diff --git a/esphome/components/web_server/web_server.cpp b/esphome/components/web_server/web_server.cpp
index d06b6d6408..3fe3979a8b 100644
--- a/esphome/components/web_server/web_server.cpp
+++ b/esphome/components/web_server/web_server.cpp
@@ -1115,6 +1115,7 @@ json::SerializationBuffer<> WebServer::cover_json_(cover::Cover *obj, JsonDetail
   if (obj->get_traits().get_supports_tilt())
     root[ESPHOME_F("tilt")] = obj->tilt;
   if (start_config == DETAIL_ALL) {
+    root[ESPHOME_F("assumed_state")] = obj->get_traits().get_is_assumed_state();
     this->add_sorting_info_(root, obj);
   }
 
diff --git a/tests/components/web_server/common.yaml b/tests/components/web_server/common.yaml
index 5a05a58c2d..d7b880efe6 100644
--- a/tests/components/web_server/common.yaml
+++ b/tests/components/web_server/common.yaml
@@ -4,6 +4,17 @@ wifi:
 
 binary_sensor:
 cover:
+  - platform: template
+    name: "Template Cover Assumed"
+    # assumed_state must be reflected in the web_server JSON (detail=all)
+    assumed_state: true
+    lambda: 'return COVER_OPEN;'
+    open_action:
+      - logger.log: open_action
+    close_action:
+      - logger.log: close_action
+    stop_action:
+      - logger.log: stop_action
 fan:
 light:
 sensor: