Crossword autofill is a solver that fills the empty squares of a grid with real words so every crossing works. It treats the grid as a constraint problem: pick the slot with the fewest options, try the best-scoring word, and back up when a crossing has no possible word. Results depend mostly on how much of the grid you've already filled and how good your word list is.
How does crossword autofill work?
Every entry in a grid is a slot (a run of white squares, across or down). Each square belongs to two slots, so a letter you place in one slot constrains another. Autofill searches for a set of words that satisfies all those overlaps at once. That is a constraint satisfaction problem, and most fillers use the same core ideas:
- Pick the most constrained slot first. Count how many words in the list still fit each unfinished slot's pattern (such as
S..RK) and work on the one with the fewest. Fewer options means a mistake shows up sooner. This is the "minimum remaining values" heuristic. - Try the best words first. Candidates are ranked by score, so the first fill found tends to be the nicest one.
- Forward check. After placing a word, look at every crossing slot. If any crossing now has zero possible words, reject the word immediately instead of exploring a dead end.
- Backtrack. If a slot runs out of options, undo the last choice and try the next word.
- Don't repeat words. A word already used in the grid is excluded.
- Stop on a budget. Without a limit, the search can run for a very long time, so the solver gives up after a set number of attempts.
Gridsmith's solver follows this recipe, and it runs in a background Web Worker so the page stays responsive.
Why are blank grids so hard to autofill?
A 15×15 grid with only black squares placed has many long slots and nothing to anchor them. Early choices have huge consequences, and a bad corner can be impossible to fix until the search has tried an enormous number of combinations. Backtracking has to undo many placements to repair it. The more letters already in place, the smaller the search.
So treat a full-grid fill from scratch as the hardest case. It may be slow or hit the attempt limit, and that's normal. It is a known limit of simple backtracking solvers, not a sign you did something wrong.
What settings give the best autofill results?
Seed the grid first
Place your theme entries before running autofill. They give the solver fixed letters on both axes and cut the search dramatically. See crossword theme ideas for building those entries.
Lock the entries you love
Autofill never changes letters already in the grid; it only fills blanks, using what's there as constraints. Type the answers you want (a great long entry in a corner, say) and the solver will build around them.
Fill the hard corners first
Corners with 3-letter stacks, or crossings of long entries, are where the solver most often dies. Fill them yourself or autofill just those slots, then fill the rest. If a region won't fill, change a black square: moving one block often fixes a corner that no word list can. Basic constraints on blocks are in crossword grid rules.
Use a better word list
The same grid gives dramatically different results with a scored list. See crossword word lists for options.
Fill in chunks
Fill one region, review it, and fix anything ugly before moving on. A full run in one go gives you whatever the solver found first, which may include entries you dislike.
Always review the result
Autofill doesn't know what's fresh, what's overused, or whether three Naticks cross. It only knows scores and fit. Read every entry before you clue it.
How do I use autofill in Gridsmith?
- Build the grid and place theme entries; symmetry is applied automatically, per how to make a crossword puzzle.
- For a single slot: select it, open Tools, and choose Autofill word. This fills only the active slot, consistent with its crossings.
- For everything left: choose Autofill puzzle. Gridsmith searches within a budget of 500,000 attempts (200,000 for a single word) and tells you if it solved, ran out of options, or was cancelled. You can cancel a running fill.
- If it fails, add more letters or move a block and run it again.
- For manual control, use the ranked suggestions for the active slot, which are consistent with crossing letters.
- Import a scored list under Tools → Import words… for better quality.
Gridsmith doesn't promise an instant full-grid fill. Large blank grids can take a while or fail, and the approach above is the way to avoid that.
Frequently asked questions
What is crossword autofill?
It's software that completes a partly filled crossword grid with valid words, making sure every crossing letter agrees. It uses a word list to know which words are allowed.
Can autofill fill an entire blank crossword?
Sometimes, but a blank 15×15 is the hardest case and may be slow or fail. Seeding theme entries and filling in sections works far better.
Why does autofill give me weird or obscure words?
Usually because the word list is unscored or the pattern has few options. A scored list and a revised block layout both help.
Does autofill change letters I've already typed?
No. In Gridsmith, existing letters are treated as fixed and only blank squares are filled.
Is autofill cheating?
Most constructors use fill tools. The creative parts, theme, grid design and clues, are still yours, and you should review every entry the tool chooses.