Summary: Block Fill (a cut-up crossword) hands you a filled crossword that has been sliced into small square blocks and shuffled. You rebuild the grid by fitting every block back into place, starting from a few letters already printed on the board. This guide explains the goal, the rules that make it solvable, and how to play it online.
Overview
Start with a completed crossword — a grid where every white square holds a letter and every letter is part of both an across word and a down word. Cut that grid into equal square blocks (3×3 is the usual size), shuffle the blocks into a bank, and print the empty grid beside them. Your job is to put every block back so the crossword is whole again.
You are not answering clues. It’s a jigsaw with rules: the letters where blocks meet must spell real words straight across the join, so the crossword reassembles in one way and the printed hints tell you where to begin.
The Goal
Place every block from the bank back onto the grid so the whole board reads as one finished crossword — every across word and every down word complete, no gaps, and nothing left over but the decoys. Each block goes in one place, in the orientation it was cut.
The Rules That Make It Solvable
- The finished grid is a real crossword. Every white cell belongs to a horizontal word and a vertical word, and no word repeats. That interlock is what makes each block’s home unambiguous — the surrounding words rarely leave a second place a piece could sit.
- Blocks tile the grid edge to edge. The blocks butt together with no overlaps and no gaps, and the bank holds exactly enough real blocks to cover every cell (plus any decoys).
- Blocks are square and never rotated. Every block is the same size and goes back the same way up — you slide a block into place, you never flip or turn it.
- Every block is unique. No two blocks in the bank are identical — not even a decoy. So no block can stand in for another: once you find a block’s home, that block is the only piece that fits there.
- Anchor hints are scattered, not clustered. A few letters are pre-printed on the empty grid (shown highlighted). They are spread across different blocks on purpose, so you get a foothold in several regions and deduce the rest from the seams — the lines where two blocks touch.
- Decoys (optional) belong nowhere. Some puzzles add extra blocks that are not part of the solution. Each decoy is drawn to look different from every real block. You still confirm it by reasoning: a block that fits nowhere is a decoy, and so is anything left in the bank once the grid is full.
How to Start Solving
- Anchor first. Each printed hint letter fixes a letter at that exact cell, so only a block carrying that letter in that position can cover it. Find the block that matches each hint.
- Match the seams. A seam is where two blocks touch. Where a placed block leaves a half-finished word running off its edge, find the block whose matching edge continues that word into real letters.
- Read the black squares. Each block carries its own pattern of black (blocked) cells. Scan the empty grid for the one spot whose blocked cells match that shape — a block with an unusual black pattern often has only one place it can sit.
- Build outward from what’s fixed. Each block you lock in fixes the seam letters for its empty neighbours, shrinking which remaining blocks can fit there. Place the certain ones first and let them narrow the rest.
- Leftovers are decoys. When the grid is full, any block still in the bank is a decoy. Stuck with a block that fits nowhere? Set it aside as a decoy and keep going.
Words or Numbers
Block Fill comes in two flavours that play by the identical rules:
- Block Fill (words) — the cells hold letters that form an interlocking crossword.
- Number Block Fill — the cells hold digits instead of letters, so there is no vocabulary to know: you reassemble the grid purely from the block shapes, the black squares, and the hints. It is a separate puzzle for solvers who prefer numbers over words — see How Number Block Fill Puzzles Work.
Play It Online
Block Fill plays right in the browser. The scrambled blocks sit in a tray; drag a block onto the grid to place it, drag it somewhere else to move it, and press Verify to check whether every block is home. Decoys never fit, so a solved board uses each real block once and leaves the decoys in the tray. The general player controls (checking your answer, the timer, working through a set) are covered once in How to Play Puzzles Online.
Outcome
You now know the goal, the rules that make a Block Fill solvable — real crossword interlock, blocks that tile edge to edge, unique un-rotated pieces, scattered anchors, and decoys that fit nowhere — where to start solving, and the words-versus-numbers choice. Ready to make your own? See How to Create Block Fill Puzzles in Puzzle Maker Pro.
FAQ
Do I need to know the answers to crossword clues?
No — there are no clues. The words are already filled in on the blocks. Block Fill is about placing the cut pieces so the crossword reassembles.
Could two different blocks fit the same spot?
No. Every block in the bank is unique, so no block can substitute for another — once you find where a block goes, no other piece could have gone there.
What are the extra blocks that fit nowhere?
Those are decoys — optional blocks that belong nowhere in the solution, added to make the bank harder to sort. A puzzle can have none, a few, or many.
Are the blocks ever rotated or flipped?
No. Every block is placed in the same orientation it was cut. You only slide a block into position.
What is the difference between Block Fill and Number Block Fill?
Only the cell content: Block Fill uses letters that spell interlocking words; Number Block Fill uses digits and needs no dictionary. The reassembly logic is identical.