If want to check an individual site, if is free. But if you want to set up monitors across a swath of sites and technologies, they have plans priced from $295-9

If want to check an individual site, if is free. But if you want to set up monitors across a swath of sites and technologies, they have plans priced from $295-995/mo. https://builtwith.com/plans https://builtwith.com/plans