Medium impact · weight 7 · worth up to 2.2 points of the total score
Without a canonical, every URL variant that reaches this page (tracking parameters, trailing slash, uppercase path) can be indexed as a separate page, splitting the ranking signal between duplicates.
Add <link rel="canonical" href="..."> pointing at the absolute preferred URL of this page.
Check a page for this, and the other 41 checks at once
Images have alt text
Alt text is how a screen reader describes an image and how a search engine understands it. Missing alt attributes are an accessibility defect and lost image-search traffic at the same time.
Title length is in range
Below about 30 characters the strongest on-page signal is left half unused; past about 60 Google truncates the title in the results page and the tail is wasted.
Canonical points at this page
A canonical aimed somewhere else tells Google to index that other URL instead of this one. Done by accident, usually by copying a template, it removes the page from search while everything still looks fine on screen.
Document declares its language
The lang attribute tells screen readers which pronunciation rules to use and helps search engines serve the page to the right audience. Without it a screen reader may read English text with the wrong phonetics.
