Guess budget
You get a set number of guesses, and no more.
Spending one on a number you could have ruled out is the whole game.Number deduction, sabotaged
Find the number.
The rules fight back.
High or low gets you started. Then mines occupy the clever moves, your own guesses disappear, the keypad scrambles and the board starts lying about what you pressed.
- 32 included challenges
- 11 combinable mechanics
- £2.99 optional permanent Designer
The familiar part
One hidden number. Higher. Lower. Correct.
Every round tells you a range. Enter a guess, read the verdict and narrow the possibilities. The catch is that each challenge removes one of the assumptions that makes ordinary binary search easy.
- 1Read the challenge
See the range, guess budget and named mechanics before you commit.
- 2Make a legal guess
Some boards ban the middle or limit how far your next guess may move.
- 3Question the verdict
A mine tells you nothing. A lie changes the number recorded in your history.
- 4Find the target in budget
Wrong turns are the currency. Spend them before the rules spend them for you.
Nothing hidden from the player
Know the rule. Discover the consequences.
The game names every mechanic and explains what it costs. It does not reveal mine positions, forbidden numbers after their brief showing, reward positions or which history entries are lies.
Open Rules from the first screen at any time. When a mechanic first affects a round, the app teaches it at the first safe moment—after a lie is no longer able to spoil itself.
The complete rulebook
Eleven ways to break the obvious strategy
Each mechanic changes a precise rule. Challenges combine them; none is merely a difficulty label.
Guess clock
Each guess has its own time limit. The clock restarts after an accepted guess.
Run it down and the round ends—or the keypad scrambles, when that rule is active.Maximum jump
Your next guess must be within a set distance of your last one.
You cannot cross the board in one move. Reaching the far side costs turns.Minimum jump
Your next guess must be at least a set distance from your last one.
The endgame turns awkward when the number you want is too near to be legal.Banned middle
A band through the middle of the live range cannot be guessed.
The perfect split is off the table, so every available split is worse.Mines
Guessing a mined number costs a turn and tells you nothing—not higher, not lower.
They favour the bisection points efficient players naturally choose.Scrambling keypad
Let the clock expire and every digit moves to a new position.
The round survives, but muscle memory does not.Forbidden numbers
A few numbers appear briefly at the start, then disappear. Guess one and pay a penalty.
The cost may burn a turn, cost an extra guess or scramble the keypad.Hidden guesses
Your earlier numbers are masked while their higher/lower verdicts remain.
You must remember which number produced each surviving clue.Lies
Some guesses are recorded as a number you did not press.
The forged entry stays internally consistent; the board commits to its story.Rewards
Some off-line numbers refund a guess, reveal a forbidden number or briefly unmask history.
They reward leaving the safe line; the obvious search never finds them.
Two kinds of play
Fixed when comparison matters. Unstable when chaos is the point.
Train
Same rules, comparable rounds
Train challenges keep their rules fixed. The app records rounds, best results and recent guess counts under that exact rule fingerprint. Change a custom challenge and its old results remain separate.
Play
More variation, no false trend line
Play challenges use mechanics whose hidden arrangement changes the problem. You can replay them as much as you like, but the app does not pretend that two different random boards form a meaningful comparison.
Included at launch
All 32 challenges—and exactly what changes
Everything below comes with the free download. Rule summaries match the bundled challenge documents.
Train · 23 fixed challenges
Masked guesses, five to remember, and six seconds to learn them.
1–200 · 11 guesses · 5 forbidden · hidden guessesYour guesses are masked. Keep the search in your head—a repeat costs a guess.
1–200 · 11 guesses · hidden guessesFind the number. No frills.
1–100 · 7 guessesMasked guesses and a jump limit. A refused move still names your last guess.
1–300 · 14 guesses · 70 max jump · hidden guessesA perfect route has nothing to spare. No slack, no second chances.
1–500 · 15 guesses · 40 max jump · 5 min jumpThree seconds a guess. The keypad shuffles when you hesitate.
1–300 · 13 guesses · 3 seconds · scrambleForbidden numbers and a banned middle push you towards each other.
1–300 · 16 guesses · 5 forbidden · 25% middle bannedEvery guess must move at least 25. The one-step endgame is gone.
1–300 · 21 guesses · 25 min jumpThe middle fifth of whatever remains is off limits.
1–400 · 14 guesses · 20% middle bannedA third of the live range is gone. It costs more guesses than it looks.
1–400 · 17 guesses · 34% middle bannedHalf the live range is banned. Every guess is an edge.
1–400 · 22 guesses · 50% middle bannedA clock and a jump limit. Plan the route while the clock runs.
1–400 · 15 guesses · 6 seconds · 90 max jump · scrambleThree numbers, four seconds. A gentle first forbidden set.
1–120 · 11 guesses · 3 forbidden · 4-second revealFive numbers to remember, then find the answer without touching one.
1–150 · 10 guesses · 5 forbidden · 6-second revealSeven numbers, six seconds. The list is now part of the puzzle.
1–200 · 11 guesses · 7 forbidden · 6-second revealTen numbers, eight seconds. Past here, taking notes is tempting.
1–300 · 11 guesses · 10 forbidden · 8-second revealMasked guesses, a banned middle and eight numbers to remember.
1–400 · 16 guesses · 8 forbidden · hidden guesses · 30% middle bannedEach guess must land within 80 of your last. Bisection stops being freely available.
1–500 · 15 guesses · 80 max jumpThe same walk, with only 50 to work in.
1–500 · 14 guesses · 50 max jumpThirty. Plan the route before you start walking it.
1–500 · 16 guesses · 30 max jumpFive seconds a guess—dawdle and the keypad shuffles.
1–200 · 11 guesses · 5 seconds · scrambleForget a forbidden number and it costs two guesses, not one.
1–200 · 11 guesses · 5 forbidden · extra-cost penaltyOne to ten thousand. A bigger range is a weaker twist than it looks.
1–10,000 · 15 guessesPlay · 9 variable challenges
Nine twists at once. Winnable, which is not the same as sensible.
1–400 · 31 guesses · 9 combined mechanicsThe list of your guesses is not entirely honest. Trust your own memory.
1–200 · 12 guesses · 2 liesTwo entries in your history are lies, and they keep their story straight.
1–300 · 13 guesses · 2 consistent liesSeven forbidden numbers—but some numbers give one back if you find them.
1–250 · 12 guesses · 7 forbidden · 4 reveal rewardsHidden numbers waste a guess and reveal nothing. They favour the obvious middle.
1–200 · 14 guesses · 5 minesHidden rewards refund the guess that finds them. They sit off the obvious line.
1–300 · 10 guesses · 6 refund rewardsForget a number and its cost is drawn for you. Six of them, all different.
1–250 · 12 guesses · 6 forbidden · random penaltiesMines everywhere, with rewards that hand guesses back. Probing can cut both ways.
1–300 · 19 guesses · 8 mines · 5 refund rewardsYour guesses are hidden—but some numbers give them back for a while.
1–200 · 11 guesses · hidden guesses · 4 unmask rewardsChallenge Designer
Every built-in rule becomes your control.
Start blank or duplicate any included challenge. Set the range, budget, clock, jump limits, banned middle, mines, forbidden-number behaviour, hidden history, lies and rewards.
The Designer calculates the worst-case guess requirement as you edit and refuses to save an unwinnable challenge. Your creations use the same document format and game engine as the built-in set.
£2.99One optional permanent purchaseNo subscription. All 32 included challenges remain free.
Built for iPhone and Android
A complete game before the first purchase.
Thirty-two included challenges, local progress, full rules, no account, no advertising and no analytics. Challenge Designer is the only paid feature.