Number Detective

Enter a guess and read the reply: a 'locked' peg means a correct digit in the correct spot, and a 'loose' peg means a correct digit in the wrong spot. Unlock property clues, facts about the secret like parity, divisibility or digit sums, to narrow the field without spending a guess. Identify the exact number before you exhaust your limited guesses.

• Locked = right digit, right position; loose = right digit, wrong position.
• Reveal a property clue any time, it costs a little score but no guess.
• You have a limited number of guesses per case.
• Cross-reference clues with peg feedback to corner the answer.

• Daily: the same case for everyone, in 3-digit, 4-digit, or 4-distinct-digit modes.
• Practice: fresh random cases at your chosen difficulty.

• Desktop: type digits and press Enter to submit; use 'Reveal clue' for a new tell.
• Phone & tablet: tap the on-screen number pad to enter digits, ⌫ to delete, Guess to submit.

• Spend an early clue or two, a divisibility fact often eliminates more numbers than a guess.
• Track which digits are confirmed present but misplaced, then test new positions for them.
• Solve quickly with few clues; both time and clue use lower your score.

Number Detective sharpens mental math and number sense by combining guess-and-feedback deduction with real clues about a hidden number's properties.

• Skills: number properties (primes, factors, parity), logical deduction, mental arithmetic
• Best for: roughly grades 5–8 (ages 10–14)
• For parents & teachers: blends logic and number theory into a satisfying daily puzzle.

Locked and loose pegs — a correct digit in the correct place, or in the wrong one — is the feedback scheme of Mastermind, invented by Mordecai Meirowitz in 1970, and of its pencil ancestor Bulls and Cows.

Unlocking property clues about the hidden number as you go is the original addition.

Those clues change the search from positional to mathematical. Knowing a digit is in the right place narrows the arrangement; knowing the number is divisible by three constrains the digits themselves — two different kinds of information about the same secret.

Number Detective is an original, free browser deduction game that fuses positional guess feedback with genuine number-theory clues to sharpen mental math. Play instantly, no install.

A free, original browser game on PlayPendium. No download, no install.