Build Step

When you trigger a deploy, Vercel builds your project. For many frontend frameworks, Vercel automatically configures the build settings, but you can also customize them. You can also use environment variables to avoid hardcoding values.

Customizing Build Settings

To customize the build settings for your project, choose a project from the dashboard:

Selecting the project from the Vercel Dashboard.

Then, select the Settings tab:

Selecting the Settings tab from the Project Overview page.

You can then edit the build settings from the Build & Development Settings, Root Directory, and Environment Variables sections.

Build & Development Settings

​Vercel tries to automatically detect the frontend framework you’re using for your project and configure the project settings for you. If you’d like to override the settings or specify a different framework, you can do so from the Build & Development Settings section.

Framework Preset

The Framework Preset setting.

​Vercel detects the following frontend frameworks automatically and chooses the best default settings for you.

If no framework is detected, "Other" will be selected for you.

You can always choose a different framework preset or "Other" if you’d like.

Build Command

The Build Command setting.

If Vercel detects a framework, the Build Command will automatically be configured. Depending on a framework, the Build Command can refer to the project’s configuration file.

For example, if you choose Next.js, here’s what happens by default:

• If package.json contains the build command in scripts, this command will be used to build the project.
• If not, next build will be the Build Command.

If you’d like to override the Build Command, you can turn on the Override toggle and specify the command.

Skip Build Step

Some static projects do not require building. An example of this would be a website with only HTML/CSS/JS source files that can be served as-is (For example, you might just have a single index.html file).

In such cases, you should:

• Specify "Other" as the framework preset, and
• Enable the Override option for the Build Command, and
• Leave the Build Command empty.

This will prevent the build from being attempted and serve your content as-is.

Output Directory

The Output Directory setting.

After building a project, most frameworks will output the result in a directory. Contents in this output directory will be the only things that will be statically served by Vercel.

If Vercel detects a framework, the output directory will automatically be configured.

In some cases, your project might not require building, and you might just want to serve the files in the root directory. If so, try the following:

• Choose "Other" as the framework preset. If you do so, by default, the output directory will be set as public if it exists, or . (current directory) otherwise.
• Therefore, as long as your project doesn’t have the public directory, it will serve the files in the root directory.
• Alternatively, you can turn on the Override toggle and leave the field empty (in which case, the build step will be skipped).

Development Command

The Development Command setting.

The Development Command setting allows you to customize the behavior of vercel dev. If Vercel detects a framework, the development command will automatically be configured.

If you’d like to use a custom command for vercel dev, you can turn on the Override toggle. Please note the following:

• If you specify a custom command, your command must pass the $PORT variable (which contains the port number) to your framework. For example, for Next.js, you should use: next dev --port $PORT.
• If the development command is not specified, vercel dev will fail. If you selected "Other" as the framework preset, the development command will be empty by default.
• You must create a deployment and have your local project be linked to the project on Vercel (using vercel). Otherwise, vercel dev won’t work correctly.

Root Directory

The Root Directory setting.

In some projects, the top-level directory of the repository may not be the root directory of the app you’d like to build. For example, your repository might have a frontend directory, which contains a stand-alone Next.js app.

In cases like this, you can specify the project root directory. If you do so, please note the following:

• If you specify a root directory, then your app won’t be able to access files outside of that directory. You also cannot use .. to move up a level.
• This setting also applies to Vercel CLI. Instead of running vercel <directory-name> to deploy, specify <directory-name> here so you can just run vercel.

Environment Variables

Environment Variables are accessible during both Build Step and Runtime, and can be configured for Production, Preview, and Development Environments individually.

This allows you to include values that you don't want to share in your code or to change the behavior of your code depending on its Environment.

To declare an Environment Variable for your deployment, head to the Environment Variables page of your Project Settings.

The Environment Variables settings.

First, choose between the following Environments:

Enter the Name of the Environment Variable. For example, if you are using Node.js and you create an Environment Variable named SENTRY_KEY, it will be available under process.env.SENTRY_KEY in your code.

Then, enter the Value of the Environment Variable. The value is automatically encrypted and stored as a Secret in our system when you click Add.

Adding an Environment Variable in the Project Settings.

Once added, the Environment Variable is applied to your subsequent deployment. It can then be consumed during Build Step by the framework of your choice, or by a Serverless Function at Runtime.

Development Environment Variables

Environment Variables created for the Development Environment can be downloaded into a local development setup using the vercel env pull command provided by Vercel CLI:

vercel env pull
Downloading Development Environment Variables for project my-lovely-project
✅ Created .env file [510ms]

Downloading Development Environment Variables with `vercel env pull`.

Running the command will create a .env file in your project folder. The .env file can then be consumed by vercel dev or your preferred development command.

Check out the Vercel CLI reference to learn more about vercel env commands.

Integration Environment Variables

Integrations can automatically add Environment Variables to your Project Settings. In that case, the Integration Configuration that added it will be displayed:

Adding an Integration Environment Variable in the Project Settings.

System Environment Variables

​Vercel provides a set of Environment Variables that are optionally populated by the System, such as the URL of the Deployment or the name of the Git branch deployed.

To apply a System Environment Variable to your Deployment, enter its Name, leave the Value empty, and click Add.

Adding a System Environment Variable in the Project Settings.

The following System Environment Variables are available:

Reserved Environment Variables

The Vercel platform reserves the usage of some Environment Variable names by default. You can find a list of these names in the limits documentation.

Using a .env File

We generally recommend only adding your Environment Variables in the Project Settings, as that's the only way to achieve different Environment Variables based on the Environment (Development, Preview or Production).

Therefore, it's not necessary to use a .env file or configure Environment Variables within the vercel.json file.

Ignored Files and Folders

By default, Vercel ignores certain files and folders for security and performance reasons, preventing them from being uploaded during the deployment process.

.hg/
.git/
.gitmodules
.svn/
.cache
.next/
.now/
.vercel/
.npmignore
.dockerignore
.gitignore
.*.swp
.DS_Store
.wafpicke-*
.lock-wscript
.env.local
.env.*.local
.venv
npm-debug.log
config.gypi
node_modules/
__pycache__/
venv/
CVS

A complete list of files and folders ignored by Vercel during the deployment process.

Technical Details

Maximum Build Duration

A build can last for a maximum of 30 minutes. If the build exceeds this time, the deployment will error.

Caching

Each build step will cache files used to build the project, or files used in subsequent deployments, such as node_modules, yarn.lock, package-lock.json, which are cached by default.

The caching mechanism for builds ensures that the next deployment will happen quicker by skipping downloading files that have already been used in a previous deployment.

The maximum stored cache for builds is 500MB.

If a deployment fails, a cache may still be established for successfully built files, but failed builds will not be cached.

Private npm Modules for Static Builds

To install private npm modules, define NPM_TOKEN as a build environment variable in a vercel.json file.

Alternatively, define NPM_RC as a build environment variable with the contents of ~/.npmrc.

Prevent Installing Development Dependencies

In some rare cases, you may wish to skip installing devDependencies defined in your package.json file and only install dependencies.

This can be achieved by assigning NPM_ONLY_PRODUCTION=1 as a build environment variable.

This is equivalent to npm install --only=production or yarn install --production.

Prevent Cache Usage

If you need to ignore the cache for a deployment, you can do so by using the -f flag for Vercel CLI. This prevents the cache from being used in the deployment and ensures a fresh install for all dependencies.

Framework Versioning

Some frameworks do not use package.json to select a specific version to install during build time.

By including a build.env configuration property in a vercel.json file at your project's root, you can define your framework's version with one of the following keys:

For example, defining the Hugo version in a vercel.json file would look like the following snippet:

{
  "build": {
    "env": {
      "HUGO_VERSION": "0.61.0"
    }
  }
}

An example of defining a version for Hugo with a vercel.json configuration.

Related

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