Domino Line

Eight numbered tiles, laid face up, and one goal: build them into a single unbroken line where every pair of touching halves shows the same number. A 3–5 tile can go against a 3 or against a 5, and nothing else. Both ends of the line stay open, so every tile you place is a choice of which tile and which end — and the line always has an answer, because the set was built by walking one before it was shuffled.

You get one attempt per tile plus a small margin, and an attempt is spent whether the tile lands or is refused. That is the whole game: a refusal is information you paid for, so it is cheaper to work out where a number has to go than to find out.

It runs entirely on your device: 0 network requests, works offline. No ads, no account, nothing to buy, and no betting, money or prizes of any kind.

1. Focus the board — click it, or press Tab until it is focused.
2. Choose a tile with Left and Right. The chosen tile is outlined, not just tinted, and every tile that fits an open end right now reads ✓ fits.
3. Lay it on the left end with Up, or on the right end with Down. Press Enter to lay it wherever it fits — the right end wins if both do.
4. Let the tile turn itself. You never choose which way round a tile goes: the half that matches the open number is the half that touches the line, so a 3–5 laid against a 5 reads 5–3.
5. Press F to jump straight to the next tile that fits an open end. Moving the chosen tile costs nothing; only laying one spends an attempt.
6. Watch the two open numbers. They are printed above the line and repeated on the two end buttons, so you never have to trace a long row to remember what is open.
7. Read the ends line. The board tells you which two numbers the finished line has to end on — see the first question below for why it can know that before you have laid anything.
8. Win when all eight tiles are in the line. The round ends if you run out of attempts, or if no tile left in your hand shows either open number.

How do you know a set of dominoes can be laid in one line?

Count how many times each number appears across all the halves. If you draw the set as a diagram — one dot per number, and one link per tile joining the two numbers on it — then laying every tile in a line is exactly the same thing as tracing every link once without lifting your pen. That is called an Eulerian path, and it exists precisely when the diagram is in one piece and at most two numbers appear an odd number of times. Those two odd numbers, if there are any, must be the two ends of the line; every other number appears an even number of times because the line arrives at it and leaves it in pairs. If no number is odd, the line closes into a loop and can start anywhere. This game prints the odd numbers for you on every board, which is why you can plan the ends before you plan the middle.

Is every deal actually layable?

Yes, and by construction rather than by luck. The generator never shuffles tiles and hopes. It builds a finished line first — starting at a random number and stepping to a random next number, writing down the tile it just crossed, never reusing a tile — and then hands you that line shuffled, with each tile flipped at random so the printed halves say nothing about the order. The line it walked is a complete answer, so at least one answer always exists. A second, independent solver counts how many complete lines the dealt set has, and that count is what sets your attempt margin: a set with only one way through gets the most spare attempts, and a forgiving set gets the fewest.

What happens if no tile fits either end?

The round ends immediately and is scored as a loss, with the two open numbers named so you can see what happened. There is nothing to wait for — no tile is drawn and none is coming, so a position with no legal move can only get older, not better. Ending it at once is the honest thing to do, and it is the lesson the game is built around: a dead end is never a bad deal, it is a number you spent too early. If you use both of your 4s while a 4 is still needed at an end, the line cannot reach it.

Why does a refused tile still cost an attempt?

Because otherwise there is no puzzle. If offering a tile were free you could simply try all eight tiles at both ends every turn and never think at all; the line would fall out of pure repetition. Charging for the offer makes checking a number in your head cheaper than checking it on the board, which is exactly the trade the game wants you to make. The margin above one-attempt-per-tile is small but real — between two and six extra, set by the solver — so one honest mistake is survivable and guessing is not.

Is there any money, betting or in-app purchase in this?

None, and there never will be. The tiles are numerals in boxes: no currency, no wager of any kind, no gambling mechanic, nothing to buy and no ad to watch. Your score is the base plus your unused attempts, it stays on your device, and there is nothing anywhere in the game that can be exchanged for anything.

Does it work offline?

Yes. Once the page has loaded once, the whole game is on your device — the generator, the solver, the rules and this copy. Nothing is fetched while you play, and no result leaves the device.

Can I play it with a keyboard or a screen reader?

Both. Arrows choose a tile, Up and Down lay it on the left or right end, Enter lays it wherever it fits, F jumps to a tile that fits, Esc clears the last message. The board announces how many tiles are left, both open numbers, how many attempts remain, whether the chosen tile fits either end, and the two numbers the finished line must end on. Every tile reads out its two halves as words, and fits and refusals are announced as words and drawn with a glyph, so nothing depends on telling one tint from another.

Eight tiles, halves from 0 to 6, drawn from a set in which each pair of numbers appears at most once. One rule: touching halves must match. The tile turns itself, so there is no wrong-way-round mistake to make. Attempts run from ten to fourteen depending on how many complete lines the deal has, and the margin is the solver's number, not a designer's guess. Doubles are ordinary tiles here — a 4–4 sits against a 4 and leaves a 4 open — and there is no draw pile, no passing and no second player.

Route Plan is the other path-planning puzzle here: it walks a grid to a target total rather than tracing every link once. Fence Loop is the closest relative in shape — one closed loop that satisfies every clue — and Card Ladder is the other game about spending a piece in the wrong order and being unable to get it back.

Bookmark this page (Ctrl+D, or ⌘D on Mac) or install the app — it works offline the next time you need it.