Build a calculator web app and refactor it with Devin
A Scott Logic developer built a calculators web app with Devin, then had it plan a refactor of the bloated codebase, and feeding the plan back in chunks cut project size by about 60%.
Done withDevin
- What they did
- James Camilleri gave Devin a carbon-emissions spreadsheet and a connected repo. His first Electron attempt failed, so he restarted with TypeScript/React, starting with the calculation models and then the UI. Devin planned, branched, built and raised PRs for him to review. After a few calculators the code was repetitive, so he had Devin analyse it and write a refactoring plan, which he fed back in chunks.
- How it went
- The refactor cut project size by about 60%. The app took just over a week. Camilleri couldn't read all the generated code, so he relied on tests and focused review of key logic.
- Worth knowing
- The build used about 155 ACUs, roughly $350, and the account needed several top-ups. Start new sessions regularly to avoid context rot.
Try it yourself with Devin
Build a small web app in [framework, e.g. React] that provides [type of calculators, e.g. mortgage, tip, unit conversion], with a clean layout and basic tests. When it works, review the codebase and write a step-by-step refactor plan that removes duplication and unused code, split into small chunks I can approve one at a time. Pause after presenting the plan and wait for my go-ahead before changing any code, then finish when the tests pass and you've reported how much smaller the project got.
Want help getting this working? Join the Vibe Coding Academy ↗ Run by Alex Finn, who also runs this site.
Source: blog.scottlogic.com · Oct 20, 2025
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