I use "what is my IP" sites maybe once a month. Every time I end up on something covered in ads, calling three different tracking APIs, and showing me results I don't fully understand. So I spent a weekend building whatsmy.fyi.
The thing I didn't expect: you don't need an IP geolocation API at all if you're on Cloudflare Workers. Every request comes with a cf object that already has your city, country, ISP, TLS version, HTTP protocol, and RTT. Free. Zero latency.
The part I enjoyed most was the WebRTC leak test. It checks whether your browser is exposing your real IP through RTCPeerConnection even when you're on a VPN. I ran it on my own setup. It was leaking.
Zero logs. Zero storage. Just your data, shown to you.
