Paste any address. This reads the page and reports which of the things it depends on do not answer behind the border — the fonts that hold your text invisible, the challenge widget that makes a form unsendable, the map that arrives as a grey box — and what is used instead. Nothing is stored and there is no sign-up.
Checks are limited to a few per visitor, and results are cached for five minutes.
One caveat, honestly: this reads what the page depends on, which is knowable from anywhere. It does not measure the border itself — reachability differs by province, by network and by week, and only a request made from inside can settle that.
Need a site that works on both sides of the border? That is the work we do, from inside the Greater Bay Area.