A 404 “page not found” error shows a problem happened when someone tried to reach a web page. Webmasters should reach for the opportunity to make those occasions work for them, not against them.

Searchers despise the 404 error page, especially when it comes from clicking what looks like a relevant link in a list of search results. Too often, these 404s come up as an ineffective default page in the browser, leaving the visitor no other real choice but to hit the Back button and try again.

One may end up leery of future results from that domain, a brutal blow to a webmaster who may not realize without carefully checking the log files that people are hitting and missing something on their sites.

The biggest search engine, Google, prefers not to see this. It not only diminishes the value of the destination sites returning a 404 error, but the quality of its search results. A poorly configured delivery of 404 results may keep an otherwise dead page alive in Google’s index, to be found again and again.

It’s basic stuff, as commenters on the first of a short series of posts at the Google Webmaster Central blog noted. Is someone really a webmaster if they don’t know to return a 404 error when a page is not found?

Not all 404s are created equal, as Maile Ohye said at the blog today. A 404 could be a soft error or a hard one.

The soft 404 response is the undesirable result. This happens when someone tries to visit a nonexistent URL on a site. Instead of an error page, the website returns a 200 response code and sends the request to the site’s homepage.

On the user’s side, the person who encountered this probably questioned the sanity of the webmaster on the other end who let this useless result happen. It’s not a good way to earn repeat visits.

Give the visitor a real 404 page not found result, Ohye said. It’s a clear indication both to human and automated visitors about the status of the page.

Google plans to make a week of the 404, and we’ve got a pretty good idea of where they are going judging by Ohye’s comment about sending a helpful “Not found” message to the viewer. Webmasters have the ability to deliver any kind of page in response to a 404 situation.

Such a page could let the visitor know that, while the page they wanted isn’t there, other pages on the site may be exactly what they need. Weather.com demonstrates this well: this link brings up two types of content.