I run a free financial calculator site: 38 calculators, Next.js App Router, fully static, all math in the browser. When I audited it last month I found the problem you probably have in your own app too: reference numbers copy-pasted into too many places. The 2026 tax brackets lived in four calculators, three articles and a dozen FAQ answers. The default mortgage rate was typed into eight calculators, and every worked example computed from it went stale the week the rate moved. Worse, the FAQ an...