Example of a dynamic robots.txt that is sensitive to .env

robots-txt.ts

// routes/robots.txt/+server.ts
import { env } from "$env/dynamic/private";

export function GET() {
  let rules = [
    'User-agent: *'
  ]

  if(env.ORIGIN === 'https://example.com') {
    rules.push('Disallow: /*.js$')
    rules.push('Disallow: /*.json')
    rules.push('Sitemap: https://example.com/sitemap.xml')
  } else {
    // Disable all indexing for staging (and any other environment, just in case)
    rules.push('Disallow: /')
  }

  const body = rules.join('\n').trim();

	return new Response(body,
		{
			headers: {
				'Content-Type': 'text/plain'
			}
		}
	);
}