The 404 page is usually the last thing anyone builds. Lately I do the opposite and make it one of the first three pages — home, article, 404. Two reasons.
Broken links become visible
Early development is when routes change constantly, which is exactly when links break most. A bare server-default 404 slides past your eyes; your own designed 404 makes you stop — “that one’s broken.” Building the error page turns out to be building an error detector.
The smallest design-system test
A 404 is the minimal page: a heading, a sentence, a link. That makes it the perfect canvas for verifying color tokens and typography. Cross-cutting styles — dark-mode switching, focus-ring visibility — were easiest to confirm on this one page first and then roll out to the article layout, with far less rework.
Takeaway
Before it is a page for visitors, the 404 works as an instrument for the builder during construction. For something that takes well under an hour, the value it pays back is out of proportion.