Constructor Resources

Interested in building your own crossword puzzles? Here’s a list of mostly free resources for your new endeavor.

General construction guidelines

Crosswords:

should have black square symmetry, which typically comes in the form of 180-degree rotational symmetry.
should have all-over interlock.
must not have unchecked squares (i.e., all letters must be found in both Across and Down answers).
should have answers with a minimum length of 3 letters.
must use black squares in moderation.
must not repeat words.
should symmetrically place long theme answers.

(The tools below can help with many of these.)

Fill and clues should:

[Combined from Cruciverb and the New York Times guidelines]

Choose a size. The standard is 15x15, but I’ve seen squares of all sizes and even some rectangles, or a heart once!
Decide on a theme, if any (themeless are a-okay), and come up with those clue and answer pairings first.
Build the grid with the black squares amenable to your theme words and in accordance with the guidelines above. These templates can get you started otherwise.
Fill in the longer answers first and build fill around them.
Include rarer letters earlier in the grid filling process. They’ll be harder to fit in later. Generally, they improve the quality of the puzzle.

In order not to repeat words, you can parse answers creatively. For example, O-N-E can be ‘one’ like the number or ‘on E’ like a gas gauge. So in my opinion, it’s not repeating if you use ‘PLUS ONE’ and ‘ON E’ if they’re clued appropriately.
If you’re running into issues filling your grid around themed answers, try swapping answers of the same length to see if the new placement works better.
E, S, D, T, and N are the most common final letters of words. You might have better luck using them as you move to the right and the bottom of the puzzle. BUT it’s probably more interesting if you use some crazy letters instead! (source)
When building your grid, you can’t put a black square two or three spaces from any edge unless you chain them to the edge with other black squares (or unless you have a theme that compensates). Otherwise, you won’t meet the 3-letter minimum length.