How these are built
Ten digits make a harder fill-in than twenty-six letters
A fill-in is solved by checking: which of the words of this length fits the letters already crossing it? With words, the answer is usually one of 3.3 on a Hard sheet. With numbers it is one of 5.4, because a digit written in a crossing square rules out far less than a letter does. Same grid, same rules, and the alphabet is the difficulty.
The level is how many words you have to check, and it is measured
Nearly every step in a fill-in is the same step: look at a slot, count its squares, read the letters already crossing it, and find the one word on the list that fits. What changes between an easy sheet and a harder one is not the step but its width, meaning how many words of that length are still on the list when you do it. The generator records that width for every placement in a solve and uses the average to tell Easy from Medium, rather than a guess about what feels harder.
Three levels, because the fourth technique was almost never needed
The solver inside this page carries a ladder of four deductions, cheapest first: one word fits a slot; one slot is left for a word; the letters a crossing square could take, reasoned from words not yet placed; and a trial that follows a word until the grid breaks. Every sheet is solved on that ladder before it is printed, and a puzzle that finishes has proved its answer unique, because no rung ever discards a word that appears in a real solution.
| Level | What it makes you do | Starter words | Checked per slot, words | Checked per slot, numbers |
|---|---|---|---|---|
| Easy | The longest word is printed in for you, lengths are spread out, and every step is a slot with one word that fits. | 1.2 words · 1.7 numbers | 1.8 | 2.3 |
| Medium | No word is printed in unless the grid needs it, more words share each length, and you may have to turn a word round and ask where it can go. | 0.3 words · 1.2 numbers | 2.5 | 4.7 |
| Hard | At some point no slot has one fit and no word has one place. The way through is the letters a crossing square could take from words not yet placed. | 0.0 words · 0.3 numbers | 2.1 | 3.2 |
Read from the engine at build time, 6 sheets per cell. Starter words are the entries printed into the grid before you begin: Easy always prints its longest word, and every level adds one only where the grid would otherwise have two answers. Hard is not defined by the checking width and can measure below Medium on it; what makes it Hard is the crossing step, which the two levels below are never allowed.
Why the page does not offer an Expert level
The obvious design was four levels, one per rung, and it was built and measured first. The second and fourth rungs turned out to be needed on a small minority of sheets however the generator was steered: once a few letters are written into the grid, some slot nearly always has exactly one word that fits, and the trial-and-break step almost never gets a turn. On Hard word sheets it fires on 0% of grids and on Hard number sheets 0%. A level named after a step its sheets do not take would be a label, so there are three levels and each means something you will notice with a pencil. Hard is the one that is different in kind: it is only offered when the sheet cannot be finished with the two cheap steps, and on this size that holds for 100% of word sheets and 100% of number sheets. When a small grid with a short list cannot be made Hard, the builder says so under the preview rather than printing the label anyway.
What the two ends of the range look like
The Easy sheet prints its longest word and spreads its lengths, so the first move is reading the grid rather than searching the list. The Hard number sheet prints nothing, shares its lengths on purpose, and somewhere in the solve every open slot has more than one number that fits: the way through is to notice that whatever goes in one slot puts a digit in the shared square, and only some of the other slot's numbers can match it.
The list is sorted so it cannot give the answer away
The grid is grown one word at a time, each new word crossing one already there, and the order they went in is a map of the layout: the first word is the long spine across the middle and its neighbours follow. So the list is never printed in that order. It is grouped by length and sorted alphabetically within each group, which is also the order a solver wants, because the first question on any fill-in is which lengths appear only once.
Three checks every sheet passes before it prints
- Every word is on the grid exactly once and no square belongs to a word that is not on the list. The slots are read back off the finished grid rather than trusted from the placement, so an accidental two-letter run beside a word would fail the sheet rather than print as a mystery entry.
- The fit is unique, by proof rather than by search. The logical solve that grades the sheet only ever removes a word from a slot it cannot occupy, so reaching the end is the proof. When a layout comes out with two answers, a word is printed in as a starter until it has one, and the starters are then stripped again so only the ones the grid needs survive.
- Your own list is used as written, and anything dropped is named. A custom word shorter than three letters, longer than the grid, or repeated is left out and listed under the preview with the reason. A word that fits the rules but could not be crossed into the layout is reported the same way, so a list of twelve that prints eleven never does so silently.
How to solve one, if you never have
- Count the squares in every slot and note the lengths. Then read the list: any length that appears once on the list goes straight in.
- Every word you place writes letters into the slots crossing it. Go to those slots next, because they are now the easiest.
- For a slot with letters in it, check only the words of that length. Usually one fits. Cross it off the list.
- If no slot has a single fit, turn it round: pick a word and ask where it can still go.
- On Hard, look at a crossing square and ask what letters each side could still put there. Only the words that agree on that square survive.
What this page does not do
It is not a crossword. There are no clues and nothing to know, which is why it suits vocabulary practice and spelling lists so well and why it does not replace a clued grid. Crossword is on the roadmap as a separate build with its own clue bank.
Theme lists run from four to twelve letters, so a small grid with a short list cannot always share enough lengths to be Hard; the builder counts those sheets and says so. Number sheets never print a number with a leading zero, because a solver reading "0417" has to decide whether that is a four-digit entry, and a rule the solver has to guess at is a rule the sheet has failed to state.
How this page is made and checked
Print Puzzles is part of the Hamilton Digital Media Limited puzzle network. This page is written and reviewed by Brian Hamilton and Karan Hamilton. The engine was checked with a build-time harness that generated sheets in both modes, at all four sizes and all three levels, and confirmed for every one that each listed word sits on the grid exactly once, that the slots read back from the grid match the list, that the logical solver reaches the printed answer exactly, that a Hard sheet cannot be finished within Medium's steps, that every surviving starter is needed, and that an independent exhaustive search with no technique ladder finds exactly one fit. Read more about how we make puzzle packs, or tell us about a sheet that misbehaves through the contact page.
Nothing here costs anything and there is no account. Puzzles are generated in your own browser rather than fetched from a server, so a word list you paste in never leaves your device, and the terms of use let teachers, tutors, clubs and families print and copy these sheets and their answer keys freely.