Sunday 4 October
Free HTML5 Games for People Who Like to Think
GridPencil is a notebook of twenty logic puzzles. Each one opens in your browser, explains itself in four lines, and makes a new puzzle every time you ask.
Today's puzzle, No. 11
Eight Queens
Place eight chess queens on the board so that no queen can capture another.
Logicabout 5 min
Start today's puzzleContents
- 01Mine SweepOpen every safe square on a 9 by 9 field without touching one of the ten hidden mines.
- 02Sudoku SixA smaller sudoku: fill a 6 by 6 grid so each row, column and box holds the digits 1 to 6.
- 03Nonogram 5×5Shade squares to match the number clues on each row and column and reveal a small pattern.
- 04Code BreakerFind the hidden four-digit code in ten guesses, using the feedback after each attempt.
- 05Tower of HanoiMove a stack of discs from the left peg to the right, one at a time, never placing a larger disc on a smaller one.
- 06Peg SolitaireJump pegs over each other on a cross-shaped board until only one remains.
- 07Pipe TwistRotate the pipe pieces until every square is connected to the red source in the middle.
- 08Colour FloodSpread one colour across the whole board in 22 moves or fewer, starting from the top left corner.
- 09Water SortPour coloured layers between tubes until each tube holds a single colour.
- 10Knight's TourMove a chess knight around a 5 by 5 board so that it lands on every square exactly once.
- 11Eight QueensPlace eight chess queens on the board so that no queen can capture another.
- 12Block CollapseClear groups of matching blocks. Bigger groups score far more, so plan before you tap.
- 13Magic SquareArrange the numbers 1 to 9 in a 3 by 3 grid so that every row, column and diagonal adds up to 15.
- 14UntangleDrag the dots so that none of the lines between them cross.
- 15Ice SlideSlide across the ice to the flag. Once you start moving, you only stop when you hit something.
- 16Two JugsMeasure out an exact amount of water using only two unmarked jugs of different sizes.
- 17Schulte GridFind and tap the numbers 1 to 25 in order, as fast as you can.
- 18Pattern RecallA pattern of squares lights up for a moment. When it disappears, tap the same squares from memory.
- 19River CrossingFerry a wolf, a goat and a cabbage across a river in a boat that carries only one of them at a time.
- 20Binary GridFill the grid with 0s and 1s so that no three alike sit together and every line is balanced.
What you will find in this notebook
GridPencil collects twenty puzzles of the kind that used to fill the back pages of newspapers and the margins of maths books. Some are centuries old, like the river crossing riddle and the magic square. Others, like sudoku and the nonogram, are modern classics. All of them are HTML5 games, which means they run inside the page you are reading, on a phone, a tablet or a computer, with no app and no download.
Made to be solved, not just played
Every puzzle here has a definite answer, and wherever a puzzle is generated at random the site checks that it can be solved before showing it to you. Sudoku and Binary Grid always have exactly one solution. Ice Slide tells you the shortest route that exists. Nothing depends on quick reflexes, and nothing is timed unless measuring your time is the whole point.
Your progress stays with you
When you solve a puzzle, a tick appears beside it in the contents list. Those ticks are stored in your own browser, not on our server, so there is no account to create. Each puzzle page has the rules in four lines beside the board and a longer guide underneath, with the reasoning that experienced solvers use.
Where to begin
If you are new to logic puzzles, start with River Crossing, Pipe Twist or the small Nonogram. For something meatier, try Binary Grid or Peg Solitaire. Or simply take today's puzzle at the top of the page. It changes every day and works through the whole notebook in turn.