Quick answer
Two players alternate placing one stone on an empty point. The first valid horizontal, vertical or diagonal line wins. ChessPlayX defaults to Caro: exactly five stones, with at least one end unblocked. A board edge blocks an end. Standard also needs exactly five; Freestyle accepts five or more.
- Players
- 2
- Board
- 15 × 15
- First move
- Black (X)
- Winning line
- A valid line of five
- Draw
- Full board, no winner
What is Caro?
Caro is a two-player alignment game. Stones stay where they are placed: they do not move, capture or disappear. Build your own lines while preventing your opponent from completing theirs.
Gomoku, five-in-a-row and paper Caro
Gomoku is the Japanese name; the game is also known as Wǔzǐqí in Chinese and Omok in Korean. Vietnamese paper Caro uses X and O inside squares. Here X represents the first player's black stones, and O the second player's white stones. The chosen rules matter more than the drawing style.
The board and the stones
ChessPlayX uses a 15 × 15 board: 225 playable points. Stone boards use intersections; paper boards use squares. Star points help orientation and have no scoring value. A central opening is useful, but is not compulsory in the three regular modes here.
| Board | Board edge | Typical use |
|---|---|---|
| 15 × 15 | Fixed edge | ChessPlayX, tournament Gomoku and Renju |
| 19 × 19 | Fixed edge | Go boards reused for five-in-a-row; some Omok and Connect6 games |
| Squared paper | Expandable | Casual X/O play; agree on the boundary and winning rules first |
How to play, step by step
Choose the rules and time control
Agree on Caro, Standard or Freestyle before starting. Check whether exactly five is required and whether blocked ends matter.
Start with an empty board
Black (X) plays first. White (O) follows. There are no pre-placed stones in a regular game.
Place the opening stone
Any empty point is legal in these three modes. Starting near the centre leaves room to develop in every direction.
Alternate one placement each
Choose an empty point. You cannot replace an occupied point, move a stone, capture or pass in these ChessPlayX modes.
Attack and defend
After each move, inspect the horizontal, vertical and both diagonal lines. Look for the opponent's immediate win before building your own threat.
Finish on a valid winning line
The game ends as soon as a line meets the selected rules. If every point is occupied and no one has won, the game is drawn.
What counts as a win, a loss or a draw?
The stones must be consecutive on one straight line. A gap or an opposing stone breaks the line. Count the entire uninterrupted row; six stones are not a separate five under exact-five rules.
Win
Create a valid line before your opponent. The selected rules determine whether a blocked five or an overline qualifies.
Loss
Your opponent completes a valid line first, you resign, or your time expires in a timed game.
Draw
A full board without a winner is a draw. Where a draw offer is available, both players must accept; a non-winning five does not itself end the game.
Three ways to decide the winning line
These modes differ in two questions: does a row longer than five win, and can a five win with both ends blocked?
Caro
Exactly five, with at least one unblocked end. An opponent's stone or the board edge immediately beyond the row blocks that end.
Standard
Exactly five wins, even with both ends blocked. Six or more consecutive stones do not win.
Freestyle
Five or more consecutive stones win. Blocked ends do not change the result.
The same line, three results
Five with two open ends
- Caro: Win
- Standard: Win
- Freestyle: Win
All three modes count this line as a win.
One end blocked
- Caro: Win
- Standard: Win
- Freestyle: Win
One open end is enough under Caro rules.
Both ends blocked
- Caro: No win
- Standard: Win
- Freestyle: Win
Caro does not count this five; Standard and Freestyle do.
An edge and an opposing stone
- Caro: No win
- Standard: Win
- Freestyle: Win
The left edge is a real board boundary. Together with White it blocks both ends.
Six consecutive stones
- Caro: No win
- Standard: No win
- Freestyle: Win
This overline wins only in Freestyle among these three modes.
Paper Caro conventions vary. This guide uses the ChessPlayX Caro rules: exactly five, and the board edge counts as a block. A non-winning row remains on the board and play continues.
Practice board: try the rules now
Control both colours on this smaller 11 × 11 board. Choose a position, play at a green ring and switch rules to compare the result. The practice uses the same game rules as regular play.
Loading the practice board…
Balancing the first move: Renju
The first move is an advantage. Renju balances play by restricting Black: the first stone is central; Black needs exactly five, while White also wins with an overline. Tournament openings add further choices and restrictions.
Double-three (3–3)
A Black move creating two genuine open-three threats is normally forbidden. A three must be able to become a legal straight four; apparent threes that require a forbidden continuation may not count. RIF rules define these recursive exceptions.
Double-four (4–4)
A Black move creating two distinct fours through the new stone is normally forbidden. Each four must have a point that completes an exact five.
Overline
Six or more consecutive black stones are normally forbidden. White has no corresponding restriction and wins with five or more.
An exact five on the same move
Under RIF rule 9.2, Black's forbidden-pattern loss applies only when the move does not also make an exact five. A six-stone row is not itself an exact five. Consult the event's rules for claims, clocks and opening procedures.
The marked points illustrate simple forbidden patterns, not a complete Renju adjudicator. ChessPlayX's regular Caro, Standard and Freestyle games do not enforce Renju forbidden moves.
Opening rules: Pro, Swap and Swap2
Pro and Long Pro
Pro starts with Black at the centre. Black's second stone, move 3, must lie outside the central 5 × 5 square; White's first stone is unrestricted. Long Pro excludes the central 7 × 7 square instead.
Swap
The first player places Black, White, Black. The other player chooses a colour. The player assigned White then makes move 4. Offering the choice discourages a one-sided setup.
Swap2, step by step
A places three stones
Player A places Black, White, Black on three empty points.
B chooses or extends
Player B chooses Black or White, or adds White then Black and lets A choose a colour.
White continues
After colours are assigned, White plays move 4 or move 6. Players then alternate normally. RIF Gomoku uses the exact-five winning rule.
These are opening conventions for learning about tournament play. They are not additional selectable opening modes in ChessPlayX's regular Caro game.
Comparing related games and variants
The first three rows describe the available modes here. Renju, Omok and Connect6 introduce other conventions; check the organiser's rules before playing.
| Variant | Board | Winning line | Longer row | Both ends blocked | Other conditions |
|---|---|---|---|---|---|
| Caro | 15 × 15 | Exactly 5 | No win | No win | An edge counts as a block |
| Standard | 15 × 15 | Exactly 5 | No win | Win | — |
| Freestyle | 15 × 15 | 5 or more | Win | Win | — |
| Renju | 15 × 15 | Black: exactly 5; White: 5 or more | Black: normally forbidden; White: wins | Win | Black's forbidden patterns; tournament opening |
| Omok | 15 × 15 / 19 × 19 | Exactly 5 | Depends on the agreed rules | Depends on the agreed rules | Often restricts double-threes; conventions vary |
| Connect6 | 19 × 19 | 6 or more | Win | Win | Black opens with 1 stone, then 2 per turn |
Connect6
Black places one stone first; each later turn places two. The target is six or more in a row, commonly on a 19 × 19 board. It is a separate game.
Omok
The Korean five-in-a-row tradition often uses a 15 × 15 or 19 × 19 board. Restrictions on double-threes and overlines depend on the agreed rules.
Expandable paper Caro
If the board can expand, there is no fixed edge in that direction. Agree whether the paper boundary counts as a block and whether overlines win.
Tic-tac-toe
A different game: a 3 × 3 board and a target of three. With perfect play by both sides, it is a draw.
Basic patterns to recognise
The green rings mark candidate moves. Read the whole line, its end points and the opponent's threats before deciding that a pattern forces a win.
Open three
Three stones with room on both sides can become an open four. Deal with this threat before it develops, unless you have a stronger forcing move.
Broken three
Three stones with an internal gap. Filling the marked gap makes four; check that both ends allow a valid winning continuation.
Blocked three
One end is blocked. Usually less urgent than an open three, but it can join another threat. Do not dismiss it automatically.
Four
One more stone completes five. Block the winning point unless you can win immediately yourself.
Open four
Four consecutive stones with two winning extensions. Usually decisive: the opponent cannot block both with one stone, provided both extensions are legal and they cannot win first.
Four–three (4–3)
The marked move creates a four and an open three. If the opponent must block the four, you may turn the three into an open four. Read counter-threats and blocked ends.
VCF: continuous fours
A forcing winning sequence built from repeated four-threats. Each defence must be checked until a valid, unavoidable win is reached.
VCT: continuous threats
A broader search combining three- and four-threats. It requires deeper reading of legal defences and counterattacks.
Caro can invalidate an apparent winning point if the completed five is blocked at both ends. Renju adds forbidden-move checks for Black. A pattern name alone is not proof of a forced win.
Beginner tips and common mistakes
Check immediate wins first
Look for your own winning move, then the opponent's. A real four-threat usually needs an immediate answer.
Leave room around your stones
Central stones have more space to extend. Near an edge, count whether five can still fit.
Scan all four axes
Inspect horizontal, vertical and both diagonal lines through the last move. Diagonals are easy to overlook.
Use forcing moves carefully
Fours can gain the initiative, but a row that cannot legally win does not force a defence.
Look for intersecting threats
One move may strengthen two lines. Read both continuations and check forbidden moves if playing Renju.
Count the endpoints
In Caro, a corridor of exactly five spaces between two blocks cannot produce a winning row along that axis.
Mistake: Attacking without checking the last move.
Instead: Scan the opponent's new threats before choosing your plan.
Mistake: Treating every three as equally urgent.
Instead: Compare legal extensions, open ends and combined threats.
Mistake: Missing a diagonal.
Instead: Trace both diagonals through each newly placed stone.
Mistake: Blocking the wrong end of a broken four.
Instead: In X X · X X, the winning point is the internal gap.
Mistake: Starting without agreeing on the rules.
Instead: Confirm overlines, blocked ends, edges and any opening restrictions.
Useful terms
- Gomoku
- The international Japanese-derived name for five-in-a-row.
- Blocked ends
- An opposing stone or fixed edge immediately beyond an uninterrupted row.
- Overline
- An uninterrupted row of six or more stones.
- Open three
- A three that can develop into a legal open four.
- Four
- Four stones with a move that completes a valid five.
- Open four
- A straight four with two valid winning extensions.
- 4–3, 3–3, 4–4
- Two threats created by a single move.
- VCF
- Victory by continuous four-threats.
- VCT
- Victory by continuous threats, including threes and fours.
- Forbidden move
- A Black move restricted by Renju's pattern rules and their exceptions.
- Swap2
- An opening procedure with a colour choice and an optional two-stone extension.
- RIF
- Renju International Federation; publisher of Renju and Gomoku tournament rules.
The rules in one minute
- Two players; Black (X) starts on an empty 15 × 15 board.
- Place one stone per turn on an empty point. Stones do not move or capture.
- Count consecutive stones horizontally, vertically or diagonally.
- Caro: exactly five, with at least one unblocked end. Edges block.
- Standard: exactly five; blocked ends do not matter.
- Freestyle: five or more; blocked ends do not matter.
- A valid line ends the game immediately. A full board without a winner is drawn.
- Renju and Swap2 are tournament conventions, not rules automatically applied in these three modes.
Frequently asked questions
Are Caro and Gomoku the same?
They share the five-in-a-row idea. Vietnamese Caro often adds blocked-end rules. Always agree on the exact variant.
How many stones win?
Exactly five in Caro and Standard; five or more in Freestyle. Caro also requires at least one unblocked end.
Does the board edge block a line?
Yes, in ChessPlayX Caro. An edge on one side and an opposing stone immediately on the other block both ends.
Does six in a row win?
In Freestyle, yes. In Caro and Standard, that row does not win. An exact five on another axis can still win on the same move.
Does the first player have an advantage?
Yes. Tournament rules such as Renju and Swap2 are designed to reduce the opening advantage.
How big is the board?
Regular ChessPlayX Caro uses 15 × 15 points. The 11 × 11 board in this article is a smaller teaching board.
Can I pass or remove a stone?
No in these three ChessPlayX modes. Each turn places one stone. The article's Undo button is a practice tool, not a capture or pass.
Does ChessPlayX apply Renju forbidden moves?
No. Caro, Standard and Freestyle use their own winning-line conditions. The Renju section explains a separate tournament ruleset.
What is Swap2?
A places Black, White, Black. B chooses a colour or adds White then Black and lets A choose. The player assigned White moves next.
Where should I play first?
Near the centre is a useful starting point because there is room in every direction. It is not compulsory in these three regular modes.
What should you learn next?
- Compare the three winning rulesReturn to the practice board and try each preset.
- Solve Caro puzzlesPractise recognising threats in the puzzle catalogue.
- Play against AIChoose a computer opponent for your next game.
- Start a Caro gameChoose your rules and preferred way to play.
- Learn GoAnother intersection game, with territory and captures as its focus.
Rules and references
- Renju International Federation — International Rules of Gomoku
- Renju International Federation — International Rules of Renju
This guide's Caro examples match ChessPlayX: a 15 × 15 board, Black first, exactly five and no win with both ends blocked; edges count as blocks. Standard and Freestyle are also available. Renju, Pro and Swap2 are explained for comparison. The linked RIF documents describe tournament rules; their opening, claim and clock procedures differ from these regular online modes.