example.com and www.example.com look like the same website to a person. They are still two host
names. Each needs a DNS answer, and each can return its own HTTP response.
A clean setup chooses one home. The other host sends a visitor there in one redirect. IndieWWW checks that exact path. Enter a domain and it asks Cloudflare DNS over HTTPS for the public records of the apex and www hosts. It then makes one direct HTTPS request to each host with redirects disabled, so the first response and its Location header stay visible.
The result does not prefer apex over www. Either is a valid choice. A permanent one-hop redirect to the serving host passes. A temporary redirect or two separately serving hosts gets a warning. A missing host, a loop, or a counterpart that never reaches the chosen host fails.
This is one configuration signal. Google documents redirects as a strong canonical signal, but a passing IndieWWW result is not an SEO score and does not promise indexing. The check also comes from one place at one time. DNS propagation, caches, firewalls, and bot protections can make a visitor elsewhere receive something different.
The core stays free. There is no account, card, premium plan, or public list of checked domains. IndieWWW stores no lookup history and loads no analytics or third-party script in the page.