About the URL Slug Generator
A slug is the part of the URL that describes the page. Good ones are short, lowercase, hyphenated and readable out loud. Bad ones contain dates that age, numbers that mean nothing and stop words that add length without information.
Use hyphens rather than underscores. Search engines treat a hyphen as a word separator and an underscore as a joiner, so two_words can be read as a single token while two-words is read as two.
The most important rule is about changing them. Once a URL has been live and has links pointing at it, editing the slug throws that away unless you add a 301 from the old address. If you are going to change it, change it early, and redirect it properly when you do.
Common questions
Should I use hyphens or underscores?
Hyphens. Search engines read a hyphen as a word separator and an underscore as a joiner, so two-words is read as two words while two_words can be read as one token.
Is it safe to change a URL slug after the page has been live for a while?
Only with a 301 redirect from the old URL to the new one. Without it, any existing links and search rankings pointing at the old address are lost.
Should slugs include stop words like 'the' and 'and'?
Generally no — they add length without adding information. The generator strips them by default, though you can keep them if a specific phrase reads oddly without one.