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Codebreaker

Deduce a hidden code from ● and ○ clues. Each turn, pick the guess that fits every clue so far. Longer codes and more letters, without end.

  • Logic
  • Untimed
  • Endless levels

How it plays

A secret code of letters is hidden. Each guess scores ● for every letter in its right place and ○ for every right letter in the wrong place. All guesses and their scores stay on screen.

Each turn offers a few guesses, and at least one fits every clue so far — it could still be the secret. Find it: check each offer against every clue. Par is what a player who always picks a fitting guess needed, plus a little slack. Levels add letters to choose from, then lengthen the code without end.

Keys

Space starts and skips ahead · 1–9 pick · Enter submits · Esc stops. On a phone, tap.

What it trains

This practises checking a hypothesis against every piece of evidence, not just the latest. It is practice at this puzzle and claims nothing wider.

Learn

How to get better at codebreaker: the method, the techniques, what each new level asks of you, and the traps the wrong answers are made of.

Your approach to each question

  1. On the first turn every offer fits, because there are no clues yet. Pick any one and look at what it scores.
  2. From then on, take one offer and pretend it is the secret. Score each earlier guess against it: how many ● it would get, and how many ○.
  3. If any clue comes out different — even by one peg — drop the offer and move to the next. If every clue matches, it fits, and you can play it.
  4. Any fitting offer is a good move. From the fifth guess on only the secret fits, so a player who always picks a fit never needs more than five — spend your effort on checking, not on choosing between fits.

Techniques and tricks

  • Count the shared letters first

    ● plus ○ is the number of letters the two codes share, counting repeats. Count that for the offer against a clue before you look at positions; it rules most bad offers out in one glance.

    e.g. Clue ABC ●○: shared letters must be 2. BAD shares A and B, which is 2 — so go on to positions

  • Then count the places

    Line the offer up under the earlier guess and count the columns where the letters match. That count must equal the ●s exactly.

    e.g. Clue ABC ●○. BAD matches in no column, so it would score ○○, not ●○ — out. ACD matches in the first column and shares C elsewhere: ●○, it fits

  • The empty clue

    A guess that scored nothing shares no letter with the secret. Every letter in it is gone from every position — strike any offer that contains one.

    e.g. ABB scored nothing: any offer with an A or a B is out

  • Repeats count once each

    A letter scores as many times as it appears in both codes, no more. Two As in the guess against one A in the secret score one peg, not two.

    e.g. Clue AAB ●. ACC shares one A, in place: ●, it fits. CAA shares two As, one in place: ●○, out

  • Check the strictest clue first

    Test each offer against the clue with the most pegs, or against an empty clue, before the others. Those rule out the most codes, so a bad offer usually fails on the first check.

  • All pegs, no places

    A clue of only ○s, as many as the code is long, means the guess holds every letter of the secret but none in its place. Each fitting offer is a rearrangement of it with no letter where it was.

    e.g. ABC scored ○○○: the secret is BCA or CAB

As the levels climb

  • The ladder starts with codes of 3 letters from A to C. It then lengthens the code and widens the alphabet in turn: 4 letters from 3, 4 from 4, 5 from 4, 5 from 5, and so on.
  • At 8 letters, A to H, the alphabet stops growing and only the code gets longer, without end. Long codes mean more columns to line up, so count places slowly and point at each column.
  • As the code grows, each clue carries more pegs, and a wrong offer can match the shared-letter count by chance. Expect to need the place count more often on long codes.
  • However long the code, from the fifth guess on (the fourth, on 3-letter codes) the secret is the only offer that fits. So the hard checking is in your second to fourth guesses, and it gets harder as the code grows.

Traps to avoid

  • Checking only the last clue. The wrong offers are the codes that break the fewest clues — often just one, and it need not be the newest. Check every line on the board.
  • Reading ○ as “wrong”. ○ means a right letter in the wrong place, so that letter is still in the secret. An offer that drops it altogether breaks the clue.
  • Counting a repeated letter twice. If the earlier guess has one E and the offer has two, they share one E. Count each letter by the smaller of its two counts.
  • Keeping a letter in its old place after a clue scored no ●. If a guess scored only ○s, none of its letters sits where it stood — an offer that keeps any of them in place is out.

How to practise

  • Lower “Guesses offered” to 3 while you learn the two counts; raise it toward 9 later, when picking out the one fit among many is the skill.
  • Raise “Extra guesses allowed” to 5 while you learn, so one slip still finishes. Lower it a step at a time; at 0, even a fitting pick that happens to take one guess longer than the worked path costs the trial.
  • Say both numbers for every clue before you decide: “shares two, one in place”. Saying it out loud stops you skipping clues.
  • After each game, read the line in the working that shows a consistent path. Compare it with yours to find the guess where you played an offer that did not fit.

Levels

It is untimed unless you turn the clock on. There is no last level: at least one dial turns without end. Your level is judged on your last ten answers, every ten: 90% moves you up, below 80% moves you down, which holds most people near four in five right.

All of it is in the settings beside Start — how many answers a judgement looks at and how often it recalibrates, the thresholds, the time, which questions, how many options, and whether you see each verdict at once or review them together at the judgement. You can also jump to any level.

More logic

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