diff --git a/CHANGELOG.md b/CHANGELOG.md
index 79ade96a..cfaa0017 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -4,7 +4,9 @@ All notable changes to this add-on will be documented in this file.
 The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/).
 
 ## [Unreleased]
-
+### Added
+- extender/arpSyndicateSubdomainDiscovery.js - uses the API of [ARPSyndicate's Subdomain Center](https://www.subdomain.center/)
+  to find and add subdomains to the Sites Tree.
 
 ## [18] - 2024-01-29
 ### Added
diff --git a/extender/arpSyndicateSubdomainDiscovery.js b/extender/arpSyndicateSubdomainDiscovery.js
new file mode 100644
index 00000000..f24d4e95
--- /dev/null
+++ b/extender/arpSyndicateSubdomainDiscovery.js
@@ -0,0 +1,51 @@
+/**
+ * This script uses the API of ARPSyndicate's Subdomain Center (https://www.subdomain.center/) to
+ * find and add subdomains to the Sites Tree. When it is enabled, it runs automatically for each
+ * new domain added to the Sites Tree.
+ */
+
+const HistoryReference = Java.type("org.parosproxy.paros.model.HistoryReference")
+const HttpSender = Java.type("org.parosproxy.paros.network.HttpSender")
+const HttpMessage = Java.type("org.parosproxy.paros.network.HttpMessage")
+const URI = Java.type("org.apache.commons.httpclient.URI")
+const requestedSubdomains = []
+const sender = new HttpSender(HttpSender.MANUAL_REQUEST_INITIATOR)
+
+function consumer(event) {
+    if (event.getEventType() != "site.added") return
+    try {
+        const siteNode = event.getTarget().getStartNode()
+        const host = siteNode.getHistoryReference().getURI().getHost()
+        if (requestedSubdomains.indexOf(host) != -1) {
+            // Don't run for subdomain nodes created by this script
+            return
+        }
+        const apiUri = new URI(`https://api.subdomain.center/?domain=${host}`, true)
+        const apiMsg = new HttpMessage(apiUri)
+        sender.sendAndReceive(apiMsg)
+        const subdomains = JSON.parse(apiMsg.getResponseBody().toString())
+        subdomains.forEach(function (subdomain) {
+            const uri = new URI(`https://${subdomain}`, true)
+            const msg = new HttpMessage(uri)
+            const extHistory = control.getExtensionLoader().getExtension("ExtensionHistory")
+            try {
+                sender.sendAndReceive(msg)
+                const href = new HistoryReference(model.getSession(), HistoryReference.TYPE_ZAP_USER, msg)
+                extHistory.addHistory(href)
+                requestedSubdomains.push(subdomain)
+            } catch (err) {
+                print(`Failed to send a request to "https://${subdomain}": ${err.getMessage()}.`)
+            }
+        })
+    } catch (err) {
+        print(`There was an error while trying to get subdomains using Subdomain Center: ${err}`)
+    }
+}
+
+function install(helper) {
+    org.zaproxy.zap.ZAP.getEventBus().registerConsumer(consumer, "org.parosproxy.paros.model.SiteMapEventPublisher")
+}
+
+function uninstall(helper) {
+    org.zaproxy.zap.ZAP.getEventBus().unregisterConsumer(consumer)
+}