A masyu book punishes a bad file in a way a sample puzzle never shows. Your buyer does not judge the tidy grid in the listing image. They judge puzzle forty-one, deep into a larger grid, when the single loop they have been drawing cell by cell reaches a white circle the loop cannot pass straight through without breaking the turn the rules demand beside it, or closes a neat little circuit in one corner while half the grid still waits outside it — because one circle was printed white that should have been black, or a black circle was left pale enough to read as white, or the key quietly draws a second, separate loop the puzzle page never allows. That is not a puzzle they can skip cleanly. A masyu is a contract in three parts: one single loop, drawn through the centres of cells, that never crosses itself, never branches, and never touches itself except where it joins to close; white circles the loop must pass straight through while turning in at least one neighbouring cell; and black circles the loop must turn inside while passing straight through both neighbouring cells. One broken part does not make the puzzle slightly harder. It makes it false as stated, discovered only after a buyer has drawn half a page on the strength of it, and a careful solver blames their own line first. A good masyu book is a verified set: every circle obeyed exactly, every puzzle holding exactly one loop, every key re-drawn against the final page, and every difficulty label graded on grid size, circle density, the balance of black and white circles, and corridor and region structure together.
The book is the puzzle set, not the sample grid
Buyers do not solve your listing image. They judge it by whether each grid can be finished as stated, with one loop, no branches, and no circle left disobeyed.
Ship the book as a first-class solving experience, not one sample grid with the rest implied. Name exactly what the download contains. If the book holds eighty puzzles, say the count plainly, name the grid sizes it really holds — small starter grids, medium standard grids, and larger challenge grids if you ship them — and say how many puzzles sit in each difficulty band claimed, because a buyer who bought gentle grids has not bought sprawling challenge grids. State the cell system honestly: the grid is made of empty cells the loop may pass through or leave unused, and some cells carry a circle — white or black — and the buyer should never have to wonder whether a pale circle is a white clue printed faintly or a black clue that lost its fill in layout. Say whether every cell must be used or whether the loop may leave cells empty — in standard masyu it may, and a buyer told otherwise will force the line into corners it was never meant to visit. Say whether full answer keys are included for every puzzle and where they live — at the back, on the following page, or in a separate file — before purchase, because a finished loop glimpsed mid-solve spoils the work, while a grid with no key leaves a completed drawing unconfirmed. Say whether any puzzles use special rules — a variant shape or a regional twist — and where. State the page size the file assumes and whether it is meant for print, screen, or both. Put the rules on an instruction page the buyer opens first: draw one loop through cell centres, the loop never crosses, branches, or touches itself except to close, white circles go straight with a turn beside them, black circles turn with straights on both sides, what the difficulty bands mean, and how the keys are marked — before puzzle one. Check the solving as the buyer experiences it: download it fresh, print it, and draw one full section with no help from your source files.
Every claimed puzzle has exactly one solution: the promise a masyu book has to keep
A masyu buyer cannot improvise around a defective grid. A circle printed in the wrong colour, a second valid loop the empty cells quietly allow, or a layout whose only completions close a small circuit early and strand the rest of the grid does not make the book slightly harder. It makes it untrue in a way patience cannot fix.
Hold every puzzle to the contract, with no loose readings. First, the solution is a single loop: a closed line drawn through the centres of cells, moving only orthogonally — up, down, left, right, never diagonally — that never crosses itself, never branches, and never touches itself except where its two ends join to close it. A drawing with a spur, a crossing, a T-junction, or two separate circuits is not a near miss. It is not a solution at all. The loop does not have to visit every cell, but every cell it does visit it enters once and leaves once, by two different sides. Second, white circles: the loop goes straight through the cell holding a white circle — in one side and out the opposite side, no turn inside that cell — but it turns in at least one of the two adjacent cells, the cell immediately before the circle on the loop and the cell immediately after it. At least one of those neighbours bends; both may bend, but neither may be skipped — a loop that runs straight through a white circle and straight through both cells beside it has broken the rule even if the rest of the drawing is perfect. Third, black circles: the loop turns in the cell holding a black circle — in one side and out an adjacent side, a right angle inside that cell — but it goes straight through both adjacent cells, the cell immediately before the circle and the cell immediately after it, with no turn in either. A loop that turns inside a black circle and also turns in a neighbouring cell has broken the rule just as surely as one that runs straight through the black circle itself. Fourth, exactly one solution. Not one intended loop — one loop, full stop. A grid that admits two different single loops, each satisfying every circle, has broken the promise on the cover — the buyer who finds the second loop has discovered the puzzle was never verified.
Prove all of it mechanically. Re-solve every puzzle from the final laid-out pages, checking that the drawn loop is one closed circuit with no crossing, branch, or self-touch, that every white circle is passed straight with a turn in at least one adjacent cell, that every black circle is turned in with straight passes through both adjacent cells, and that no second loop satisfies the same circles. Do not trust the generator or your memory. Circles mutate in editing — a fill dropped in resizing, a circle shifted by one cell in re-layout, a white printed where a black belongs — and a puzzle valid in the spreadsheet can be broken in the PDF. Test the truth the way a buyer will: solve each puzzle cold, without the key, then run a second, independent pass — a solver program solving from the printed circles alone, a fresh manual solve on a different day, or a different solver altogether — and confirm both passes land on the same single loop. Re-running the same generator is not a second pass. Note every puzzle where it found a second loop, an early-closing circuit, a white circle with no legal turn beside it, or a black circle whose straight neighbours cannot both be honoured — that list is your defect list, fixed before release.
Complete and consistent: the loop, the circles, the grid, and the answer keys that must agree
A masyu book is a three-way system — the puzzle the buyer draws in, the circles, grid, and difficulty label that give the solve its contract, and the answer key that proves the contract can be fulfilled in exactly one way — and any inconsistency among the three reads as carelessness in a product whose whole value is trust.
Deliver the set in a stated, checkable order. Number every puzzle, keep the numbering identical on the puzzle pages, in any contents or difficulty index, and in the answer section, and never renumber silently between editions: a buyer halfway through version one who downloads your corrected version two must find puzzle forty-one in the same place, or your fix has cost them their progress. Keep the circles identical everywhere: the circles on the puzzle page are the clues the key must honour, a cell printed with a black circle must be turned in by the key's loop with straight cells on both sides, and a key that runs straight through a printed black circle, or turns inside a printed white one, is not a rounding difference — it is the book arguing with itself.
Run the loop, circle, and grid consistency checks as their own pass, separate from solving. For the loop: every segment runs centre to centre between orthogonally adjacent cells, no segment crosses another, no cell carries more than two loop segments, no cell the loop visits is entered and left by the same side, and the finished drawing counts as exactly one circuit — trace it from any cell and you return to your start having covered every drawn segment, with nothing left over. For the circles: every white circle is checked on both sides — straight through its own cell, a turn in the cell before it, the cell after it, or both — every black circle is checked the same way in mirror image — a turn in its own cell, straight through the cell before it and straight through the cell after it — edge and corner circles are checked with special care, because a circle near the border has fewer neighbours to satisfy it, and every circle is confirmed present, in the right cell, and in the right colour rather than a clue that drifted or faded in layout. For the grid: row and column counts match the stated size, no cell is half one size and half another at a layout seam, the outer border closes, and circles at the edge sit fully inside their cells, not clipped by the frame.
Check every key against the final printed pages, because a re-laid-out page keeps its clean looks while silently invalidating the loop promised. The keys deserve the same care as the puzzles: print each solution as the completed grid in the same size and orientation as the puzzle, circles still showing in white and black and the loop drawn clearly through them, so the buyer can compare segment for segment and trace the circuit circle by circle, and arrange the keys so checking puzzle twelve does not force a glimpse of puzzles thirteen and fourteen. Never let the key be checked by trusting it. Check it by tracing against it: start anywhere, follow the loop until you return to your start, confirm you used every segment exactly once, confirm no second circuit hides in a corner, and verify every circle by its rule as you pass it — straight and a neighbouring turn for white, a turn and two neighbouring straights for black. If you include worked help, every claim must be true of the puzzle it describes. Test the way a buyer will: pick puzzles from the back half, solve them cold, then compare against the printed key segment for segment. That audit is the closest thing this genre has to a guarantee.
Difficulty is more than grid size: circle density, the black-white balance, and corridors
Grade difficulty honestly, and by more than how many rows a grid has. Four levers work together in masyu, and a book that labels its bands by size alone will mislead the buyers who trust its labels most.
The first lever is grid size. A small grid gives the buyer fewer cells to route a loop through and fewer circles to keep satisfied at once, and it is where a new solver learns what a white circle's neighbouring turn and a black circle's neighbouring straights actually demand. A larger grid multiplies regions, hides consequences further from the circle that causes them, and asks the buyer to hold several half-drawn stretches in mind at once, including stretches that must not be allowed to close early. Size matters — it just does not decide difficulty on its own.
The second lever is circle density: how many circles the grid carries, and where they sit. A sparse grid leaves long stretches of empty cells where the loop's route is barely constrained, and the work is keeping a single circuit possible at all — every early commitment can quietly forbid the only route home. A dense grid pins the loop down in place after place, each circle forcing a straight or a turn, and the work is reconciling demands that collide two cells apart. Say which pattern your harder bands use.
The third lever is the balance of black and white circles. A black circle is a tight, local instruction: it fixes a turn in its own cell and straights in both neighbours, so three cells of the loop are settled the moment it is read. Those clues anchor a solve and give it a starting place. A white circle is a looser instruction spread over the same three cells: straight through its own cell, a turn in at least one neighbour — but the buyer must still decide which neighbour, or whether both turn. A grid rich in black circles can be large and still feel guided, because the solve starts in a dozen definite places. A modest grid dominated by white circles can feel empty of handholds, because almost every turn must be inferred from keeping the loop single and unclosed. Neither is automatically harder — but they are different kinds of hard, and a label that hides the difference is not a label, it is a guess.
The fourth lever is corridor and region structure: the shapes the grid's edges, clusters of circles, and empty regions create. Long open regions reward one well-routed stretch and punish any small circuit, because a loop that closes early strands everything outside it. Narrow passages between circle clusters, single-file gaps near the border, and corners only one route can serve create the characteristic pressure — a stretch drawn from only two directions, one of which would seal a region off from the loop forever. A black circle mid-region constrains three cells at once; in a corner, a quieter neighbourhood. Grade on what actually made a puzzle hard — size, density, the black-white balance, and corridor and region pressure — and never promote a puzzle to a harder band simply to fill a quota.
Print, pencil, and eyes: what the page does that the preview cannot
The grid a buyer approves on a bright phone screen is not the grid they solve on paper, and masyu makes the gap physical: the buyer finishes the puzzle by drawing a loop through cell centres, trying light trial segments, and erasing stretches that would close the circuit too soon, and the printed page is the buyer's only truthful reference once the screen is off. State the printed page size the file assumes, and tell the buyer to print at 100 percent, actual size, with fit-to-page off, because a shrunken page is not a cosmetic change: a large grid scaled down squeezes cells until a drawn loop segment, a faint trial mark, and a printed circle stop being distinguishable.
Print circles with honest legibility. A white circle must read as a clean ring — a visible outline with an empty middle — at final print size on a tired home printer, because the entire rule turns on knowing instantly which colour a circle is. A white circle whose outline prints broken or hair-thin invites the buyer to miss the clue entirely and draw straight through both its neighbours. Test the densest grid on the worst printer you can reasonably expect.
Hold the black-versus-white contrast without mercy. A black circle must print as solidly, evenly filled — deep black with no pale centre — because a black circle that prints grey is a white circle's evil twin: the buyer will turn beside it and run straight through it, solving faithfully against the wrong rule for an entire sitting. Check the pair side by side on paper: any page where a faded black and a clean white could swap readings in poor light is a page to re-lay out, with heavier fill for black circles and a bolder ring for white ones, before any buyer sees it.
Print grid lines with a weight that does the job and no more. Lines must stay visible so rows, columns, and regions can be traced without drifting into the next cell, heavy enough that a circle sitting in a cell stays readable under pencil marks, and never so heavy that the lines crowd the centre of each cell, where the loop itself has to be drawn. Where a circle sits near a cell edge, the buyer must still be able to tell which cell holds it, because a straight-or-turn judgement for its neighbours depends on knowing exactly which cells are before and after it on the loop.
Leave honest pencil room for the loop. A buyer needs room inside each cell to draw a clear segment through its centre, to add a small trial mark, to note a cell the loop must avoid, and to erase a stretch cleanly without tearing away the printed circle beneath it. Cramped cells punish careful solvers and make a half-erased trial segment look like a committed one. If you sell a large-print edition, say what is actually larger — cells, circles, grid, keys — and solve one full printed puzzle yourself before you decide the page is ready.
Licensing a masyu book is licensing the solving
Solving feels private, yet the same file could supply a family's evening, a teacher's logic lesson, a puzzle club, a care home's activity hour, or another seller's new puzzle book. If your terms do not answer those uses in advance, the buyer either asks and waits, or guesses and infringes.
Answer the questions buyers actually ask, in short sentences inside the download, and keep personal solving, group use, and republication separate. May the buyer print the book more than once for their own use — a second clean attempt after a solved copy covered in loop segments and erased trial lines? Say yes or name the limit, because a marked-up grid is a spent grid, and reprinting is the genre's normal life: a buyer who cannot print a fresh copy has bought a single-use product wearing a book's clothes. May they print copies for family, a classroom, a club, or a care setting, free of charge? Each needs its own answer, and if group use needs an extended licence, name and price it before purchase. May a buyer share their own solved grids — a photograph of a finished loop, a video of a solve? Say so exactly, separate from the file itself: what is plainly out is reselling or giving away the digital file, and republishing the collection as a competing book where your terms prohibit it.
Handle provenance with particular care, because masyu puzzles arrive by two very different roads. If your grids were generated, say what generated them and what check confirmed each one — the solver pass, uniqueness test, loop-tracing verification, and circle audit — and keep those records, because the generator said so is not a verification trail. If your puzzles were hand-made, or licensed from a collection, state the terms in your records — whether they may appear in future volumes, whether the licence covers the answer keys as well, and whether the grids are cleared for republication — and do not imply a right to republish puzzles you have not cleared.
A second loop cannot be un-drawn: the errata rule and the version line
Every genre has an error that cannot be taken back, and a masyu book's is trust in the circles: a buyer who solved honestly for forty minutes and then discovered the only possible line closes into two separate loops cannot get that solving back, and a solver told, kindly, that they just need to think harder has been taught to doubt a logic that was right all along. A wrong circle voids the puzzle it sits in — not the page, the puzzle — and the correction is not a footnote. It is a replacement, sent as a corrected file to every buyer.
Run corrections as a stated system, not an apology when someone complains. Your errata rule is simple and it covers the failures only this genre makes: a second loop — a puzzle whose circles admit a second, different single loop as well as the key's — a circle rule gone unsatisfiable — a white circle whose straight pass leaves no adjacent cell able to turn, or a black circle whose turn leaves no way to run straight through both neighbours — or a key loop mismatching a circle — the printed key running straight through a black circle, turning inside a white one, or closing as two circuits — each triggers the same response: a corrected file to every buyer. Keep a public errata list, dated by edition, naming the puzzle numbers affected and what changed — a puzzle replaced because it admitted a second valid loop, a puzzle replaced because a white circle's rule could not be satisfied by any single loop, a circle corrected because its printed colour did not match the loop its solution requires, a circle restored because a clue missing in layout left a stretch of loop unconstrained, an answer key re-drawn, a difficulty label fixed — so a buyer with an early copy can check in minutes before they solve, the only moment a correction can still save the drawing. Version the file: put the edition and date inside the download, and never silently change a circle's colour or move a circle by a cell. When one wrong circle is confirmed, re-solve the whole book, not only the reported puzzle, and say what the re-checking covered. Notify past buyers: the file a new buyer receives must always be the corrected edition, and past buyers should fetch the update without digging through old email. Be honest in the listing while a known defect is unfixed.
A short launch checklist for masyu book sellers
Before the listing goes live, work through the book as a buyer will — on paper, in order.
- Download your own file fresh and print it at 100 percent, actual size. Solve from that printout only, pencil in hand, and draw, try, and erase loop segments as you go.
- Re-solve every puzzle mechanically on the final laid-out pages: one single loop through cell centres with no crossing, branch, or self-touch, every white circle passed straight with a turn in at least one adjacent cell, and every black circle turned in with straight passes through both adjacent cells. Fix every broken circle before release.
- Check uniqueness by a second, independent pass, not by trusting the generator: confirm no puzzle admits a second valid loop, and confirm every printed answer key is the one loop.
- Audit the three-way agreement on the final pages: loop, circles and grid and difficulty label, and answer key must agree exactly — one circuit when traced, every white circle straight with a neighbouring turn, every black circle turned with two neighbouring straights, no missing or mis-coloured circles; if you ship hints, every claim in them must be true of the puzzle described. Solve a random sample from the back half cold, then compare against the printed key.
- Confirm the listing states the puzzle count, the grid sizes, the difficulty bands and what they mean — grid size, circle density, black-versus-white circle balance, and corridor and region structure — and where the answer keys live.
- Check the page with your own eyes on the largest grid: white circles reading as clean rings, black circles solid enough to survive a tired printer, no faded black that could be misread as white, grid lines clear without crowding cell centres, and real pencil room to draw a segment through a centre, try a stretch, and erase cleanly. If a circle can be misread, re-laying out beats a buyer's frustration.
- Put the licence in the download in short sentences — repeat printing for personal use, family, classroom, club, and care-setting use, sharing solved grids, puzzle provenance for generated and hand-made grids, and the file-sharing line, each answered separately — and start the errata page and the edition line inside the file on day one.
A closing note on delivery: FileFreight is one option for that delivery step: flat-rate download delivery plus license keys on your own Stripe, so payments settle into your own Stripe account — it is not a tax or merchant-of-record service, not a payment processor in its own right, it does not handle tax, it has no importer, and it is not a Shopify app. Check every circle, close the one loop — and let delivery be the one part a solver never thinks about.
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