Custom builds

Last updated Apr 23, 2026 Custom builds are a way for you to customize how your code is compiled, before being processed by Wrangler.

Note

Wrangler runs esbuild ↗︎ by default as part of the dev and deploy commands, and bundles your Worker project into a single Worker script. Refer to Bundling.

Configure custom builds

Custom builds are configured by adding a [build] section in your Wrangler configuration file, and using the following options for configuring your custom build.

• command string optional
• The command used to build your Worker. On Linux and macOS, the command is executed in the sh shell and the cmd shell for Windows. The && and || shell operators may be used. This command will be run as part of wrangler dev and npx wrangler deploy.
• cwd string optional
• The directory in which the command is executed.
• watch_dir string | string\[] optional
• The directory to watch for changes while using wrangler dev. Defaults to the current working directory.

Example:

{
    "build": {
        "command": "npm run build",
        "cwd": "build_cwd",
        "watch_dir": "build_watch_dir"
    }
}

[build]
command = "npm run build"
cwd = "build_cwd"
watch_dir = "build_watch_dir"

WRANGLER_COMMAND environment variable

When Wrangler runs your custom build command, it sets the WRANGLER_COMMAND environment variable so your build script can detect which Wrangler command triggered the build. This allows you to customize the build process based on the deployment context.

The possible values are:

For example, you can use this to apply different build settings for development and production:

#!/bin/bash
if [ "$WRANGLER_COMMAND" = "dev" ]; then
  echo "Building for development..."
  # run a development build
else
  echo "Building for production..."
  # run a production build
fi

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