I like how fast btc2fiat.me loads and that it has no trackers.
One improvement / addition suggestion, would be a completely static version, that lets you pass a URL parameter.
It would be even more lightweight and require no JavaScript.
Let's say I go to
https://btc2fiat.me/?btc=0.5, it would display a static version of the current webpage, with the amount set to 0.5BTC.
And
https://btc2fiat.me/?usd=50.0 would display the exchange rate for 50USD.
My motivation for this idea is:
https://plaintextsports.com/Hey, yeah the plan is to be able to use non-JS but for calculators where you expect immediate input that becomes tricky. I still think it would be cool to have that support. In fact plaintextsports.com is using JS for its toggle light-dark mode.