Down for Everyone or Just Me
downforeveryoneorjustme.com
Settles whether a site is actually down or only down for you
No sign-upClassic
Loading page
Inspect, test and troubleshoot anything with a URL.
downforeveryoneorjustme.com
Settles whether a site is actually down or only down for you
lookup.icann.org
The registry's own WHOIS record for a domain, with no upsell
ipinfo.io
Tells you an IP address's owner, network and approximate location
microlink.io
Turns any URL into a screenshot, a PDF or structured metadata
pagespeed.web.dev
Scores a page on real-user Core Web Vitals and lab measurements
ssllabs.com
Grades a site's TLS configuration from A+ down to F and says why
securityheaders.com
Grades the HTTP security headers a site sends and names the missing ones
uptimerobot.com
Watches your site around the clock and emails you when it stops answering
wave.webaim.org
Overlays accessibility errors directly on top of the page they affect
webpagetest.org
Loads your page from a chosen city and browser and films the result
whatsmydns.net
Checks a DNS record from dozens of resolvers around the world at once
By task
Archive
Kept on record so an old bookmark still leads to an answer. Each one names the site that does the job now.
Questions
There is no single answer, which is why this page lists 11 of them with their limits stated. If you want to avoid signing up entirely, 8 of these work with no account at all.
Every site in this category sends your input to its own server to do the work. That is fine for public material; for anything containing personal data, check the on-device collection instead.
Some already have. 3 entries in this category has been retired and moved to the Archive with a working successor, so an old bookmark still leads somewhere useful.