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The adapter generates a config.json file in the .next/output directory. This file configures how Vercel serves your Next.js application.
This file is automatically generated during the build process. You typically don’t need to modify it directly.

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Configuration structure

The generated configuration follows the Vercel Build Output API v3 specification.

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Root configuration

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version
number
required
Build Output API version. Always set to 3.
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routes
Route[]
Array of routing rules that define how requests are handled. Routes are processed in order.
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images
ImagesConfig
Image optimization configuration derived from Next.js image settings.
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wildcard
WildcardConfig
Wildcard domain configuration for i18n. Maps domains to their default locale paths.
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overrides
OverridesConfig
required
File override configuration for static assets. Maps paths to custom content types or file paths.
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cache
string[]
Array of paths or patterns to cache.

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Example configuration

config.json
{
  "version": 3,
  "routes": [
    { "handle": "filesystem" },
    {
      "src": "^/api/(.*)$",
      "dest": "/api/$1"
    }
  ],
  "images": {
    "sizes": [640, 750, 828, 1080, 1200, 1920, 2048, 3840],
    "domains": ["images.example.com"],
    "remotePatterns": [],
    "formats": ["image/avif", "image/webp"]
  },
  "overrides": {}
}

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Images configuration

The images object configures Vercel’s image optimization service.
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images.sizes
number[]
required
Array of image widths to generate. Combines Next.js imageSizes and deviceSizes.
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images.domains
string[]
required
Array of allowed external domains for image optimization.
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images.remotePatterns
RemotePattern[]
Array of remote URL patterns for image optimization with fine-grained control.Each pattern includes:
  • protocol: 'http' or 'https' (optional)
  • hostname: Domain pattern as a regex source string
  • port: Port number (optional)
  • pathname: Path pattern as a regex source string (optional)
  • search: Query string pattern (optional)
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images.localPatterns
LocalPattern[]
Array of local file patterns for image optimization.Each pattern includes:
  • pathname: Path pattern as a regex source string (optional)
  • search: Query string pattern (optional)
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images.qualities
number[]
Array of quality values for image optimization (1-100).
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images.minimumCacheTTL
number
Minimum cache TTL in seconds for optimized images.
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images.formats
ImageFormat[]
Supported image formats: 'image/avif' or 'image/webp'
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images.dangerouslyAllowSVG
boolean
Whether to allow SVG image optimization.
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images.contentSecurityPolicy
string
Content Security Policy for image responses.
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images.contentDispositionType
string
Content-Disposition type for image responses.

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Example images configuration

{
  "images": {
    "sizes": [16, 32, 48, 64, 96, 128, 256, 384, 640, 750, 828, 1080],
    "domains": ["cdn.example.com"],
    "remotePatterns": [
      {
        "protocol": "https",
        "hostname": "images\\.example\\.com",
        "pathname": "\\/uploads\\/.*"
      }
    ],
    "qualities": [75, 90, 100],
    "minimumCacheTTL": 60,
    "formats": ["image/avif", "image/webp"],
    "dangerouslyAllowSVG": false
  }
}
The hostname and pathname in remotePatterns are stored as regex source strings, not plain patterns. The adapter automatically converts Next.js patterns using picomatch.

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Wildcard configuration

The wildcard array configures domain-specific i18n routing.
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wildcard[].domain
string
required
Domain name for this wildcard configuration.
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wildcard[].value
string
required
Path prefix for this domain. Empty string for domains using the default locale.

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Example wildcard configuration

{
  "wildcard": [
    {
      "domain": "example.com",
      "value": ""
    },
    {
      "domain": "example.fr",
      "value": "/fr"
    }
  ]
}
This configuration routes requests to example.com without a locale prefix (default locale) and requests to example.fr with the /fr prefix.

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Overrides configuration

The overrides object maps file paths to custom configurations.
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overrides[path].path
string
Custom file path to serve instead of the default.
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overrides[path].contentType
string
Custom content type for the file.

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Example overrides configuration

{
  "overrides": {
    "/_next/static/css/custom.css": {
      "contentType": "text/css; charset=utf-8"
    }
  }
}

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Routes configuration

The routes array defines routing rules processed in order. Routes are generated based on your Next.js configuration, including redirects, rewrites, headers, and dynamic routes.

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Route types

The adapter generates several types of routes:
  • Handle routes: Special routing handlers like filesystem, resource, miss, rewrite, hit, error
  • Redirect routes: Include status and dest fields
  • Rewrite routes: Include dest field for internal rewrites
  • Header routes: Include headers field to set response headers
  • Conditional routes: Include has or missing fields for conditional matching

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Example routes

{
  "routes": [
    {
      "src": "^/old-path$",
      "dest": "/new-path",
      "status": 308
    },
    { "handle": "filesystem" },
    {
      "src": "^/api/(.*)$",
      "dest": "/api/$1",
      "check": true
    },
    { "handle": "error" }
  ]
}
The routes array is automatically generated from your Next.js configuration, including i18n settings, redirects, rewrites, headers, and dynamic routes. See the adapter source code at packages/adapter/src/index.ts:261-936 for the complete routing logic.

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Build output location

The adapter generates the configuration file at: 
.next/output/config.json
This directory also contains:
  • Function bundles in .next/output/functions/
  • Static files in .next/output/static/
  • Prerender manifests in .next/output/prerender/

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