How to Build a Zero-Dependency Web Tool with Vanilla JavaScript

There's a category of web app that doesn't need React. Or Vue. Or Svelte. Or a build step. Or node_modules . I'm talking about single-purpose developer tools: JSON formatters, color pickers, regex testers, cron builders. Tools that take input, transform it, and show output. No auth, no database, no API calls. For these, vanilla JavaScript isn't just "good enough" — it's better . Faster load times, zero maintenance burden, and deployment is literally copying files to a static host. Here's the architecture pattern I use, demonstrated with a real tool: CronMaker , a visual cron expression generator. The Architecture Every tool follows this structure: my-tool/ ├── index.html ← Structure + SEO ├── style.css ← Theming + responsive layout └── app.js ← All logic in an IIFE Three files. No package.json . No webpack.config.js . No .babelrc . No tsconfig.json . Nothing to update, nothing to break. Why an IIFE? All JavaScript goes inside an Immediately Invoked Function Expression: (() => { ' use s