll is in front, so the dice are ready at a moment’s notice.
Sounds and vibration (on by default) — Roll gives a short tick and a key that can’t be pressed yet a buzz, and taps click if the phone’s touch sounds are on. Turn it off to keep Just Roll silent, whatever the phone’s settings.
Theme — Light, Dark, or follow the system. The dice colours are the same in both.

The menu also has User guide (this guide) and Take the tour, a one-minute walk through the basics: building a roll (2d20, keeping the highest, plus a bonus), reading the result, and its stats on the other side. Each step asks you to try something; Next does it for you if you’d rather just watch. It runs by itself the first time you open Just Roll; Skip tour leaves it at any point, and it won’t start by itself again.

With TalkBack

As you type, TalkBack reads the plain-English line under the strip, so you hear what you have built (“Roll a d20 and add 4”). A key that can’t be pressed right now says why when you touch it, and a new roll’s total is read out as soon as it appears.
Double-tap and hold one of the extra keys to hear what it does, and backspace to clear the strip.
Everything in a long-press menu is also in TalkBack’s actions menu: Show stats, Save and Roll again on a card, and Move up, Move down, Analyze, Rename and Delete on saved dice.
This guide’s section titles are headings, so you can move from one to the next.

Dice notation reference

Everything the keyboard builds is standard dice notation, shown in the strip exactly as you would write it. If you have seen 2d20kh or 4d6dl before, you already know it.

Notation	Meaning
`dX`, `NdX`	Roll one, or N, X-sided dice. N can be up to 100, X from 2 to 1000. `d%` means `d100`.
`khN`, `klN`	Keep the N highest / lowest (N defaults to 1: `kh` is `kh1`).
`dhN`, `dlN`	Drop the N highest / lowest.
`!`, `!N`	Explode on the maximum, or on exactly N.
`r<=N`, `ro<=N`	Reroll dice showing N or lower — repeatedly, or once each.
`+`, `−`	Add and subtract dice groups and numbers.

Limits: at most 100 dice in a group, 1000 sides on a die, and 20 terms (dice groups and numbers) in an expression; +, − and any dice key that would start another group stop there. The app catches impossible expressions before you roll and says what’s wrong, for example “Can’t keep 4 dice from 3d6”.

Wider screens

With room to spare, on a tablet or a phone turned on its side, Just Roll spreads out:

Landscape — the keyboard and Saved dice tabs on the left, the history permanently on the right. On a tablet the keys stretch to fill the height when every key fits at a comfortable size; on a phone or a smaller tablet they keep their size and scroll.
Portrait (tablets) — the keyboard above your saved dice on the left, history on the right, no tabs at all.

Everything else behaves the same as on a phone held upright.

Posted Oct 26, 2026 /justroll/user-guide