Low impact · weight 3 · worth up to 0.8 points of the total score
An error logged while the page loads usually means a script stopped halfway: a menu that does not open, a form that does not submit, an analytics tag that records nothing. Visitors never see the message, only the broken behaviour.
Open the browser console on the page and fix the first error listed; later ones are often caused by it. A failing third-party tag can be removed or loaded with async.
Check a page for this, and the other 70 checks at once
No deprecated presentational tags
Tags like <center> and <font> were removed from the standard. Browsers still honour them today, but they mix styling into the markup and no longer respond to CSS the way the rest of the page does.
Page declares a favicon
The favicon is how a user finds this tab among twenty others and how the site appears in bookmarks and history. Without a declared one the browser requests /favicon.ico and usually gets a 404.
Styling lives in stylesheets, not attributes
Inline style attributes cannot be cached, overridden by a stylesheet, or covered by a Content Security Policy that forbids inline styles. In quantity they also bloat every HTML response.
Links that open a new tab use rel=noopener
A page opened with target="_blank" can reach back to the page that opened it and send it elsewhere. Current browsers assume noopener, but older ones and some in-app browsers do not, and saying it costs nothing.
