diff --git a/docs/releases.md b/docs/releases.md
index 71e64fea..77588cf1 100644
--- a/docs/releases.md
+++ b/docs/releases.md
@@ -1669,5 +1669,6 @@ and the [ntfy Android app](https://github.com/binwiederhier/ntfy-android/release
 
 **Bug fixes + maintenance:**
 
+* Web: Add validation feedback for service URL when adding user ([#1566](https://github.com/binwiederhier/ntfy/issues/1566), thanks to [@jermanuts](https://github.com/jermanuts))
 * Docs: Remove obsolete `version` field from docker-compose examples ([#1333](https://github.com/binwiederhier/ntfy/issues/1333), thanks to [@seals187](https://github.com/seals187) for reporting and [@cyb3rko](https://github.com/cyb3rko) for fixing)
 * Docs: Fix Kustomize config - correct volumeMount path and volumes indentation ([#1367](https://github.com/binwiederhier/ntfy/issues/1367), thanks to [@toby-griffiths](https://github.com/toby-griffiths))
diff --git a/web/public/static/langs/en.json b/web/public/static/langs/en.json
index 15e78976..19fe2195 100644
--- a/web/public/static/langs/en.json
+++ b/web/public/static/langs/en.json
@@ -357,6 +357,8 @@
   "prefs_users_dialog_title_add": "Add user",
   "prefs_users_dialog_title_edit": "Edit user",
   "prefs_users_dialog_base_url_label": "Service URL, e.g. https://ntfy.sh",
+  "prefs_users_dialog_base_url_invalid": "Invalid URL format. Must start with http:// or https://",
+  "prefs_users_dialog_base_url_exists": "A user for this service URL already exists",
   "prefs_users_dialog_username_label": "Username, e.g. phil",
   "prefs_users_dialog_password_label": "Password",
   "prefs_appearance_title": "Appearance",
diff --git a/web/src/components/Preferences.jsx b/web/src/components/Preferences.jsx
index 8621a263..bd97da3a 100644
--- a/web/src/components/Preferences.jsx
+++ b/web/src/components/Preferences.jsx
@@ -429,13 +429,14 @@ const UserDialog = (props) => {
   const [password, setPassword] = useState("");
   const fullScreen = useMediaQuery(theme.breakpoints.down("sm"));
   const editMode = props.user !== null;
+  const baseUrlValid = baseUrl.length === 0 || validUrl(baseUrl);
+  const baseUrlExists = props.users?.map((user) => user.baseUrl).includes(baseUrl);
+  const baseUrlError = baseUrl.length > 0 && (!baseUrlValid || baseUrlExists);
   const addButtonEnabled = (() => {
     if (editMode) {
       return username.length > 0 && password.length > 0;
     }
-    const baseUrlValid = validUrl(baseUrl);
-    const baseUrlExists = props.users?.map((user) => user.baseUrl).includes(baseUrl);
-    return baseUrlValid && !baseUrlExists && username.length > 0 && password.length > 0;
+    return validUrl(baseUrl) && !baseUrlExists && username.length > 0 && password.length > 0;
   })();
   const handleSubmit = async () => {
     props.onSubmit({
@@ -467,6 +468,14 @@ const UserDialog = (props) => {
             type="url"
             fullWidth
             variant="standard"
+            error={baseUrlError}
+            helperText={
+              baseUrl.length > 0 && !baseUrlValid
+                ? t("prefs_users_dialog_base_url_invalid")
+                : baseUrlExists
+                  ? t("prefs_users_dialog_base_url_exists")
+                  : ""
+            }
           />
         )}
         <TextField