How to Master Mastermind Deduce
TLDR: Mastermind Deduce shows you a history of past guesses and their peg feedback. Exactly one code survives every constraint. Find it by building a colour inventory, locking positions with black pegs, and verifying your answer against every row before you submit.
What You Are Actually Doing
Mastermind Deduce is not a guessing game. Every round shows a history of past guesses and their black/white peg feedback. Exactly one candidate code - out of the no-repeat space of 6 colours across 4 pegs (360 total permutations) - is consistent with every row. Your job is to find that one survivor.
There is no randomness in your decision. The answer already exists. Your only task is to read the constraints correctly and narrow the space down to one.
The validator is absolute: a pure function called verifyFinalDeduction replays the full history against all 360 permutations and checks whether your chosen code is the unique survivor. If it is, you are right. If even one other code also satisfies every row of feedback, or if your code fails any row, you are wrong. There is no bluffing or getting lucky.
Reading the Peg Feedback
Before you can deduce, you must read feedback fluently.
A black peg means one peg in that guess is the correct colour in the correct position - a perfect match on both axes.
A white peg means one peg is the correct colour but in the wrong position. The colour exists somewhere in the secret code, just not at the position where you guessed it.
The critical rule: the order of the pegs in the feedback tells you nothing about which positions they came from. If feedback is “two black, one white,” somewhere in that guess there are two perfect matches and one out-of-position match - but you do not know which positions are which. That ambiguity is the core difficulty.
Example: you guess RGYB and the secret is BYRG. G at position 2 is correct colour and position (one black). Y at position 3 is correct colour but wrong position (one white). B at position 4 is correct colour but wrong position (one white). R at position 1 is absent. Feedback: one black, two white. Without further rows, you cannot tell which position holds the black.
Peg counts, not positions: “Two black, one white” tells you the count of matches, not where they sit. Your job is to find the assignment of colours to positions that produces the exact feedback count in every single row.
Core Skill: Constraint Stacking
Each row of history is a hard constraint. Stack them and the surviving space shrinks fast.
If a row shows “guess RGYB, feedback 0 black 0 white,” all four colours R, G, Y, B are completely absent from the secret code. That single row eliminates roughly 270 of the 360 permutations immediately.
If a row shows “guess RGYB, feedback 1 black 0 white,” exactly one of those four colours is in the code and in the right position. The other three are absent. Now you need to figure out which one.
After four or five rows, the surviving space typically collapses to one code. The best players develop an intuition for which combinations are forced - they can feel which codes are impossible without consciously walking through every elimination.
Colour inventory first. Before touching positions, build a two-column list: colours that must be in the code (appeared in feedback as black or white) and colours that are banned (appeared in a guess with zero feedback). This step alone cuts the search space by an order of magnitude. Then worry about placement.
Concrete Tactics
Lock Positions with Black Pegs
Black pegs are your certainties. If a row gives one black peg and you can figure out which colour is in the right position, mark that cell as solved. Use subsequent rows to verify: if that colour appears in the same position in another guess and still generates a black peg, you have confirmed it.
Conversely, if a colour appeared at position 2 with a white peg, you know it is in the code but not at position 2. Combined with another row showing it is not at position 1 or 3 either, you can pin it to position 4 by elimination.
Stack the white peg exclusions: Each white peg tells you a colour is in the code and not at a specific position. Collect these across rows. When a colour has been excluded from positions 1, 2, and 3 by white pegs in different rows, it must be at position 4.
Use Zero-Feedback Rows as Bans
A row with zero black and zero white pegs is gold. Every colour in that guess is completely absent from the secret code. This is the fastest way to shrink the colour inventory. If you see two such rows, you may have ruled out five or six colours entirely, leaving only one or two possible colours for each position.
Zero rows first. When scanning history, locate zero-feedback rows before anything else. The colours in those guesses are banned. Write them down mentally. Every other row can now only produce feedback from the remaining colours, which dramatically constrains your search.
Verify Your Answer Before Submitting
Before you pick a code, mentally replay it against every row. Ask: does this code produce the exact feedback count shown in row 1? Row 2? Row 3? A single failed row means your candidate is wrong and you need to keep searching.
Skipping this step is the most common way to get the streak ended by a careless error on a puzzle you essentially solved.
Always verify before submitting: Pick your candidate, then replay it against the full history. If it passes every row, submit. If it fails any row, it is not the survivor - keep narrowing. One minute of checking beats one reset.
Common Mistakes
Misreading White Peg Exclusions
A white peg at position 2 means the colour is in the code but not at position 2. It does NOT tell you the colour is at position 1 or 3 specifically. New players often narrow incorrectly by assuming white means “adjacent position.” Hold the exclusion loosely until other rows narrow the remaining positions.
White peg rule: A white peg excludes one position for that colour. It says nothing about which position is correct - only which one is not. Accumulate exclusions across multiple rows to pin the colour to its true position.
Forgetting the No-Repeats Rule
The secret code has no duplicate colours. With 6 colours and 4 pegs, every peg is a different colour. Codes like RRYB or RRYY are impossible. This eliminates many spurious candidates quickly. When you have narrowed the inventory to four colours and are arranging them into positions, you only need to consider permutations, not combinations with repeats - that is 24 arrangements, not 256.
Over-committing to a Hunch
After two or three rows you may feel certain about one position. Resist locking it in mentally before you have verified it. Hunches survive until a later row proves them wrong, and a wrong hunch cascades into wrong conclusions everywhere else. Trust the evidence, not the feeling.
Evidence over intuition: If you feel certain about a position but have not explicitly verified it against every row, you have not proven it. One misread row can send you chasing a wrong survivor for minutes. Check the evidence first.
Practice Routine
Rounds 1-5: Read the feedback aloud. For each row, say the constraint it creates out loud: “row 1 bans R, G, Y, B entirely” or “row 2 means exactly one of R, Y, B is in position 3.” Verbalising forces precision.
Rounds 6-15: Build the inventory first. Before looking at any position, extract the full colour inventory from all rows. Which colours are banned? Which must appear? Only then move to position analysis. This habit prevents the common mistake of solving positions with an incomplete colour set.
Rounds 16+: Time yourself. Target two minutes per puzzle. Speed comes from recognising constraint patterns faster, not from skipping steps. If you miss, identify exactly which step broke down and repeat that step consciously in the next round.
Progressive pressure. Slow deliberate rounds build the constraint model. Timed rounds build speed within that model. Cycle between them: five slow rounds to sharpen the method, five timed rounds to compress it. Repeat monthly to stay accurate under pressure.
Why This Game Trains Real Logic
Mastermind Deduce is cheat-proof. The only path to a correct answer is actual deduction. You cannot pattern-match past rounds, guess randomly, or rely on luck - the validator checks every constraint simultaneously.
This trains the core of formal reasoning: holding multiple conflicting rules in memory, eliminating impossible cases systematically, and converging on the one inevitable answer. The same skill appears in debugging code, solving logic puzzles, evaluating arguments, and following any chain of evidence to a conclusion.
The game also trains directional discipline: working forward from evidence to conclusion, not backward from a preferred answer to a justification. That direction is easy to reverse under pressure and genuinely difficult to maintain. Every streak you build here is proof you held it.
After a long streak: Try explaining your reasoning out loud for one puzzle. Verbalising the constraint chain - “this row bans G, that row puts Y in position 3, so position 1 must be B” - cements the model and reveals gaps in your logic faster than silent solving.
Mastermind Deduce
Crack the secret code from past guesses and peg feedback. Pure deductive reasoning, cheat-proof validation
Play nowWorks on any device.
