A detailed logo looks polished in a website header and becomes an unreadable blur in the browser tab. The favicon has a different job: it must remain recognisable in a very small space among other open pages.
MDN describes the favicon as the small icon associated with a website. Its tiny presentation is a reason to create a simplified version of a brand mark rather than shrinking every detail of the full logo.
Judge it at its working size
Preview a candidate at sixteen pixels as one useful stress test, as well as at the other sizes your implementation needs. Remove small lettering and decorative details that disappear. A strong shape with deliberate spacing usually communicates more than a miniature copy of a complex wordmark.
Check it against both light and dark browser interfaces. A transparent icon can lose an edge against one background even when it looks clear on the designer’s white canvas. Keep the relationship to the site’s identity without requiring every brand element to fit.
Verify the implementation separately
The HTML rel attribute documentation explains the icon relationship and how browsers can use type, size and media information when choosing among icons. Use valid assets and appropriate markup for the formats you provide.
Open the icon URL directly and inspect the page’s head and network requests. If an old icon remains visible, investigate caching instead of repeatedly uploading differently named copies without understanding which one the page references.
Test beyond the design file
Look at a real tab beside several unrelated sites and check bookmarks where relevant. Ask someone to identify the site from the small mark. The favicon succeeds when it provides a clear visual cue in use, not merely when the large source artwork looks attractive.