The SEO crawler that won't stay quiet about your site's problems.
A browser shows you the last page and nothing about the three requests it took to get there. This shows every hop.
It asks for the address and does not follow the jump automatically: it asks, writes down the answer, works out where it is being sent and asks again. That is how the whole chain becomes visible rather than only where it ends, which is all a browser ever shows.
How many hops. Each one is a round trip your visitor pays for. Google gives up at around the fifth, so a long chain is ranking left on the floor.
A 302 doing a 301's job. The finding that surprises people most. A 302 tells a search engine to keep indexing the old address and treat the new one as a stand-in, so a site that moved years ago on a 302 is, as far as Google is concerned, still where it left.
A step back down to HTTP. A browser shows the padlock on the page it ends on and says nothing about a hop in the middle where the request travelled in the clear. This is the genuinely invisible one.
A meta refresh at the end. It never appears in a Location header, so a checker that only reads headers calls the chain finished at a page the reader does not stay on. This one follows it.
Loops and broken endings. A chain that comes back on itself is a page nobody can reach; one that ends on a 404 is worse than not redirecting at all.
One permanent hop is fine. Redirecting HTTP to HTTPS, or the bare domain to the www one, is the right thing to do, and this page says so rather than scolding you for it.