The Sitemap integration requires the `site` astro.config opt

Error message

The Sitemap integration requires the `site` astro.config option. Skipping.

What it means

The Sitemap integration needs an absolute origin to prefix every generated URL, and it takes that origin solely from the top-level site option in astro.config. In its astro:build:done hook it checks config.site; when absent it logs this warning and returns early, so no sitemap-index.xml is written even though the build itself succeeds.

Source

Thrown at packages/integrations/sitemap/src/index.ts:101

	let _routes: Array<IntegrationResolvedRoute>;
	let config: AstroConfig;

	return {
		name: PKG_NAME,

		hooks: {
			'astro:routes:resolved': ({ routes }) => {
				_routes = routes;
			},

			'astro:config:done': async ({ config: cfg }) => {
				config = cfg;
			},

			'astro:build:done': async ({ dir, pages, logger }) => {
				try {
					if (!config.site) {
						logger.warn(
							'The Sitemap integration requires the `site` astro.config option. Skipping.',
						);
						return;
					}

					const opts = validateOptions(config.site, options);

					const {
						filenameBase,
						filter,
						customPages,
						customSitemaps,
						serialize,
						entryLimit,
						chunks,
					} = opts;
					const outFile = `${filenameBase}-index.xml`;
					const finalSiteUrl = new URL(config.base, config.site);

View on GitHub (pinned to 157c500c38)

Solutions

Set site in astro.config.mjs: export default defineConfig({ site: 'https://www.example.com', integrations: [sitemap()] });
If the domain varies by environment, derive it from an env var: site: process.env.SITE_URL (ensure it is set in CI).
Rebuild and verify dist/sitemap-index.xml is generated.

Example fix

// before
export default defineConfig({
  integrations: [sitemap()],
});

// after
export default defineConfig({
  site: 'https://www.example.com',
  integrations: [sitemap()],
});

Defensive patterns

Strategy: validation

Validate before calling

// fail the build early if site is missing while sitemap is enabled
const config = await import('./astro.config.mjs').then((m) => m.default);
if (config.integrations.some((i) => i.name === 'astro-sitemap') && !config.site) {
  throw new Error('sitemap() requires the `site` config option');
}

Type guard

const hasSite = (config: { site?: string }): config is { site: string } =>
  typeof config.site === 'string' && /^https?:\/\//.test(config.site);

Prevention

Set site in astro.config as part of adding the sitemap integration.
If SITE_URL comes from an env var, assert it is present before running astro build in CI.
Check the build log for 'sitemap-index.xml' output or verify dist/ after every production build.

When it happens

Trigger: Running astro build with the sitemap() integration but no site: 'https://example.com' in defineConfig. The astro:build:done hook sees config.site undefined, warns, and skips validateOptions/generateSitemap entirely.

Common situations: New projects or previews deployed to temporary preview URLs (no production domain yet); CI builds where site is meant to come from an env var that was not set; forgetting that dev-only sites still need site for sitemap generation.

Related errors

AI-assisted analysis of withastro/astro@157c500c38 (2026-08-18). Data as JSON: /api/errors/b2e593915c28be94. Report an issue: GitHub.