Marble sort puzzles: reading the conveyor before it jams

Space is the score, colour is just the label

Every board is the same three parts: trays of marbles at the top, a moving conveyor in the middle, and a row of colour boxes below. Tap a tray to release its next marble, watch it tumble down onto the belt with real rolling physics, then send it into the box that matches. Each box holds a small set of one colour; complete a set and the box clears with a pop, freeing room for the next rush.

Read that loop again and notice what is missing: nothing about the marbles themselves is hard. Any single marble is trivially placeable if there's an open box of its colour. The difficulty is entirely in what happens between drops — marbles waiting for a home, taking up belt slots, narrowing the room you have to work in. Belt space is the only resource in the game, and every tap on a tray spends some of it.

So the question before each tap is never “which colour do I want”. It is “do I have somewhere to put this right now, and if not, can I afford to let it circle”. A good run of Rainbow Sort looks slow from the outside. The players who lose are the ones tapping constantly.

Commit a box to a colour, then feed it

The first real decision on any level is which colours to open boxes for. An unfinished box is wasted space — it is holding a partial set that isn't clearing anything and isn't giving you room back. Two half-filled boxes are strictly worse than one full box and one empty one, even though they hold the same number of marbles.

That means committing early and following through. Open a box for a colour, then keep feeding that colour until the set completes, rather than spreading marbles thin across four colours and finishing none of them. The moment a box completes, clear it — that pop is your room to breathe, and delaying it while marbles keep arriving is how a comfortable board tightens into a bad one.

There's a wrinkle worth watching: colours run out. When a colour is nearly exhausted, finishing its set retires that box for good, which is the cleanest kind of space you can buy. Late in a level, a colour with two marbles left on the board is usually a better target than a colour with nine, even though nine feels more urgent.

Don't dump a tray onto a crowded belt

The single most common way to lose is a burst of taps — emptying a tray because the marbles are there and the tapping feels productive. On an empty belt that's fine. On a belt already carrying marbles with no open matching box, it is how a level ends two seconds later.

Treat the trays as taps you turn on and off, not as queues to drain. Hold the flood when the conveyor is crowded, place what's already circling, clear a box, and only then open the tap again. Nothing punishes you for waiting; the belt keeps moving whether or not you drop anything new onto it, which means patience is free and haste is not.

When the belt does get tight, prioritise the colour with the most marbles circling. That's counter-intuitive if you're chasing completed boxes, but the goal in a tight spot isn't to finish sets — it's to get the marble count down, and the crowded colour is where the volume is.

Planning two or three drops ahead

Early levels use a handful of colours and a patient belt, and you can play them reactively without ever getting into trouble. Later boards add more colours, a faster conveyor and tighter box counts, and that combination is what forces actual planning: with a quick belt, the marble you drop now arrives while you're still dealing with the last one.

The habit that carries you through is looking at the trays before you tap, not after. Knowing that the next two marbles from a tray are a colour you have no box for changes whether you want to open that tray at all. Planning ahead in a sorting puzzle isn't about calculating lines — it's about not creating a problem you'll have to solve in three seconds.

There are two modes, and they reward this differently. Classic gives you a fixed set of marbles per level and asks you to clear them all, so it has a clean finish and a solvable shape you can plan against. Endless keeps the marbles coming and speeds the belt up until you drown — there the plan is simply to never let the circling count creep up, because in Endless you don't get to outlast the pressure, only to manage it well for longer.

What transfers from ball sort and water sort — and what doesn't

If you came here from ball sort or water sort, the family resemblance is real. It's the same itch: mixed colours in front of you and a brain that refuses to leave them mixed. The instinct to guard your free space transfers perfectly, because that is the shared skeleton of both games. In flask-style sorters the free space is an empty tube; in Rainbow Sort it is an open belt slot and an uncommitted box.

What does not transfer is the pause button. Tube sorters are static — the board waits while you think, and undo lets you test a line and roll it back. Rainbow Sort's conveyor is moving with proper physics, so the cost of thinking too long is that the belt fills while you do it, and the cost of thinking too little is the same. Timing joins the puzzle as a second axis.

That's the whole difference in one line: ball sort strategy asks which colour goes where, and marble sort asks that plus when. If you find you enjoy the sorting but not the clock, the static version of the itch is a click away — see below.

Play Rainbow Sort free in your browser

Rainbow Sort runs on crokocat with no download and no sign-up. On desktop you click a tray to drop a marble and click a box to send it there; on mobile it's the same two taps, and the board is built full-canvas so it fills the screen on phones and tablets alike. Progress is remembered between visits, so a level you abandon at a bus stop is still there in the evening.

If the moving belt is the part you'd rather do without, Gem Sort on the same portal is the classic flask-and-pour version: gems land only on their own colour or in an empty flask, matching gems on top travel together, and every level is checked by a solver before you see it, so there are no dead deals. Undo there is free and unlimited — which makes it the better place to practise the pure planning half of sorting, before bringing it back to the conveyor.

Frequently asked questions

Play it here

• Rainbow Sort — Roll every marble into its color
• Gem Sort — Sort the sparkle