diff --git a/examples/server/server.cpp b/examples/server/server.cpp
index 22230b4c04df7..809c8d7e50172 100644
--- a/examples/server/server.cpp
+++ b/examples/server/server.cpp
@@ -2693,9 +2693,9 @@ int main(int argc, char ** argv) {
         res.set_content(health.dump(), "application/json");
     };
 
-    const auto handle_slots = [&](const httplib::Request &, httplib::Response & res) {
+    const auto handle_slots = [&](const httplib::Request & req, httplib::Response & res) {
         if (!params.endpoint_slots) {
-            res_error(res, format_error_response("This server does not support slots endpoint.", ERROR_TYPE_NOT_SUPPORTED));
+            res_error(res, format_error_response("This server does not support slots endpoint. Start it without `--no-slots`", ERROR_TYPE_NOT_SUPPORTED));
             return;
         }
 
@@ -2713,13 +2713,22 @@ int main(int argc, char ** argv) {
         server_task_result result = ctx_server.queue_results.recv(task.id);
         ctx_server.queue_results.remove_waiting_task_id(task.id);
 
+        // optionally return "fail_on_no_slot" error
+        const int n_idle_slots = result.data.at("idle");
+        if (req.has_param("fail_on_no_slot")) {
+            if (n_idle_slots == 0) {
+                res_error(res, format_error_response("no slot available", ERROR_TYPE_UNAVAILABLE));
+                return;
+            }
+        }
+
         res.set_content(result.data.at("slots").dump(), MIMETYPE_JSON);
         res.status = 200; // HTTP OK
     };
 
     const auto handle_metrics = [&](const httplib::Request &, httplib::Response & res) {
         if (!params.endpoint_metrics) {
-            res_error(res, format_error_response("This server does not support metrics endpoint.", ERROR_TYPE_NOT_SUPPORTED));
+            res_error(res, format_error_response("This server does not support metrics endpoint. Start it with `--metrics`", ERROR_TYPE_NOT_SUPPORTED));
             return;
         }