What Makes a Good Logic Puzzle? The Five Tests We Use

Before a puzzle goes into the notebook it has to pass five plain tests. Here they are, with the puzzles that taught us each one.

There are thousands of HTML5 games on the web and most of them are forgotten ten minutes after you close the tab. A handful stay with you. When we were choosing the twenty puzzles for GridPencil, we kept coming back to the same five questions, and a puzzle that failed even one of them did not get in.

1. Can the rules be said in four lines?

Every puzzle page here has a rules box with exactly four lines in it. That is not a design accident. If a puzzle needs a fifth line, it usually means there is an exception hiding somewhere, and exceptions are where people get frustrated.

River Crossing is the model. A boat, three passengers, two pairs that cannot be left alone. You understand it before you have finished reading it, and you can still get it wrong.

2. Is there a definite answer?

A logic puzzle should end with a click, not a shrug. Either all ten nonogram lines match or they do not. Either the eight queens are at peace or two of them are glowing red.

This rules out a lot of otherwise pleasant games. Anything where you simply play until you lose is a pastime, and there is nothing wrong with that, but it is not what this site is for. The nearest we get is Block Collapse, and even there we set a finish line: four blocks or fewer left on the board.

3. Can you reason your way there?

This is the big one. In a good puzzle, every move can be justified. You place a digit because nothing else fits, not because it feels lucky.

It is also the hardest test to pass with puzzles that are generated at random, because a random board may have two answers, or none. So the generated puzzles here are checked before you ever see them. Sudoku Six and Binary Grid always have exactly one solution. Water Sort is tested to make sure it can be finished.

We made one honest exception. Mine Sweep will occasionally leave you with a real coin toss, because that is what the game is and always has been. We decided it would be stranger to leave it out.

4. Does it respect five minutes?

Most of the puzzles in the notebook take between two and eight minutes. That was deliberate. A puzzle that needs forty minutes is a commitment, and people put commitments off. One that needs five gets played while the kettle boils.

Short does not have to mean easy. Peg Solitaire is thirty-one jumps and you can fail it in all sorts of interesting ways for weeks.

5. Is it still good the second time?

Some riddles are wonderful exactly once. After you know the trick, there is nothing left. We kept a few of those because they are too famous to skip, but most of the list is made of puzzles that come back fresh: a new sudoku, a new sheet of ice, a new knot to untangle.

The best ones do something more. They teach you a method, and the method is the fun part. Once you see how Two Jugs really works, every new pair of jugs is a small chance to show off.

What we left out

A few things failed on purpose:

• Anything with a countdown clock bolted on to make it "exciting".
• Anything that needs fast fingers more than a clear head.
• Anything where the difficulty comes from hiding the rules.
• Puzzles that need a big screen to be readable at all.

That last point matters more than it sounds. HTML5 games run on whatever you happen to be holding, so a puzzle has to work on a phone held in one hand and still look right on a wide monitor.

Use the tests yourself

Next time a puzzle annoys you, run it past the five questions. Usually you will find it broke the third one: at some point it asked you to guess and called it thinking. And if you know a puzzle that passes all five and is not in the list, we would like to hear about it. The address is on the contact page.