diff --git a/examples/relay/main.cpp b/examples/relay/main.cpp
index 9f810f7..25fa5d9 100644
--- a/examples/relay/main.cpp
+++ b/examples/relay/main.cpp
@@ -59,7 +59,7 @@ public:
             String json;
             serializeJson(resp, json);
             request->send(ok ? 200 : 400, "application/json", json);
-        }, std::vector<ApiServer::ParamSpec>{ ApiServer::ParamSpec{ String("state"), true, String("body"), String("string") } });
+        }, std::vector<ApiServer::ParamSpec>{ ApiServer::ParamSpec{ String("state"), true, String("body"), String("string"), { String("on"), String("off"), String("toggle") } } });
     }
 
     void turnOn() {
diff --git a/include/ApiServer.h b/include/ApiServer.h
index 0366cf8..7bf88ae 100644
--- a/include/ApiServer.h
+++ b/include/ApiServer.h
@@ -28,6 +28,7 @@ public:
         bool required;
         String location; // "query" | "body" | "path" | "header"
         String type;     // e.g. "string", "number", "boolean"
+        std::vector<String> values; // optional allowed values
     };
     struct EndpointCapability {
         String uri;
diff --git a/src/ApiServer.cpp b/src/ApiServer.cpp
index 1c52cb3..e7059f8 100644
--- a/src/ApiServer.cpp
+++ b/src/ApiServer.cpp
@@ -77,8 +77,8 @@ void ApiServer::begin() {
     addEndpoint("/api/tasks/control", HTTP_POST,
         std::bind(&ApiServer::onTaskControlRequest, this, std::placeholders::_1),
         std::vector<ParamSpec>{
-            ParamSpec{String("task"), true, String("body"), String("string")},
-            ParamSpec{String("action"), true, String("body"), String("string")}
+            ParamSpec{String("task"), true, String("body"), String("string"), {}},
+            ParamSpec{String("action"), true, String("body"), String("string"), {String("enable"), String("disable"), String("start"), String("stop"), String("status")}}
         }
     );
     
@@ -370,6 +370,12 @@ void ApiServer::onCapabilitiesRequest(AsyncWebServerRequest *request) {
                 p["location"] = ps.location;
                 p["required"] = ps.required;
                 p["type"] = ps.type;
+                if (!ps.values.empty()) {
+                    JsonArray allowed = p["values"].to<JsonArray>();
+                    for (const auto& v : ps.values) {
+                        allowed.add(v);
+                    }
+                }
             }
         }
     }