diff --git a/scripts/indexnow.mjs b/scripts/indexnow.mjs
new file mode 100644
index 0000000..00f012c
--- /dev/null
+++ b/scripts/indexnow.mjs
@@ -0,0 +1,73 @@
+#!/usr/bin/env node
+/**
+ * Tell the IndexNow participants (Bing, Yandex, Naver, Seznam, Yep) that the
+ * site's pages changed. Google is not a participant.
+ *
+ * A command someone runs after a change worth announcing, not a deploy step:
+ * submitting unchanged pages on every build is how a domain earns a rate limit.
+ *
+ *     node scripts/indexnow.mjs <host>
+ *     node scripts/indexnow.mjs <host> --dry-run
+ *
+ * The host is an argument because the domain lives in the deploy settings, not
+ * in this repo. The pages come from the deployed sitemap, so a new page is
+ * announced without anyone remembering to list it.
+ *
+ * The key is not a secret: IndexNow checks ownership by reading it back from
+ * the domain it is for, so it is public by design.
+ */
+
+const KEY = '07d125e7231655dd8670b5fb9f6f9aed'
+const ENDPOINT = 'https://api.indexnow.org/indexnow'
+
+const host = process.argv.slice(2).find((a) => !a.startsWith('--'))
+const dryRun = process.argv.includes('--dry-run')
+if (!host) {
+  console.error('usage: node scripts/indexnow.mjs <host> [--dry-run]')
+  process.exit(2)
+}
+
+// Submitting before the key file is reachable is refused without saying why,
+// so check it first and name the cause.
+const keyLocation = `https://${host}/${KEY}.txt`
+const hosted = await fetch(keyLocation).catch(() => undefined)
+if (!hosted?.ok || (await hosted.text()).trim() !== KEY) {
+  console.error(`${keyLocation} does not serve the key; deploy first.`)
+  process.exit(1)
+}
+
+const sitemap = await fetch(`https://${host}/sitemap.xml`).catch(() => undefined)
+if (!sitemap?.ok) {
+  console.error(`Could not read https://${host}/sitemap.xml.`)
+  process.exit(1)
+}
+const urlList = [...(await sitemap.text()).matchAll(/<loc>([^<]+)<\/loc>/g)].map((m) => m[1])
+if (urlList.length === 0) {
+  console.error('The sitemap lists no pages.')
+  process.exit(1)
+}
+
+const body = { host, key: KEY, keyLocation, urlList }
+if (dryRun) {
+  console.log(JSON.stringify(body, null, 2))
+  process.exit(0)
+}
+
+const response = await fetch(ENDPOINT, {
+  method: 'POST',
+  headers: { 'content-type': 'application/json; charset=utf-8' },
+  body: JSON.stringify(body),
+})
+// 200 is accepted; 202 is accepted while the key is still being checked.
+if (response.status === 200 || response.status === 202) {
+  console.log(`Submitted ${urlList.length} URLs (HTTP ${response.status}).`)
+  process.exit(0)
+}
+const why = {
+  400: 'the request was malformed',
+  403: 'the key was rejected for this host',
+  422: 'a URL did not belong to this host, or the key did not match',
+  429: 'too many submissions; wait rather than retrying',
+}
+console.error(`IndexNow refused it: HTTP ${response.status}, ${why[response.status] ?? 'unknown'}`)
+process.exit(1)