Configuring Astro

Customize how Astro works by adding an astro.config.mjs file in your project. This is a common file in Astro projects, and all official example templates and themes ship with one by default.

📚 Read Astro’s API configuration reference for a full overview of all supported configuration options.

A valid Astro config file exports its configuration using the default export, using the recommended defineConfig helper:

import { defineConfig } from 'astro/config'

export default defineConfig({
  // your configuration options here...
  // https://docs.astro.build/en/reference/configuration-reference/
})

Using defineConfig() is recommended for automatic type hints in your IDE, but it is also optional. An absolutely bare-minimum, valid configuration file would look like this:

// Example: Bare minimum, empty configuration file
export default {}

Astro supports several file formats for its JavaScript configuration file: astro.config.js, astro.config.mjs, astro.config.cjs and astro.config.ts. We recommend using .mjs in most cases or .ts if you want to write TypeScript in your config file.

TypeScript config file loading is handled using tsm and will respect your project tsconfig options.

Astro will automatically try to resolve a config file named astro.config.mjs inside project root. If no config file is found in your project root, Astro’s default options will be used.

# Example: Reads your configuration from ./astro.config.mjs
astro build

You can explicitly set a config file to use with the --config CLI flag. This CLI flag always resolves relative to the current working directory where you ran the astro CLI command.

# Example: Reads your configuration from this file
astro build --config my-config-file.js

Astro recommends using the defineConfig() helper in your configuration file. defineConfig() provides automatic IntelliSense in your IDE. Editors like VSCode are able to read Astro’s TypeScript type definitions and provide automatic jsdoc type hints, even if your configuration file isn’t written in TypeScript.

import { defineConfig } from 'astro/config'

export default defineConfig({
  // your configuration options here...
  // https://docs.astro.build/en/reference/configuration-reference/
})

You can also provide type definitions manually to VSCode, using this JSDoc notation:

export default /** @type {import('astro').AstroUserConfig} */ ({
  // your configuration options here...
  // https://docs.astro.build/en/reference/configuration-reference/
}

If you provide a relative path to root or the --root CLI flag, Astro will resolve it against the current working directory where you ran the astro CLI command.

import { defineConfig } from 'astro/config'

export default defineConfig({
  // Resolves to the "./foo" directory in your current working directory
  root: 'foo'
})

Astro will resolve all other relative file and directory strings as relative to the project root:

import { defineConfig } from 'astro/config'

export default defineConfig({
  // Resolves to the "./foo" directory in your current working directory
  root: 'foo',
  // Resolves to the "./foo/public" directory in your current working directory
  publicDir: 'public',
})

To reference a file or directory relative to the configuration file, use import.meta.url (unless you are writing a common.js astro.config.cjs file).

import { defineConfig } from 'astro/config'

export default defineConfig({
  // Resolves to the "./foo" directory, relative to this config file
  root: new URL("./foo", import.meta.url),
  // Resolves to the "./public" directory, relative to this config file
  publicDir: new URL("./public", import.meta.url),
})

For code that Astro processes, like imported JavaScript or CSS files, you can customise output filenames using entryFileNames, chunkFileNames, and assetFileNames in a vite.build.rollupOptions entry in your astro.config.* file.

import { defineConfig } from 'astro/config'

export default defineConfig({
  vite: {
    build: {
      rollupOptions: {
        output: {
          entryFileNames: 'entry.[hash].js',
          chunkFileNames: 'chunks/chunk.[hash].js',
          assetFileNames: 'assets/asset.[hash][extname]',
        },
      },
    },
  },
})

This can be helpful if you have scripts with names that might be impacted by ad blockers (e.g. ads.js or google-tag-manager.js).

Astro evaluates configuration files before it loads your other files. As such, you can’t use import.meta.env or access environment variables that were set in .env files.

You can use process.env in a configuration file to access other environment variables, like those set by the CLI.

📚 Read Astro’s API configuration reference for a full overview of all supported configuration options.