490+ Calculator Tools with Zero Hosting Cost — Architecture Deep Dive

I built a site with 490+ free calculator tools — BMI, loan payments, unit conversions, tax calculators — all statically generated with Next.js. Monthly hosting cost: $0. Here's the architecture behind keisan-tools. The Problem Japanese users search for specific calculators constantly. "BMI計算" (BMI calculator), "住宅ローン計算" (mortgage calculator), "年齢計算" (age calculator). Each query has moderate search volume with surprisingly low competition. Instead of building each tool by hand, I built a system that generates tools from configuration. Architecture Overview keisan-tools/ ├── data/ │ └── tools.json # 490+ tool definitions ├── app/ │ └── [category]/ │ └── [slug]/ │ └── page.tsx # Dynamic route template ├── lib/ │ ├── calculator.ts # Calculation engine │ └── tools.ts # Tool loader + search └── next.config.js # Static export config The Tool Definition Format Each calculator is a JSON object: { "slug": "bmi-calculator", "category": "health", "title": "BMI計算ツール", "description": "身長と体重からBMIを計算"