Codex

Three daily word puzzles. Crack each word using Mastermind-style clues — count only, no letters revealed.

About Codex

Codex is a daily word puzzle based on the classic code-breaking game Bulls and Cows, the pencil-and-paper ancestor of Mastermind. Every day there are three secret words: an easy 4-letter word, a medium 5-letter word and a hard 6-letter word.

The twist compared with Wordle is that Codex never tells you which letters are right. Each guess only gives you two numbers: how many letters are in the correct position, and how many are in the word but in the wrong position. Working out which letters those are is the puzzle.

There's no limit on guesses. Your score for each word is how many guesses it took, and the daily leaderboard ranks everyone who played the same three words that day.

How to play

Pick a puzzle: Easy (4 letters), Medium (5 letters) or Hard (6 letters). You can do them in any order and switch between them.
Type a word of the right length and send it as a guess.
Read the two counts. The green count (bulls) is how many letters are in exactly the right place. The amber count (cows) is how many letters are in the word but somewhere else.
Use the counts from all your guesses together to rule letters in and out, then guess again.
When every letter is a bull, you've cracked it. Solve all three to finish the day. If you're truly stuck you can give up on a word and see the answer.

Example: the 4-letter word is BEAR

BARN: 1 bull, 2 cows. B is in the right place, and A and R are in the word but in the wrong spots. N isn't in the word.
BEAD: 3 bulls, 0 cows. B, E and A are all in the right places, so only the last letter is wrong.
BEAR: 4 bulls. Solved in three guesses.

Tips

Make your first guesses with as many different common letters as possible. A guess with zero bulls and zero cows is just as useful: it rules out every letter in it.
Change one or two letters at a time once you're close. If the counts go up or down, you know exactly which letter caused it.
Keep track of letters you've ruled out. A quick mental list of "definitely not in it" letters saves a lot of wasted guesses.
Start with Easy. The 4-letter word is the quickest way to warm up before the 6-letter one.

FAQ

What are bulls and cows?

They're the traditional names from the original code-breaking game. A bull is a correct letter in the correct position. A cow is a correct letter in the wrong position.

How is Codex different from Wordle?

Wordle colours each letter, so you know exactly which ones are right. Codex only gives totals, so you have to deduce which letters the counts refer to. There's also no six-guess limit.

Can I play Codex with friends?

Codex is a solo daily puzzle, so everyone gets the same three words and compares scores on the leaderboard. For playing together in a room, try Warmer or Spectrum.

When do the words change?

Every day at midnight UTC there are three new words for everyone.

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