An ECW file contains a crossword created by EclipseCrossword, a program used to generate crossword puzzles. It contains a crossword puzzle, which includes each word with its clue and whether it is down or across. ECW files also include the title, author, copyright, and letter width and height of the puzzle.

You can open ECW files in EclipseCrossword. However, the program is only available for Windows. If you come across an ECW file in macOS you can open the ECW file with a text editor since the file is stored in plain text. You can print crosswords stored in ECW files and save them as webpages in EclipseCrossword. You can also publish ECW puzzles as .RTF, .WMF, .EPS files.