vite/references/core-config.md

---

name: vite-config description: Vite configuration patterns using vite.config.ts

---

Vite Configuration

Basic Setup

// vite.config.ts
import { defineConfig } from 'vite'

export default defineConfig({
  // config options
})

Vite auto-resolves vite.config.ts from project root. Supports ES modules syntax regardless of package.json type.

Conditional Config

Export a function to access command and mode:

export default defineConfig(({ command, mode, isSsrBuild, isPreview }) => {
  if (command === 'serve') {
    return { /* dev config */ }
  } else {
    return { /* build config */ }
  }
})

• command: 'serve' during dev, 'build' for production
• mode: 'development' or 'production' (or custom via --mode)

Async Config

export default defineConfig(async ({ command, mode }) => {
  const data = await fetchSomething()
  return { /* config */ }
})

Using Environment Variables in Config

.env files are loaded after config resolution. Use loadEnv to access them in config:

import { defineConfig, loadEnv } from 'vite'

export default defineConfig(({ mode }) => {
  // Load env files from cwd, include all vars (empty prefix)
  const env = loadEnv(mode, process.cwd(), '')

  return {
    define: {
      __APP_ENV__: JSON.stringify(env.APP_ENV),
    },
    server: {
      port: env.APP_PORT ? Number(env.APP_PORT) : 5173,
    },
  }
})

Key Config Options

input (top-level, Vite 8)

Declare entry points once at the top level. Acts as the default for build.rolldownOptions.input, build.lib.entry, build.ssr (when true), and optimizeDeps.entries. Useful when the app has no index.html entry.

export default defineConfig({
  input: 'src/main.ts',
  // or multi-page: { main: 'index.html', nested: 'nested/index.html' }
})

resolve.alias

export default defineConfig({
  resolve: {
    alias: {
      '@': '/src',
      '~': '/src',
    },
  },
})

The array form's customResolver was removed in Vite 8 — use a custom plugin with a resolveId hook and enforce: 'pre' instead.

define (Global Constants)

export default defineConfig({
  define: {
    __APP_VERSION__: JSON.stringify('1.0.0'),
    __API_URL__: 'window.__backend_api_url',
  },
})

Values must be JSON-serializable or single identifiers. Non-strings auto-wrapped with JSON.stringify.

plugins

import vue from '@vitejs/plugin-vue'

export default defineConfig({
  plugins: [vue()],
})

Plugins array is flattened; falsy values ignored.

server.proxy

export default defineConfig({
  server: {
    proxy: {
      '/api': {
        target: 'http://localhost:3000',
        changeOrigin: true,
        rewrite: (path) => path.replace(/^\/api/, ''),
      },
    },
  },
})

build.target

Default 'baseline-widely-available' → ['chrome111', 'edge111', 'firefox114', 'safari16.4', 'ios16.4'] (Vite 8, Baseline Widely Available as of 2026-01-01). Customize:

export default defineConfig({
  build: {
    target: 'esnext', // or 'es2020', ['chrome90', 'firefox88']
  },
})

To set the dev/transform target, use oxc.target (replaces esbuild.target); build.target takes precedence for builds.

tsconfig (Vite 8)

Force a specific tsconfig instead of Vite's per-file discovery. Discouraged — prefer placing tsconfig.json near the files it configures and using TS references.

export default defineConfig({ tsconfig: './tsconfig.app.json' })

devtools (Vite 8, experimental)

Enable Vite DevTools integration (requires @vitejs/devtools* packages). Cannot be set from a plugin config hook.

export default defineConfig({ devtools: { apply: 'serve' } })

TypeScript Intellisense

For plain JS config files:

/** @type {import('vite').UserConfig} */
export default {
  // ...
}

Or use satisfies:

import type { UserConfig } from 'vite'

export default {
  // ...
} satisfies UserConfig