Tic-Tac-Toe Streak Strategy: How to Beat Each Computer Level

Updated October 2026

Everyone knows how tic-tac-toe works, and most people know that two careful players always draw. What makes this version interesting is the scoring: you are playing for a winning streak against a computer that changes its style as the streak grows. It starts out careless, becomes solid but predictable, and finally plays almost perfectly. Each stage needs a different plan. This guide explains how each stage behaves, the opening that beats the middle stage every single time, and why streaks beyond five get rarer with every round.

The rules of a streak

You are X and you always move first, in every round. Tap an empty square and the computer answers after a short pause. A round you win adds one to your streak, and a drawn round or a lost round ends the game. After a win the next round starts on its own a moment later.

Two details are worth knowing. First, the game-over card, with its Save score button for the Hall of Fame, appears whenever a run ends, after a loss or a draw, as long as your streak is above zero. Second, pressing New while you have a streak ends the run on the spot and shows the same card, so you can stop and save whenever you like. Your best streak on this device is updated whenever a run ends.

Stage one: the careless computer

While your streak is zero or one, the computer plays loosely. It always takes a winning square if it has one. When you threaten to complete a line, it blocks only 70 percent of the time. Otherwise it simply picks an empty square at random, with no preference for the centre or corners.

That makes double threats very strong, and even a single threat has a real chance of being left open. We worked out the best possible play against this stage by exhaustive calculation over every position. Opening in a corner gives the highest chance to win a round, about 95 percent, and opening in the centre about 89 percent. With correct play the careless computer can never beat you, so the rounds you do not win are draws, and since a draw ends the run, the corner's higher win chance matters.

The plan is simple: take a corner, and on every move first look for your own winning square, then for a computer threat you must block, then for a move that creates two open lines at once.

Stage two: the predictable computer

From a streak of two up to four, the computer tightens up. It still takes any winning square, it now blocks every threat without fail, and when there is nothing to win or block it chooses by a fixed order of preference: the centre if it is empty, otherwise a random corner, and only if no corner is left, a random edge.

That preference is the weakness. Our exhaustive calculation shows that this stage loses every single round to one line of play, and it is the classic corner trap:

1. Open in a corner. The computer, preferring the centre, always replies in the centre.
2. Take the corner diagonally opposite your first one. There is no threat to answer, so the computer picks one of the two remaining corners.
3. Its new corner and the centre now form a line aimed at the last free corner, so you must block there. That block is also your winning move: the three corners you hold give you two open lines along two sides of the board.
4. The computer can only block one of them. Complete the other.

The trap works because the computer prefers corners over edges. Against a careful human the correct reply at step two is an edge, which defuses the fork. Opening in the centre, by contrast, gets you nowhere at this stage: the calculation found no winning line against a computer that answers with a corner and blocks everything.

Stage three: the nearly perfect computer

Once your streak reaches five, the computer searches every possible continuation of the game before each move. Normally it picks the move with the best guaranteed result, preferring quick wins and slow losses, and chooses at random among moves that are equally good. But it is not flawless. On each move where a worse option exists, it slips with a chance of 30 percent at a streak of five, and that chance shrinks to 85 percent of its previous value with every further win, to about 13 percent at ten, 6 percent at fifteen and 3 percent at twenty, without ever reaching zero. A slip is always a move that turns the round into a forced win for you. If it never slips, the round is a draw, and a draw ends your run.

So there is no fixed ceiling, but the odds fall quickly. With the best possible play against this computer, our exact calculation over every position gives a 76 percent chance of winning the round at a streak of five, 44 percent at ten and 10 percent at twenty. Only about 3.5 percent of runs by a flawless player get past a streak of ten, and such a player's expected final streak is about six.

Defence still matters, because a loss ends the run just as a draw does. Before every move, check that you are not leaving the computer a square that creates two threats at once, because it will almost always find it. Whenever the computer has two in a row, block immediately. And whenever it slips, stop and find the fork that punishes it.

Recognising forks

A fork is a single move that creates two lines with two of your marks and an empty third square. Your opponent can only fill one square per turn, so one of the lines survives. Nearly every win against the first two stages comes from a fork, and nearly every loss to the third stage comes from allowing one.

• Corner forks use three corners. They usually appear when your opponent has the centre and takes a corner rather than an edge.
• Centre forks combine the centre with a corner and an edge, and they appear when your opponent places a mark on an edge too early.
• Forced forks are the most satisfying: a block you are forced to make turns out to be the fork itself, exactly as in the corner trap.

When it is your opponent's turn, look at the board from its side. If any single empty square would give it two open lines, take that square yourself, or create a threat of your own that it must answer first.

Putting it together

A complete run looks like this. In the first two rounds, take a corner and play for forks. The careless computer will often hand you a win, and if it does not, the draw ends the run, so make the most of its mistakes. From a streak of two, use the corner trap every round: corner, opposite corner, block the last corner, win. Three rounds later you are at five. From there each round is a draw unless the computer slips, so play every round out, punish each slip with a fork, and expect a draw to end the run sooner or later.

Whenever a run ends, by a loss, a draw or pressing New, the game-over card offers to save your streak. The Hall of Fame uses a new board for these rules, separate from the scores set under the old rules, when draws kept a streak alive and five was the most anyone could reach.