A 15×15 board has 225 intersections and four directions through each. Looking at all of them is impossible, so the skill is knowing where to look.
Window scanning
Any five consecutive intersections in a line is a potential five. So instead of looking at stones, look at windows of five. A window containing four of one colour and one gap is an immediate threat. A window with three and two gaps is a developing one.
This reframing catches broken threes automatically, because the window does not care whether the stones are adjacent. XX.X. and .XXX. both register as three-in-five.
The scan order
- Windows containing four of my stones — can I win now?
- Windows containing four of theirs — must I block now?
- Windows containing three of mine with both ends open.
- Windows containing three of theirs with both ends open.
- Intersections where two of my developing lines cross.
- Intersections where two of theirs cross.
Working in this order means you never miss an immediate win or loss, which is where most casual games are decided.
Counting open ends
For any line of three, the number of open ends decides urgency. Two open ends means it becomes an open four next move and must be answered. One open end means it becomes a simple four, which is blockable later. Zero means it is dead.
Check the ends before spending a stone. A lot of defensive moves are played against lines that were never going to reach five.
Finding crossing points
A crossing point is an empty intersection that lies on two different lines where the same player already has stones. These are where combinations happen, for both sides.
The fast way to find them: look at each of your opponent's stones and note which directions it is developing in. Where two development directions meet at an empty point, that point matters. It is worth occupying even with no immediate threat visible.
Look at the stone they just played
The most recent move tells you their plan. Before anything else, ask which lines that stone joined and where those lines are heading.
Reducing the search area
Almost every relevant move in gomoku is within two intersections of an existing stone. Points further away cannot contribute to any line for several moves. That cuts the real search space from 225 intersections to perhaps thirty, and it is exactly how the computer opponent here narrows its own search.
Building the habit
For a few games, force yourself to say the scan out loud in order — four of mine, four of theirs, threes, crossings. It is slow and it feels mechanical. After a handful of games the ordering becomes automatic and the board starts to look like a small number of important points rather than a field of stones.
This is what separates players who lose to combinations from players who see them coming: not calculation, but a repeatable way of looking.