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Coding and decoding

If CAT is coded as DBU, what is EPH? One example shows a code — a shift, a reversal, a mirror, letters as numbers. Find it, then code or decode a word.

  • Words
  • Timed
  • 9 levels

How it plays

One word and its coded form are shown. Work out the code from that example, then decode another coded word — or, if you turn it on, code a new word yourself.

Codes unlock as you climb: move every letter along the alphabet, write the word backwards, write letters as their places (A = 1), backwards and shifted, the mirror alphabet (A↔Z), one more step at each letter, steps that take turns, swapped pairs. The words get longer as you go, and there is a top: every code on the longest words is the last level.

Every code the game knows is tried on the example, with every shift; the question is only asked when every code that fits gives the same answer. The wrong options come from codes that almost fit the example.

Keys

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

What it trains

This practises finding a letter rule from one example and applying it exactly — the coding-decoding questions of aptitude tests. It claims nothing wider.

Learn

How to get better at coding and decoding: 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. Line up the example word and its code, letter under letter, and write each letter’s place (A 1 … Z 26).
  2. If the code is numbers, it is places — check whether A is 1, or 1 plus some number.
  3. Compare the first code letter with both the first and the last plain letter. If it sits near the last, the word was written backwards first.
  4. Find the step at every position. The same step is a shift; a step growing by one is a stair; on-then-back is alternating; places adding to 27 is the mirror; the same letters with pairs swapped is a swap.
  5. Apply the rule to the other word — forwards to code it, every step undone to decode it — and check the result on one letter of the example.

Techniques and tricks

  • EJOTY landmarks

    E is 5, J 10, O 15, T 20, Y 25. Step from the nearest landmark instead of counting from A.

    e.g. FORK → GPSL: F 6 → G 7, a step of 1. So COD → DPE.

  • Wrap round at 26

    Past Z the alphabet starts again at A, and before A comes Z. Add or take 26 to land back inside 1 to 26.

    e.g. CANADA → DZOZEZ: one on, one back in turn, and A one back is Z.

  • Mirror letters add to 27

    In the mirror code A↔Z, B↔Y, C↔X: each pair of places adds to 27. Take the place from 27.

    e.g. CAT: C 3 → 24 X, A 1 → 26 Z, T 20 → 7 G. So XZG.

  • Backwards, then shifted

    Write the word backwards first, then apply the step. When decoding, undo the step, then read backwards.

    e.g. FIG backwards is GIF; one on is HJG.

  • The growing stair

    If the step is one more at each letter, find the first step and count up from it.

    e.g. SANDAL → VESJHT: steps 3, 4, 5, 6, 7, 8. So SWAMP → VAFSW.

  • Number codes: take off the start

    When the numbers run high, find what A would be, subtract the extra, and read places.

    e.g. A = 6 code: 17 6 12 20 20 19 → 12, 1, 7, 15, 15, 14 → LAGOON.

  • Swapped pairs

    Swap the 1st and 2nd letters, the 3rd and 4th, and so on. With an odd number of letters, the last one stays put.

    e.g. TOWER → OTEWR.

As the levels climb

  • You start with a shift of a step or two, and writing backwards, on three- and four-letter words. Early shifts mostly stay inside A to Z.
  • Then letters as their places (A = 1) and backwards-with-a-shift; four- to five-letter words; 80% of the time. Shifts get wider as codes open, up to 12 either way.
  • Then the mirror, the stair and alternating steps; five- to six-letter words; 65% time; then swapped pairs and places-plus-a-number; then six- to seven-letter words. That is the top.
  • Each harder code and each longer word adds time. Longer words leave more letters to slip on, so check two letters of the example, not one.

Traps to avoid

  • A code that almost fits. The wrong options come from codes that get one letter of the example wrong — often a shift one too big or too small. Check the step on two letters.
  • Lookalike words. When decoding, real words of the same length sharing letters in place with the answer are offered. Decode every letter, not just the first few.
  • The word left plain. When coding, the word itself, uncoded, is offered. A code always changes it.
  • Undoing the wrong way. If the code moves letters 3 on, decoding moves them 3 back. Going on again doubles the shift.

How to practise

  • Use “Questions” to practise “Decode a word” or “Code a word” alone; coding asks you to produce every letter, decoding to undo it.
  • Switch “Answer by” to “Typing the answer”. For number codes, type the numbers with spaces between them.
  • Lower “Options shown” to 2 while a code is new; raise it towards 8 for more near codes to rule out.
  • Learn the mirror pairs by heart — A–Z, B–Y, C–X, D–W, E–V … M–N — so the mirror code needs no sums.

Levels

Each question has a clock that comes from the work it asks for. There are 9 levels with the default settings, and the counter stops at the real top. 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.

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