Study: Claude Code 'Builds, Not Buys' — 2,430 Runs Show It Writes JWT+bcrypt From Scratch Before Reaching for Auth0

Amplifying·high signal

Amplifying ran Claude Code across 4 greenfield repos with 100 open-ended prompts, 20 tool categories, and three models (three runs each, 2,430 total); 'custom/DIY' was the single most common choice, topping 12 of 20 categories — it hand-rolls auth and feature flags rather than pulling a SaaS. But when it does adopt a tool it's decisive: GitHub Actions 94%, Stripe 91%, shadcn/ui 90%. For builders the lesson is that agents default to reinventing infrastructure, so if you want a specific library adopted you have to steer it explicitly in CLAUDE.md or the prompt.