LABS TIC-TAC-TOE • 12 Opponents

12 opponents A ladder of blunder rates — every card shows its own.

3 ways to play The computer, two chairs at this screen, or a friend on a link.

1 cannot lose LETHAL plays perfectly, 0% blunders — against him a draw is the win.

Choose an opponent, then New game

You — X

0:00

Computer — O

0:00

Controls

Game

Engine

Clock

Board

Choose opponent

The engine

Minimax with alpha-beta pruning, full width, depth-limited per opponent
Win scores are depth-adjusted, so it takes the fastest win available and the longest loss — it will not dawdle over a mate it already has, or walk into one a move early
A small centre bonus breaks ties between otherwise equal moves

Tic-tac-toe is a solved game. A perfect player can never lose, so a ladder built only on search depth is a ladder where every rung plays the same. The twelve differ by a blunder rate: the chance of playing a random legal move instead of the best one
Every card shows its own rate. LETHAL is 0% and cannot be beaten — against it a draw is the win
Search depth still varies (4 to 6) and still matters in the opening, where a shallow search can miss a fork one ply past its horizon

Three rules and nine cells: the grid is the gap between the cells, not a border on every third one
X and O are stroked SVG, so they hold their shape and weight at any size and draw themselves on
The winning three are marked on the board and struck through in the winner's own colour

Live match — two devices over the wire, invite by link or code, visitor links for spectators, the clock carried with the game

Its own address at labs.llc/tictactoe/ — paper is the front door, the dark room is indexdark.html, the old URLs forward
Pass & play — two people, one screen, X and O taking turns holding it
Time controls sized for a nine-cell game: ∞, 10s, 30s, 1m per side, with the flag falling for whoever runs dry

The nine visual themes are gone, and with them the runtime colour injection they needed — one palette, plain CSS, both editions
Undo used to call lastIndexOf on the board array, which finds the highest index holding a mark and not the last move played. There is a real move history now
The board was a checkerboard at 1.19:1; the marks were text with a five-layer glow; the winning line was never shown; the board could not be played from the keyboard
Preferences persist. Board colours are shared with chess and checkers