Ask a US importer what duty they pay on a product and they will usually name one number: the rate in the tariff schedule. That number is almost never the whole bill.
The real cost is a stack. On top of the base duty rate, an import can carry Section 301 tariffs on Chinese goods, Section 232 duties on steel, aluminium and autos, and antidumping or countervailing duties that are set case by case, company by company — some of them well over 100%. A separate list under the Uyghur Forced Labor Prevention Act can get goods detained regardless of what you paid. None of these layers appear in the headline rate, and each one changes on its own schedule, in its own legal documents.
That is the problem I built HTS Radar for. It looks up the US tariff schedule — more than 29,000 codes — and shows the full stack that applies to a code: the base rate plus every additional layer, with the antidumping and countervailing cases attached to it (890 of them tracked so far). Importers can watch a code for free and get an email when one of its layers changes, because the expensive surprises in importing are never the rate you knew about. They are the layer that landed last month while nobody was watching that code.