Major crossword variants
These are common crossword variants that vary more from a regular crossword than just an unusual grid shape or unusual clues; these crossword variants may be based on different solving principles and require a different solving skill set.
Published under various trade names (including Code Breakers, Code Crackers, and Kaidoku), and not to be confused with cryptic crosswords (ciphertext puzzles are commonly known as cryptograms), a cipher crossword replaces the clues for each entry with clues for each white cell of the grid - a number integer from 1 to 26 inclusive is printed in the corner of each. The objective, as any other crossword, is to determine the proper letter for each cell; in a cipher crossword, the 26 numbers serve as a cipher for those letters: cells that share matching numbers are filled with matching letters, and no two numbers stand for the same letter. All resultant entries must be valid words. Usually, at least one number's letter is given at the outset. English-language cipher crosswords are nearly always pangrammatic (all letters of the alphabet appear in the solution). As these puzzles are closer to codes than quizzes, they require a different skillset; many basic cryptographic techniques, such as determining likely vowels, are key to solving these. Given their pangrammaticity, a frequent start point is locating where 'Q' and 'U' must appear.
In a diagramless crossword, often called a diagramless for short or, in the UK, a skeleton crossword or carte blanche, the grid offers overall dimensions, but the locations of most of the clue numbers and black squares are unspecified. A solver must deduce not only the answers to individual clues, but how to fit together partially built-up clumps of answers into larger clumps with properly-set black squares. Some of these puzzles follow the traditional symmetry rule, others have left-right mirror symmetry, and others have greater levels of symmetry or outlines suggesting other shapes. If the symmetry of the grid is given, the solver can use it to his/her advantage.
A variation is the Blankout puzzle in the Daily Mail Weekend magazine. The clues are not individually numbered, but given in terms of the rows and columns of the grid, which has rectangular symmetry. The list of clues gives hints of the locations of some of the black squares even before one starts solving them, e.g. there must be a black square where a row having no clues intersects a column having no clues.
A fill-in crossword (also known as crusadex or cruzadex) features a grid and the full list of words to be entered in that grid, but does not give explicit clues for where each word goes. The challenge is figuring out how to integrate the list of words together within the grid so that all intersections of words are valid. Fill-in crosswords may often have longer word length than regular crosswords to make the crossword easier to solve, and symmetry is often disregarded. Fitting together several long words is easier than fitting together several short words because there are fewer possibilities for how the long words intersect together.
A crossnumber (also known as a cross-figure) is the numerical analogy of a crossword, in which the solutions to the clues are numbers instead of words. Clues are usually arithmetical expressions, but can also be general knowledge clues to which the answer is a number or year. There are also numerical fill-in crosswords.
The Daily Mail Weekend magazine used to feature crossnumbers under the misnomer Number Word. This kind of puzzle should not be confused with a different puzzle that the Daily Mail refers to as Cross Number.