Things a Solo Developer Learned While Building 40+ Financial Calculators with Next.js

I am building a web app called SorryClub, a collection of financial and productivity tools, all by myself. Currently, there are over 40 calculators, and I am continuously adding more. I would like to share how I technically structured it. Technology Stack Framework: Next.js 16 (App Router, React 19, Turbopack) DB: TiDB Serverless (MySQL compatible) Storage: Cloudflare R2 Hosting: Vercel Pro Auth: NextAuth 4 (Google, JWT) Payments: Lemon Squeezy AI: OpenAI GPT-4o (SEO Article Generation), Replicate Flux 1.1 Pro (Cover Image) Charts: Recharts Styling: Tailwind CSS 4 (Dark Mode Only) Managing 40 Tools in a Single Codebase All tools follow the same layout pattern. layout.js handles metadata, JSON-LD, FAQs, and related tools, while page.js is responsible for client-side logic. By establishing this pattern, we no longer need to worry about the structure when adding new tools. Tool metadata (title, icon, category, gradient color) is managed in the database. The frontend uses slug-based dynami