September 2026

.ipuz vs .puz: What's the Difference

If you've spent any time around crossword construction tools, you've run into both extensions and probably weren't told why there are two. Short version: they're solving the same problem a couple of decades apart, and one of them ran into limits the other was built to avoid.

.puz: old, binary, narrow — and everywhere

.puz is a compact binary format built for Across Lite, a desktop crossword player, back when "crossword file" basically meant "American-style grid with across and down clues." It's simple enough that it became the de facto standard for syndication and construction software, which is exactly why it's still the format you'll most often get handed a puzzle in — it isn't the newest option, it's the most universally supported one.

.ipuz: newer, JSON, built for more puzzle shapes

.ipuz is a human-readable, JSON-based format designed later, explicitly to handle what .puz's binary structure makes awkward: cryptics, variety grids, puzzles with non-standard shapes or rules beyond a simple across/down grid. Being JSON also makes it easier for new tools to read and write correctly, rather than needing to reverse engineer an old binary layout.

What this means if a file lands in your hands

Neither format tells you anything about content quality — a .puz file can be a beautifully constructed daily, and an .ipuz file can be a rough draft. The extension only tells you which structure the puzzle is stored in, and that an app needs to explicitly support that exact structure to open it at all. Which is the same problem covered in why a .puz file doesn't just open on its own — it applies just as much here.

Ultimate Crossword imports both formats directly, so which one you were handed shouldn't be your problem to solve.