Cross-border tax engine for developers in Germany, Netherlands, Portugal, Spain and UK. - Income tax estimates 2025/2026, every rate cited to the statute - Residency check incl. UK Statutory Residence Test - 22 strategies: NL 30% ruling, PT IFICI, ES Beckham - rules in code Honest: UK test 8/17, Spanish foral partial, Dutch Box 3 outdated. That's why €29/year founding price, €99 when fixed. Founding members keep €29 forever. 977 tests. Cloudflare Workers, Hono, SolidJS, D1.