How Codex Numbers works
Codex Numbers is played by guessing a hidden number: each attempt comes back with how many of your digits are correct and how many sit in the right position, and you use those two counts to rule numbers out until your guess is the hidden one. There is no opponent and no multiplayer — just the number, your attempts and what their answers add up to.
Codex Numbers works as a single loop: you guess a hidden number, and the game answers with two counts — how many of your digits are correct, and how many of them sit in the right position. You read those counts, build the next guess out of them, and keep going until the guess you enter is the hidden number itself. The tagline on its game page puts the idea in two short sentences: guess the hidden number, and every attempt narrows it down. Codex Numbers is a free puzzle game, rebuilt in Unity from the original Mastermind Numbers and published on both the App Store and Google Play. What follows is how a round runs and how to read the two counts so that every attempt earns its place.
What you are trying to find
When a round starts, there is a number in play that you cannot see. You never get to look at it directly; everything you learn about it arrives through the answers to your own guesses. That is what makes Codex Numbers a deduction game rather than a game of chance. The answers are not vague hints — each one is an exact statement about how your guess compares with the hidden number, and it stays true for the rest of the round. The game is listed under Puzzle · Logic, and it has no multiplayer: nobody is sitting opposite you, so the round is between you and the number.
One turn, step by step
- Look back first. Every answer you have already received still limits what the hidden number can be, not only the latest one.
- Enter a guess. Choose it for what its answer can teach you, not only for its chance of being right.
- Read the first count: how many of your digits are correct. This is about which digits the hidden number is made of.
- Read the second count: how many sit in the right position. This is about whether the digits you got right are standing where they belong.
- Note what the pair of counts rules out, and build the next guess from those notes.
- Repeat until every digit you enter is both correct and in its place — at that point your guess is the hidden number.
Two counts, two different questions
The most common beginner's mistake is to treat the answer as a single score: a higher number is good, a lower one is bad. It is really two pieces of information, and they answer different questions. The table below keeps them apart, together with a third number you can work out yourself from the first two.
| What you read | What it tells you | What it leaves open |
|---|---|---|
| Correct digits | Which digits belong to the hidden number — its composition. | Where those digits go. |
| Digits in the right position | How many of the correct digits are already in their place — the arrangement. | Which ones those are. |
| The gap between the two | How many digits belong to the number but stand in the wrong place. | Which places they should move to. |
What the common answers mean
A few kinds of answer come up again and again, and recognising them saves attempts. If nothing comes back as correct, none of the digits you entered is in the hidden number, and all of them can be struck from your notes at once — a strong result, not a wasted attempt. If several digits are correct but none is in position, you know which digits to keep, and also one place each of them cannot go. If some digits are correct and some of those are in position, the guess mixes digits that are already home with digits that still have to move; change only one thing next, so the answer can tell you which is which. And once every digit is correct, composition is solved: no further guess needs to test a new digit, and every remaining attempt goes on order.
Reading two guesses side by side
Answers say far more when you compare guesses than when you read each one alone. Take two attempts that are identical except for a single digit you swapped out for another. If the correct-digit count went up by one, the newcomer belongs in the hidden number; if it went down by one, the digit you removed was the one that belonged. If it stayed the same, either both digits belong or neither does, and one more guess can settle which. Arrangement works the same way. Keep the digits and only exchange the places of two of them: the correct-digit count cannot move, because the same digits are still in the guess, so whatever happens to the in-position count was caused by that exchange alone. A rise means at least one of the two landed where it belongs; a fall means at least one of them was already in its place and you have just moved it away. Changing one thing per attempt is what makes every answer traceable to a cause.
Habits worth building
- Spend the early attempts on coverage. A guess that rules several digits out has done more work than a near miss.
- Settle which digits belong before working on their order. Arranging a known set is a much smaller problem than solving both at once.
- Check each guess against every earlier answer. One that could not be the hidden number only brings information — fair early in a round, rarely worth it late.
- Use a digit you know is absent as a blank. It adds nothing to either count, so the answer speaks only about the other digits.
- Skip any guess whose answer your notes already predict. It teaches you nothing.
These are the same habits our Bulls & Cows guides describe, and they carry over because the answer in Codex Numbers has the same two parts. The longer guide on choosing each next guess is at /blog/narrowing-the-hidden-number-faster/
What this guide leaves to the game
The Codex Numbers game page describes the loop — a hidden number, a guess, and an answer in two counts — and this guide stays within it. How many digits the hidden number has, and what the screen shows around your guesses, are things you will see in the game itself during your first round. Nothing above depends on them: changing one digit at a time, treating a zero as a result and solving composition before arrangement work the same way whatever the length of the number.
Where Codex Numbers comes from
Codex Numbers was rebuilt in Unity from the original Mastermind Numbers, it comes with Google Play Games support, and its release date is 2 April 2017. If you played Mastermind Numbers, Codex Numbers is the game rebuilt from it; the MagicLampGames catalogue has no separate entry under the older name. The same guess-and-answer loop also runs in Bulls & Cows, an iOS-only MagicLampGames title with modes of its own, and the two games are compared at /blog/bulls-and-cows-vs-mastermind/
Getting the game
Codex Numbers is free on both the App Store and Google Play, with version 1.7.14 live on each. Its Google Play listing is currently restricted by country: it opens from Turkey, but the store link may not open from every other region. The game is available in thirteen languages — Turkish, English, German, French, Spanish, Italian, Dutch, Danish, Russian, Japanese, Korean, Chinese and Arabic. The game page, with screenshots and links to both stores, is at /games/codex-numbers/