Build Output Configuration
Learn about the Build Output Configuration file, which is used to configure the behavior of a Deployment..vercel/output/config.json
Schema (as TypeScript):
type Config = {
version: 3;
routes?: Route[];
images?: ImagesConfig;
wildcard?: WildcardConfig;
overrides?: OverrideConfig;
cache?: string[];
crons?: CronsConfig;
};Config Types:
The config.json file contains configuration information and metadata for a Deployment.
The individual properties are described in greater detail in the sub-sections below.
At a minimum, a config.json file with a "version" property is required.
.vercel/output/config.json
The version property indicates which version of the Build Output API has been implemented.
The version described in this document is version 3.
"version": 3.vercel/output/config.json
The routes property describes the routing rules that will be applied to the Deployment. It uses the same syntax as the routes property of the vercel.json file.
Routes may be used to point certain URL paths to others on your Deployment, attach response headers to paths, and various other routing-related use-cases.
type Route = Source | Handler;type Source = {
src: string;
dest?: string;
headers?: Record<string, string>;
methods?: string[];
continue?: boolean;
caseSensitive?: boolean;
check?: boolean;
status?: number;
has?: Array<HostHasField | HeaderHasField | CookieHasField | QueryHasField>;
missing?: Array<
HostHasField | HeaderHasField | CookieHasField | QueryHasField
>;
locale?: Locale;
middlewareRawSrc?: string[];
middlewarePath?: string;
};| Key | Type | Required | Description |
|---|---|---|---|
| src | String | Yes | A PCRE-compatible regular expression that matches each incoming pathname (excluding querystring). |
| dest | String | No | A destination pathname or full URL, including querystring, with the ability to embed capture groups as $1, $2, or named capture value $name. |
| headers | Map | No | A set of headers to apply for responses. |
| methods | String[] | No | A set of HTTP method types. If no method is provided, requests with any HTTP method will be a candidate for the route. |
| continue | Boolean | No | A boolean to change matching behavior. If true, routing will continue even when the src is matched. |
| caseSensitive | Boolean | No | Specifies whether or not the route src should match with case sensitivity. |
| check | Boolean | No | If true, the route triggers handle: 'filesystem' and handle: 'rewrite' |
| status | Number | No | A status code to respond with. Can be used in tandem with Location: header to implement redirects. |
| has | Array<HostHasField | HeaderHasField | CookieHasField | QueryHasField> | No | Conditions of the HTTP request that must exist to apply the route. |
| missing | Array<HostHasField | HeaderHasField | CookieHasField | QueryHasField> | No | Conditions of the HTTP request that must NOT exist to match the route. |
| locale | Locale | No | Conditions of the Locale of the requester that will redirect the browser to different routes. |
| middlewareRawSrc | String[] | No | A list containing the original routes used to generate the middlewarePath. |
| middlewarePath | String | No | Path to an Edge Runtime function that should be invoked as middleware. |
Source route: Locale
type Locale = {
redirect?: Record<string, string>;
cookie?: string;
};| Key | Type | Required | Description |
|---|---|---|---|
| redirect | Map | Yes | An object of keys that represent locales to check for (en, fr, etc.) that map to routes to redirect to (/, /fr, etc.). |
| cookie | String | No | Cookie name that can override the Accept-Language header for determing the current locale. |
Source route: HostHasField
type HostHasField = {
type: 'host';
value: string;
};| Key | Type | Required | Description |
|---|---|---|---|
| type | "host" | Yes | Determines the HasField type. |
| value | String | Yes | Host name that must match the request URL's host to cause this route to match. |
Source route: HeaderHasField
type HeaderHasField = {
type: 'header';
key: string;
value?: string;
};| Key | Type | Required | Description |
|---|---|---|---|
| type | "header" | Yes | Determines the HasField type. |
| key | String | Yes | Header name that must exist on the request for this route to match. |
| value | String | No | Header value (or regex) that must match for this route to match. |
Source route: CookieHasField
type CookieHasField = {
type: 'cookie';
key: string;
value?: string;
};| Key | Type | Required | Description |
|---|---|---|---|
| type | "cookie" | Yes | Determines the HasField type. |
| key | String | Yes | Cookie name that must exist on the request for this route to match. |
| value | String | No | Cookie value (or regex) that must match for this route to match. |
Source route: QueryHasField
type QueryHasField = {
type: 'query';
key: string;
value?: string;
};| Key | Type | Required | Description |
|---|---|---|---|
| type | "query" | Yes | Determines the HasField type. |
| key | String | Yes | Querystring key to look for. |
| value | String | No | Querystring value (or regex) that must match for this route to match. |
The routing system has multiple phases. The handle value indicates the start of a phase. All following routes are only checked in that phase.
type HandleValue =
| 'rewrite'
| 'filesystem' // check matches after the filesystem misses
| 'resource'
| 'miss' // check matches after every filesystem miss
| 'hit'
| 'error'; // check matches after error (500, 404, etc.)
type Handler = {
handle: HandleValue;
src?: string;
dest?: string;
status?: number;
};| Key | Type | Required | Description |
|---|---|---|---|
| handle | HandleValue | Yes | The phase of routing when all subsequent routes should apply. |
| src | String | No | A PCRE-compatible regular expression that matches each incoming pathname (excluding querystring). |
| dest | String | No | A destination pathname or full URL, including querystring, with the ability to embed capture groups as $1, $2. |
| status | String | No | A status code to respond with. Can be used in tandem with Location: header to implement redirects. |
The following example shows a routing rule that will cause the /redirect path to perform an HTTP redirect to an external URL:
"routes": [
{
"src": "/redirect",
"status": 308,
"headers": { "Location": "https://example.com/" }
}
].vercel/output/config.json
The images property defines the behavior of Vercel's native Image Optimization API, which allows on-demand optimization of images at runtime.
type ImageFormat = 'image/avif' | 'image/webp';
type RemotePattern = {
protocol?: 'http' | 'https';
hostname: string;
port?: string;
pathname?: string;
search?: string;
};
type LocalPattern = {
pathname?: string;
search?: string;
};
type ImagesConfig = {
sizes: number[];
domains: string[];
remotePatterns?: RemotePattern[];
localPatterns?: LocalPattern[];
minimumCacheTTL?: number; // seconds
formats?: ImageFormat[];
dangerouslyAllowSVG?: boolean;
contentSecurityPolicy?: string;
contentDispositionType?: string;
};| Key | Type | Required | Description |
|---|---|---|---|
| sizes | Number[] | Yes | Supported image widths. |
| domains | String[] | Yes | Allowed external domains that can use Image Optimization. Leave empty for only allowing the deployment domain to use Image Optimization. |
| remotePatterns | RemotePattern[] | No | Allowed external patterns that can use Image Optimization. Similar to domains but provides more control with RegExp. |
| localPatterns | LocalPattern[] | No | Allowed local patterns that can use Image Optimization. Leave undefined to allow all or use empty array to deny all. |
| minimumCacheTTL | Number | No | Cache duration (in seconds) for the optimized images. |
| formats | ImageFormat[] | No | Supported output image formats |
| dangerouslyAllowSVG | Boolean | No | Allow SVG input image URLs. This is disabled by default for security purposes. |
| contentSecurityPolicy | String | No | Change the Content Security Policy of the optimized images. |
| contentDispositionType | String | No | Specifies the value of the "Content-Disposition" response header. |
The following example shows an image optimization configuration that specifies allowed image size dimensions, external domains, caching lifetime and file formats:
"images": {
"sizes": [640, 750, 828, 1080, 1200],
"domains": [],
"minimumCacheTTL": 60,
"formats": ["image/avif", "image/webp"],
"localPatterns": [{
"pathname": "^/assets/.*$",
"search": ""
}]
"remotePatterns": [{
"protocol": "https",
"hostname": "^via\\.placeholder\\.com$",
"port": "",
"pathname": "^/1280x640/.*$",
"search": "?v=1"
}]
}When the images property is defined, the Image Optimization API will be available by visiting the /_vercel/image path. When the images property is undefined, visiting the /_vercel/image path will respond with 404 Not Found.
The API accepts the following query string parameters:
| Key | Type | Required | Example | Description |
|---|---|---|---|---|
| url | String | Yes | /assets/me.png | The URL of the source image that should be optimized. Absolute URLs must match a pattern defined in the remotePatterns configuration. |
| w | Integer | Yes | 200 | The width (in pixels) that the source image should be resized to. Must match a value defined in the sizes configuration. |
| q | Integer | Yes | 75 | The quality that the source image should be reduced to. Must be between 1 (lowest quality) to 100 (highest quality). |
.vercel/output/config.json
The wildcard property relates to Vercel's Internationalization feature. The way
it works is the domain names listed in this array are mapped to the $wildcard
routing variable, which can be referenced by the routes configuration.
Each of the domain names specified in the wildcard configuration will need to
be assigned as Production Domains in the Project Settings.
type WildCard = {
domain: string;
value: string;
};
type WildcardConfig = Array<WildCard>;Objects contained within the wildcard configuration support the following properties:
| Key | Type | Required | Description |
|---|---|---|---|
| domain | String | Yes | The domain name to match for this wildcard configuration. |
| value | String | Yes | The value of the $wildcard match that will be available for routes to utilize. |
The following example shows a wildcard configuration where the matching domain name will be served the localized version of the blog post HTML file:
"wildcard": [
{
"domain": "example.com",
"value": "en-US"
},
{
"domain": "example.nl",
"value": "nl-NL"
},
{
"domain": "example.fr",
"value": "fr"
}
],
"routes": [
{ "src": "/blog", "dest": "/blog.$wildcard.html" }
].vercel/output/config.json
The overrides property allows for overriding the output of one or more static files contained
within the .vercel/output/static directory.
The main use-cases are to override the Content-Type header that will be served for a static file,
and/or to serve a static file in the Vercel Deployment from a different URL path than how it is stored on the file system.
type Override = {
path?: string;
contentType?: string;
};
type OverrideConfig = Record<string, Override>;Objects contained within the overrides configuration support the following properties:
| Key | Type | Required | Description |
|---|---|---|---|
| path | String | No | The URL path where the static file will be accessible from. |
| contentType | String | No | The value of the Content-Type HTTP response header that will be served with the static file. |
The following example shows an override configuration where an HTML file can be accessed
without the .html file extension:
"overrides": {
"blog.html": {
"path": "blog"
}
}.vercel/output/config.json
The cache property is an array of file paths and/or glob patterns that should be re-populated
within the build sandbox upon subsequent Deployments.
Note that this property is only relevant when Vercel is building a Project from source code, meaning it is not relevant when building locally or when creating a Deployment from "prebuilt" build artifacts.
type Cache = string[]; "cache": [
".cache/**",
"node_modules/**"
].vercel/output/config.json
The optional framework property is an object describing the framework of the built outputs.
This value is used for display purposes only.
type Framework = {
version: string;
}; "framework": {
"version": "1.2.3"
}.vercel/output/config.json
The optional crons property is an object describing the cron jobs for the production deployment of a project.
type Cron = {
path: string;
schedule: string;
};
type CronsConfig = Cron[]; "crons": [{
"path": "/api/cron",
"schedule": "0 0 * * *"
}]{
"version": 3,
"routes": [
{
"src": "/redirect",
"status": 308,
"headers": { "Location": "https://example.com/" }
},
{
"src": "/blog",
"dest": "/blog.$wildcard.html"
}
],
"images": {
"sizes": [640, 750, 828, 1080, 1200],
"domains": [],
"minimumCacheTTL": 60,
"formats": ["image/avif", "image/webp"],
"localPatterns": [{
"pathname": "^/assets/.*$",
"search": ""
}]
"remotePatterns": [
{
"protocol": "https",
"hostname": "^via\\.placeholder\\.com$",
"port": "",
"pathname": "^/1280x640/.*$",
"search": "?v=1"
}
]
},
"wildcard": [
{
"domain": "example.com",
"value": "en-US"
},
{
"domain": "example.nl",
"value": "nl-NL"
},
{
"domain": "example.fr",
"value": "fr"
}
],
"overrides": {
"blog.html": {
"path": "blog"
}
},
"cache": [".cache/**", "node_modules/**"],
"framework": {
"version": "1.2.3"
},
"crons": [
{
"path": "/api/cron",
"schedule": "* * * * *"
}
]
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