Flow

Connecting the dots is only half of it

Here's the thing that catches newcomers out: joining every pair of dots is not enough to win. You also have to cover every single cell in the grid. A board can look finished (all the dots linked) and still be wrong because one empty square sits in a corner with no path running through it. So stop thinking of it as drawing the shortest lines. Think of it as tiling the whole grid, where the tiles happen to be coloured paths that begin and end on matching dots.

Read the corners and edges first

Corners are the best place to start, because a corner cell has only two ways out. If a dot sits in a corner, its path is half-decided before you've drawn anything. Edge cells behave the same way, with a little more freedom.

• Don't hug: a path that runs alongside its own colour for no reason usually wastes cells another colour needed. Keep each line as direct as the fill allows.
• If two same-coloured dots sit close together, the tempting straight line between them is often wrong; the real route sends that path the long way round to mop up stray cells.
• When a cell can only be reached by one colour, that colour has to go there, full stop. Those forced cells chain together into whole routes.

Re-dragging a path erases and redraws it, so there's no penalty for experimenting: pull a line back and try a different bend whenever the fill leaves a hole.

Pick an order and stick to it

Strong players don't connect pairs in whatever order catches their eye. They run a routine: corner dots first, wall dots second, the open middle last. Corner and edge dots have the fewest options, so they hand out certainty early, and certainty is what the middle of the grid feeds on. Long-distance pairs usually claim the border, sweeping around the outside to soak up the cells nothing else can reach, while short local pairs tidy the pockets left behind.

Try it on a real board. A dot sits in the bottom-left corner and its partner is two cells to the right. The straight little line between them takes two moves and looks perfect. But look above it first. If any cell over that line can only be reached by this colour, the direct route is a trap: the real path has to climb, collect those cells, and come back down to the partner. Checking what a route leaves behind, before you draw it, is the single biggest jump from casual to competent.

Watch how your early paths sit together, too. The first three routes you place decide the character of everything after. If two of them run side by side for a long stretch, you've probably robbed a third colour of its only corridor; unwind one of them rather than forcing the rest of the board to cope.

One more habit pays off on every board: save an escape hatch. The last pair you connect has no flexibility at all, since it must use exactly the cells everyone else left behind. So keep your most flexible pair, usually the one whose dots are far apart with several possible routes, for the end, and let it snake through whatever awkward leftovers remain. Beginners connect their favourite pair first and their hardest pair last, which is exactly backwards.

From Numberlink to Flow

The underlying puzzle is a classic called Numberlink, a staple of Japanese logic magazines, where the catch has always been that every cell must be used, not just the endpoints. It reached a huge audience in 2012 when a small studio called Big Duck Games released Flow Free, and the coloured-pipe version became one of the most downloaded puzzle apps ever made. Part of that success is honest design. Each board has a single intended solution, so it never cheats you, and dragging a path feels good in a way tapping never quite does. Underneath the relaxing swipe-and-connect surface it's a genuine logic puzzle, and the fill-everything rule is what stops it from being trivial. Sit with a hard grid for a few minutes and you'll notice the game has quietly taught you to reason about space: which regions are sealed, which colour owns them, and which single bend fixes it all.