Four-digit deduction
Solve four digits together with A/B clues in ten guesses.
How to use
Share one device with 2–6 people to solve a four-digit code. The answer uses four different ASCII digits and may start with 0. Follow A/B clues with up to ten valid, distinct guesses. No timer or login.
Start in three steps
- Discuss and enter four different ASCII digits from 0–9. A leading 0 is allowed, for example 0123.
- Check A/B after submitting: A means the right digit in the right position; B means the right digit in a different position. Invalid or repeated guesses do not use an attempt.
- Reach 4A0B within ten guesses to win, including on the tenth attempt. Ten misses end the round. Both outcomes reveal the answer and lock input. Restarting requires confirmation.
Storage and limitations
The answer, input, guesses and clues stay in page memory only. They are not sent to a server or saved to persistent storage. Leaving, refreshing or page eviction clears them. There is no timer, individual score or cross-device connection. Developer tools can inspect the local answer; this is not a competition anti-cheating tool.
Frequently asked questions
What do A and B mean in four-digit deduction?
A counts digits in the correct position. B counts digits present in the answer but in a different position. No digit counts as both A and B. For answer 0123, guess 0132 gives 2A2B.
Can a code start with 0? Do invalid guesses use an attempt?
Yes. Answers and guesses preserve all four characters, including a leading 0. Wrong length, non-ASCII digits, repeated digits or a combination already guessed this round show an explanation and use no attempt.
Does a correct tenth guess win? Can I resume after refreshing?
A correct tenth guess still wins. You lose only if all ten accepted guesses miss. The round stays in page memory only and cannot be resumed after refreshing. Restarting requires confirmation; cancel keeps the current round.