Vite error 'Failed to resolve import "..." from "src/...". Does the file exist?' (or Rollup 'failed to resolve import') with a path alias like '@/' that is not working

Cause: Vite does not read the paths mapping in tsconfig.json for resolution. An alias such as '@/components/Button' only works if it is also declared in Vite's resolve.alias (or provided by a plugin that reads tsconfig paths). Other common causes are a misspelled path, a package that is not installed, or an import that omits an extension Vite does not try. Fix (best first): 1. Declare the alias in vite.config.js/ts. The Vite docs say to use absolute file system paths for alias targets, since relative values are used as-is: import { fileURLToPath, URL } from 'node:url' export default defineConfig({ resolve: { alias: { '@': fileURLToPath(new URL('./src', import.meta.url)) } } }) 2. Keep tsconfig.json "paths" in sync with it, so the editor and type checker understand the same alias (Vite does not use it, TypeScript does). 3. Alias rules are applied in the order defined; with the array form ({ find, replacement }) put the most specific rule first, and a RegExp find can use $1 in the replacement. 4. If the import is a package, install it (npm install <pkg>) and restart the dev server. After npm link or linking local packages, Vite's dependency cache is not invalidated, so run vite --force once. 5. Check resolve.extensions. The default is ['.mjs', '.js', '.mts', '.ts', '.jsx', '.tsx', '.json']; importing a file with another extension (such as .vue) needs the extension written out, and the docs advise against adding custom types to the list. 6. If the config file itself is reported as failing to resolve an ESM-only package, make the config ESM by adding "type": "module" to the nearest package.json or renaming it to vite.config.mjs/.mts. Verify: restart vite, confirm the page loads without the overlay error, and run the build once (vite build) because dev and build resolve through the same alias list. Sources: https://vite.dev/config/shared-options.html https://vite.dev/guide/troubleshooting