Code – a colour code logic puzzle

How it works

The puzzle is based on the classic code-breaking principle: clues made of black and white pins. It is played differently, though. The rows at the top of the board are not your guesses — they are part of the task and have already been scored. You enter exactly one code: the one that fits every row.

• A black pin means one colour is right and in the right place. Which one, it does not say.
• A white pin means one colour is in the code, but in a different place from where it sits here.
• No pin: for every peg that comes away empty-handed, the code has no counterpart left.

The order of the pins means nothing. They are a count, not a pointing finger — and that is exactly where the thinking comes from. Every colour also has a shape: circle, square, triangle, diamond, star, hexagon. If colours are hard for you to tell apart, read the shapes; both say the same thing.

Tap a colour below to fill the next empty slot, and tap a filled slot to clear it again. Once all four slots are filled, your answer is checked. On this page you play in practice mode: Code is already selected, so you choose Easy, Medium or Hard and begin. As often as you like, nothing is scored, and the clock simply counts upwards. Code deduction also appears in the Daily Sprint, in Endless, in Deduction Rush and in duels.

Tips & techniques

• Think in possible codes, not in single slots. On Easy there are only 24 possible codes to begin with: four slots, four colours, none used twice. Every scored row cuts some of them away.
• Elimination. The normal case: a row fits some codes and not others. Any code that would have earned this row a different score is out. What you test is the score, not how similar things look.
• Start with the row that has the fewest pins. It says the most about what the code is not, and ruling out is cheaper here than confirming.
• White pins alone are a strong clue. A row with four white pins and no black one says: all four pegs are in the code, but none of them sits where it sits here. That forbids one colour for every slot.
• Pins count pegs, not colours. If a colour appears twice in the guess and once in the code, that earns one pin, not two. The scored guesses almost always repeat a colour — so anyone counting colours instead of pegs gets nearly every board wrong.
• Only one left. If exactly one code remains after all the rows, it is the one you are looking for. The final step is not a hunch but a count. Before you enter your candidate, test it against every row once more.

Frequently asked questions

Do I have to guess the code?

No. Unlike the classic game, you get no guesses of your own, and you do not need them: exactly one code fits all the scored rows. You find it by ruling out the others.

Can a colour appear twice in the code?

Not on Easy or Medium. On Hard it can — there the code always repeats a colour. The scored guesses may contain repeats at every level; the rule restricts the code, not the questions put to it.

How else do the difficulty levels differ?

The code always has four slots. Easy uses four colours and three scored rows, Medium five colours and three or four rows, Hard six colours and three or four rows. With each level more codes stay possible for longer, and you have to keep more of them in view.

Why is there no hint button here?

In the grid puzzles a hint shows the next cell that can be deduced. Here there often is no such cell: the solution emerges from all the rows together, not slot by slot. That is why Code deduction has no hints in practice mode. A wrong entry costs nothing there, though — you can simply try again.

Does it cost anything?

No. The puzzle runs free of charge in your browser, and you do not need an account.