Selling Str8ts puzzle books as downloads: the straights your buyer builds run by run, trusting every compartment holds true

A Str8ts book punishes a bad file in a way a sample puzzle never shows. Your buyer judges puzzle forty-one, when a compartment of four cells that should hold a straight — four consecutive numbers, in any order — holds 3, 5, 6 and 8 in the key, with the 4 and the 7 nowhere in the run, or a black-cell clue that was supposed to remove the 9 from its row sits one cell off in the printed grid, so the row the buyer is stuck on admits a number the rules say it cannot. Str8ts looks familiar: a square grid, some cells blacked out, a few numbers printed inside the black cells, and digits to fill in everywhere else, like a Sudoku that lost its boxes. Underneath it is a contract in five parts, each part exact. First, the range rule: on an N-by-N grid, every white cell takes a single number from 1 to N. Second, the uniqueness rule: no number repeats in any row and no number repeats in any column. Third, the straight rule: the black cells and the grid edge divide every row and every column into compartments — unbroken runs of white cells — and the numbers in each compartment must form a straight, a set of consecutive numbers with no gaps, in any order; a run holding 6, 8 and 7 is a straight, and a run holding 6, 8 and 5 is not, however neatly it prints. Fourth, the black-cell rule: a number printed in a black cell is a clue, not an entry — that number cannot appear anywhere else in that black cell's row or column, the black cell itself is never filled, and its number is never part of any straight; a black cell with no number is a pure divider and excludes nothing. Fifth, tying it shut: exactly one completion, reachable by deduction alone, with no guessing. A puzzle that breaks any part is not slightly harder. It is false as stated. A good Str8ts book is a verified board: every puzzle re-checked compartment by compartment and line by line from its own key, puzzle by puzzle.

Two warnings belong at the front, because they are the mistakes this genre makes most often, and both start with puzzles Str8ts is not. Str8ts is not Sudoku: there are no 3-by-3 boxes here, and the compartments that replace them are not fixed regions on the page — they are separate runs in each direction, so every white cell belongs to two compartments at once, one horizontal and one vertical, and both must be straights at the same time, over different sets of cells. It is also not KenKen or Calcudoku, the cage puzzles buyers reach for next: a KenKen cage carries an arithmetic target and an operation, and its numbers may repeat inside the cage if the line allows; a Str8ts compartment carries no operation and no target at all — only the promise that its numbers, read as a set, have no gaps — and no number may repeat anywhere in its row or column, compartment or not. And two clauses need saying precisely, because sloppy rules pages ruin this puzzle in two specific ways. A straight is a set, not a sequence: the numbers do not have to run in order along the compartment, so a rules page that shows only ascending examples teaches buyers to reject correct boards, and a setter who generates compartments in order ships a weaker, more predictable puzzle than the rules promise. And the black-cell clue is exclusion only: it removes its number from its row and column, full stop — it does not join a straight, it does not count toward a compartment's length, and a blank black cell excludes nothing at all. Print both clauses, in full, on the rules page, in words a first-time buyer cannot misread: fill every white cell with a number from 1 to the grid size, never repeat a number in a row or a column, make every run of white cells between black cells a set of consecutive numbers in any order, and treat every number printed in black as banned from its whole row and column.

The book is the whole board, not the sample puzzle

Buyers do not buy a grid style. They buy the promise that every puzzle in the file obeys the rules printed at the front, at the difficulty the cover claims, in the order the book presents them. A free sample almost never breaks that promise, because a sample is the one puzzle the setter checked three times. The breakage lives at puzzle forty-one, in the middle of the book, where a generator exported the black cells from one board and the key from the next, or a hand-setter moved one black cell to fix a corner, quietly split one compartment into two and merged two others, and never re-ran a single check. That is why the unit of quality in a puzzle book is the whole set, verified as a set: the same checks, run the same mechanical way, on every single puzzle, with the results kept. If you generated the puzzles, keep the generator's settings per puzzle, including its grid size, its black-cell map, and the clue numbers in those cells. If you set them by hand, keep your solving notes. When a buyer writes in about one puzzle — and in this genre they write in with the page number and the compartment whose numbers they cannot make consecutive without repeating one in its column — you want to answer about that puzzle, not go hunting through a file you can no longer reconstruct.

The rules page is part of the product, not decoration. State all five parts of the contract in plain language, with one small worked example showing a short board being solved compartment by compartment: one single-cell compartment whose number is forced because its row and column leave it one honest digit, one compartment of four where two known numbers, a 3 and a 6, force the run to also contain 4 and 5 — the missing links — before any cell's exact place is known, one black-cell clue whose exclusion empties a compartment's last candidate down to its straight, and the board finishing with every row and column read aloud for repeats. That worked example is the one idea a new buyer must carry away, because Str8ts is solved against sets and lines together, not against single cells, and it is the idea a short rules page most often drops in favour of a pretty picture of a finished grid with no straight ever justified. Most one-star reviews in this genre are not "too hard" or "too easy". They are "the finished board breaks the rules" — and that mismatch is almost always a setter who held the real board in their head, or in the generator, and printed compartments that were never re-checked against their own key.

The contract, part by part

The range and uniqueness rules are the frame everything else hangs on, so check them like one. Every white cell in the key holds exactly one number from 1 to N, every black cell holds at most its one printed clue or nothing, and no number appears twice in any row or twice in any column — counting black-cell clues in that audit as exclusions to verify, not as entries: a clue number that also appears in a white cell in its row is a broken board, not a coincidence. Audit it mechanically, line by line: for each row, list the white-cell numbers and the black-cell clues together and confirm the white numbers are all different and none equals a clue in that line; then do the same for each column. A key that repeats a digit in one column fails here however perfect its straights are, and it is a failure a surprising number of generators produce when a board is transposed or mirrored for variety and one clue travels to the wrong cell.

The straight rule is the heart of the puzzle. Every compartment, horizontal and vertical, read as a set, must be consecutive with no gaps: a compartment of length one is trivially a straight, a compartment of length four holding 2, 3, 4 and 6 is not, because the 5 its length demands is missing and the 6 lies outside any four consecutive numbers that include the 2. This check is purely structural — it can be run on the key compartment by compartment without solving anything — and it catches the classic transcription error where a black cell drawn one position late lengthens one compartment and shortens its neighbour, so two compartments that were both straights become two that are neither, while every row still holds different numbers and the setter's eye slides past. Check compartments in both directions, because a cell sits in one horizontal and one vertical compartment, and each direction catches errors the other cannot see.

The black-cell rule is where clue placement earns its keep, and where keys most quietly go wrong. A clue does three things and only three: it marks its cell as unfillable, it splits the row and the column it sits in into separate compartments, and it bans its number from every white cell in that row and that column. For each clue, confirm all three in the key: the cell is black on both the puzzle page and the key page, the compartments on either side of it are audited as separate straights, and its number appears nowhere else in its row or column. A clue that shifted by one cell between the puzzle page and the key does not merely move an exclusion; it redraws every compartment it touches, which is why clue position is audited as part of the board's structure and not as decoration. Blank black cells get the same position audit minus the exclusion: they divide, and they divide only.

The compartment rule in full is the clause short summaries most often blur, so state it whole: compartments are defined separately in each direction by black cells and the grid edge, a compartment never turns a corner, and a compartment never crosses a black cell. A setter who defines regions instead of runs — treating an L-shaped patch of white cells as one compartment — has invented a different puzzle whose keys will not satisfy buyers solving by the printed rules. For each puzzle, the compartment inventory should be countable from the printed page alone: list every horizontal run and every vertical run with its length, and confirm the key's straights match that list exactly, run for run.

Uniqueness is the part of the contract a plausible board cannot promise. A set of compartments and clues can usually admit more than one completion that respects the range, the lines and the straights if the setter only checks that a completion exists — long compartments are where second solutions hide, because a run of five with a wide-open range can often slide its whole straight up or down by one while a neighbour compensates, and no single line betrays the swap — and a puzzle that solves two ways tells one of its two correct solvers they are wrong. The fifth part therefore has to be proven, not assumed: an independent solve, or a solver run, that counts completions and returns exactly one, with that one reachable by deduction rather than by trying a compartment at two different ranges until one branch survives.

Verification: list every compartment, then list every line

Verification is a separate pass from solving, done mechanically, ideally by a different method than the one that made the puzzle. Solve each puzzle once as a buyer would, by deduction only, and keep the solve honest: if you guessed a compartment's range, and the guess worked, that puzzle has not been shown to have one solution, and it goes back. Then run the structural audit on the key, in this order. One: inventory audit — every black cell, every clue number and every grid dimension on the puzzle page appears on the key page, in the same position, unchanged. Two: range audit — every white cell in the key holds one number from 1 to N, and no black cell is filled. Three: line audit — no number repeats in any row or column, and no white-cell number equals a black-cell clue in its row or column. Four: compartment audit — every horizontal and every vertical run of white cells, read as a set, is consecutive with no gaps, with the run list taken from the printed page, not from the generator's memory. Five: clue audit — every clue's exclusion holds across its whole row and column, and every blank black cell is treated as a divider only. Six: givens audit — no clue was moved, added, dropped or renumbered between the puzzle page and the key page, and no black cell shifted by a cell. Seven: uniqueness audit — a second, independent solve, or a solver run, that counts completions and returns exactly one. Eight: consistency — puzzle page, key page and any thumbnail or marketing sample of that puzzle are the same puzzle, with the same black-cell map, the same clues, and the same completion in the key.

Keep the audit results with the book's files, puzzle by puzzle. When a corrected edition ships, that record is how you know which puzzles actually changed and which were only suspected. It is also how you answer the buyer who found a real error: not with an apology and a shrug, but with the corrected puzzle, the audit lines that now pass, and the corrected file sent to everyone who bought the book — which is where the delivery side of this business, covered below, stops being administration and becomes the difference between a one-star review and a loyal repeat buyer.

Difficulty is compartment shape and range pressure, not just grid size

Grid size is the weakest difficulty lever in Str8ts, and the one covers lean on hardest. A large grid whose compartments are short and whose black-cell clues ban the awkward numbers early can fall run by run in a satisfying sweep, while a small grid with one long compartment whose straight could sit at three different ranges, and few clues, can stop an experienced solver cold. The real levers are these. Compartment length: short runs are pinned quickly — a run of two is one of a handful of pairs — while a run of five or six carries a wide range of candidate straights, and a book can be graded by the lengths it mixes at each stage. Range pressure: how narrow each compartment's honest range is once its known numbers and its lines' exclusions are applied — a run known to contain 3 and 6 at length four is already solved as a set, while a run with no known numbers is a range waiting for pressure from crossing compartments, and that waiting is this puzzle's signature late difficulty. Clue density: black-cell clues do double work, splitting compartments and banning numbers, so a board generous with clues is usually easier than its size suggests, and a sparse board leaves ranges floating until cross-pressure builds. Crossing pressure: every cell sits in two compartments, and boards where the horizontal and vertical runs constrain each other early solve kindly, while boards where one direction stays silent until the other is nearly finished are harder at any size.

Grade a book by testing solves, not by measuring grids. Time honest solves across the set, note where each puzzle's deductions stall and restart, and order the book so difficulty genuinely climbs — early puzzles with short compartments, helpful clues and ranges the known numbers pin down at once, later puzzles with long compartments, sparse clues and ranges that only settle under crossing pressure near the end. Print the grading honestly: "easy" should mean the straights mostly declare themselves, not merely that the grid is small. A buyer who trusts your grading buys the next volume; a buyer who was ambushed by a floating six-cell run on page three of the easy book leaves a review about that instead.

Print honesty: the page is the interface

A Str8ts page is read in pencil first and pen last, and the print has to survive both — starting with its black cells, because solid black cells carrying white clue numbers are this genre's whole interface. A black cell must print as unmistakably black after a photocopy, at arm's length, in greyscale, and its clue number must stay legible as white on that black: a clue that greys out, fills in or vanishes on a home printer removes an exclusion and a divider at once, and the buyer is then solving a different board from the one the setter checked. Compartment structure must be readable without the key: a buyer should be able to count every run's length off the printed page, so cell borders need enough weight to survive copying while never rivalling the black cells themselves — if a bold cell border can be mistaken for a black divider, runs merge in the buyer's eye that are separate in the key. The digits a buyer writes need room too: cells must be large enough for a pencilled digit plus the small candidate notes Str8ts solvers keep — the possible range of a compartment is usually pencilled along its cells before any digit is committed — with space that survives a second erasure. Your key must print the finished grid at the same size relation to the puzzle page, with the black cells and their clues still visible in the key, so a buyer can re-audit any compartment and any line for themselves instead of taking the picture on faith — in this genre the key that greys out its black cells cannot be checked, and an uncheckable key reads as an untrusted one.

Proof the final PDF, not the working file. Export at the exact trim size, print one puzzle and its key on a home printer at 100 percent, and solve the printed puzzle with the printed rules page as your only reference. Check the three things screens hide: whether black cells still read as black, with legible white clues, after the page has been photocopied once — classrooms and puzzle clubs will photocopy it — whether every compartment's length can be counted unambiguously off that same copy, and whether there is room in each cell for a pencilled digit plus candidate notes. If a puzzle needs a screen's zoom to tell a clue number from a smudge, it is not ready to be a download.

Licensing, provenance, and the download itself

State the licence where the buyer decides, not buried after purchase: who may solve the puzzles (one person, a household, a classroom, a club, a care setting), how many copies they may print, whether a teacher may hand a page to thirty students, whether a club may run one puzzle as a group activity, and whether the file itself may be shared, resold or republished — and say plainly that sharing the file is not the same as sharing a printed page. Puzzle books are bought heavily by teachers, club organisers and carers, and those buyers are trying to comply; a licence they cannot find reads to them as a licence that says no. Say how the book was made, too: hand-set, software-generated and hand-checked, or software-generated and mechanically audited — and state your conventions in the book and in the listing, including the name itself: this puzzle appears both as Str8ts and as Straights, so say plainly that they are the same puzzle under the same rules, that a straight is a set of consecutive numbers in any order, and that black-cell numbers are exclusions, never entries, because a buyer raised on Sudoku boxes or on KenKen cages will otherwise judge your correct boards as wrong ones. Provenance is not an apology — in this genre it is a quality claim, as long as it is specific. "Generated, then every compartment listed and every line counted from its own key" is a claim a buyer can weigh; "high quality puzzles" is not.

Delivery is the last part of the contract. The buyer should get the file immediately, from a link that works the first time, on the device they bought it on, with re-downloads available when — not if — they lose it. Send a corrected edition to every past buyer when one ships; do not wait for them to discover the errata the hard way. I run my own download delivery through FileFreight — flat monthly pricing instead of a cut of every sale, expiring links, and updated files reaching past buyers without me re-emailing attachments by hand — but whatever you use, test it as a buyer: pay, receive, download, lose the file, recover it, and receive an update, before you ask strangers to trust it with money.

The launch checklist

1. Every puzzle solved by deduction alone — no guessed compartment range in any solve, start to finish.
2. Range and line audits passed: every white cell holding one number from 1 to N, no number repeated in any row or column, and no entry matching a black-cell clue in its line.
3. Compartment audit passed: every horizontal and vertical run of white cells, listed from the printed page, holding a set of consecutive numbers with no gaps.
4. Clue audit passed: every black cell in the same position on puzzle and key pages, every clue's exclusion holding across its whole row and column.
5. Uniqueness audit passed: an independent solve or solver run returns exactly one completion for every puzzle.
6. Print proof passed: black cells solid and clues legible white-on-black at 100 percent after one photocopy, compartment lengths countable, cells roomy enough for digits and candidate notes.
7. Licence, provenance and naming conventions stated in the listing and the book, the delivery flow test-bought end to end, and a corrected-file path ready for every past buyer.

A Str8ts book is a promise that a grid of black cells, clues and compartments means exactly what its rules page says, on every page, in every run, in both directions. Keep that promise mechanically — list the compartments, count the lines, prove the one solution — and the file you deliver is the book the buyer thought they were buying.