diff --git a/DEVELOPMENT.md b/DEVELOPMENT.md
index 531fa98..a58b26d 100644
--- a/DEVELOPMENT.md
+++ b/DEVELOPMENT.md
@@ -198,6 +198,7 @@ Ergaenzt seit dem ersten Geruest:
 - letzter bekannter Player-Status wird im Backend pro Screen in-memory vorgehalten und lesbar gemacht
 - Backend ergaenzt den Read-Pfad um `received_at` und eine einfache `stale`-Ableitung
 - Backend bietet zusaetzlich eine kleine Uebersicht aller zuletzt meldenden Screens
+- Backend validiert den Statuspfad jetzt enger auf erlaubte Lifecycle-/Connectivity-Werte und leitet `stale` aus dem gemeldeten Intervall ab
 - dateibasierte Agent-Konfiguration zusaetzlich zu Env-Overrides
 - strukturierte Agent-Logs mit internem Health-Snapshot und signalgesteuertem Shutdown
 - erster periodischer HTTP-Status-Reporter im Agent
diff --git a/docs/PLAYER-STATUS-HTTP.md b/docs/PLAYER-STATUS-HTTP.md
index 317bd34..f113f60 100644
--- a/docs/PLAYER-STATUS-HTTP.md
+++ b/docs/PLAYER-STATUS-HTTP.md
@@ -24,6 +24,12 @@ Mindestens enthalten:
 - `ts`
 - `status`
 
+Fuer die aktuelle Entwicklungsstufe sind zulaessig:
+
+- `status`: `starting`, `running`, `stopped`
+- `server_connectivity`: `unknown`, `online`, `degraded`, `offline`
+- `heartbeat_every_seconds`: positive Ganzzahl
+
 Aktuell zusaetzlich enthalten:
 
 - `server_connectivity`
@@ -81,6 +87,7 @@ Zusaetzlich fuegt das Backend im Read-Pfad derzeit hinzu:
 - `stale` als einfache serverseitige Einordnung, ob der letzte Report bereits veraltet wirkt
 
 `stale` ist aktuell bewusst nur eine kleine Diagnosehilfe fuer die Entwicklungsstufe und noch kein vollstaendiges Online-/Offline-Modell fuer spaetere Admin-Oberflaechen.
+Die Schwelle wird derzeit einfach aus dem gemeldeten `heartbeat_every_seconds` abgeleitet: mehr als zwei Intervalle ohne neuen Report gelten als veraltet.
 
 ## Abgrenzung
 
diff --git a/server/backend/internal/httpapi/playerstatus.go b/server/backend/internal/httpapi/playerstatus.go
index bd78116..a7d53db 100644
--- a/server/backend/internal/httpapi/playerstatus.go
+++ b/server/backend/internal/httpapi/playerstatus.go
@@ -6,7 +6,19 @@ import (
 	"time"
 )
 
-const staleThreshold = 2 * time.Minute
+var allowedStatuses = map[string]struct{}{
+	"starting": {},
+	"running":  {},
+	"stopped":  {},
+}
+
+var allowedServerConnectivity = map[string]struct{}{
+	"":         {},
+	"unknown":  {},
+	"online":   {},
+	"degraded": {},
+	"offline":  {},
+}
 
 type playerStatusRequest struct {
 	ScreenID              string `json:"screen_id"`
@@ -43,6 +55,22 @@ func handlePlayerStatus(store playerStatusStore) http.HandlerFunc {
 			writeError(w, http.StatusBadRequest, "status_required", "status ist erforderlich", nil)
 			return
 		}
+		request.Status = strings.TrimSpace(request.Status)
+		if _, ok := allowedStatuses[request.Status]; !ok {
+			writeError(w, http.StatusBadRequest, "invalid_status", "status ist ungueltig", nil)
+			return
+		}
+
+		request.ServerConnectivity = strings.TrimSpace(request.ServerConnectivity)
+		if _, ok := allowedServerConnectivity[request.ServerConnectivity]; !ok {
+			writeError(w, http.StatusBadRequest, "invalid_server_connectivity", "server_connectivity ist ungueltig", nil)
+			return
+		}
+
+		if request.HeartbeatEverySeconds <= 0 {
+			writeError(w, http.StatusBadRequest, "invalid_heartbeat_interval", "heartbeat_every_seconds muss positiv sein", nil)
+			return
+		}
 
 		if err := validateOptionalRFC3339(request.Timestamp); err != nil {
 			writeError(w, http.StatusBadRequest, "invalid_timestamp", "ts ist kein gueltiger RFC3339-Zeitstempel", nil)
@@ -129,5 +157,14 @@ func isStale(record playerStatusRecord, now time.Time) bool {
 		return false
 	}
 
-	return now.Sub(receivedAt) > staleThreshold
+	threshold := staleThresholdFor(record)
+	return now.Sub(receivedAt) > threshold
+}
+
+func staleThresholdFor(record playerStatusRecord) time.Duration {
+	if record.HeartbeatEverySeconds > 0 {
+		return time.Duration(record.HeartbeatEverySeconds*2) * time.Second
+	}
+
+	return 2 * time.Minute
 }
diff --git a/server/backend/internal/httpapi/playerstatus_test.go b/server/backend/internal/httpapi/playerstatus_test.go
index 3215521..63d9d93 100644
--- a/server/backend/internal/httpapi/playerstatus_test.go
+++ b/server/backend/internal/httpapi/playerstatus_test.go
@@ -95,7 +95,8 @@ func TestHandlePlayerStatusStoresNormalizedScreenID(t *testing.T) {
 	body := []byte(`{
 		"screen_id": "  info01-dev  ",
 		"ts": "2026-03-22T16:00:00Z",
-		"status": "running"
+		"status": "running",
+		"heartbeat_every_seconds": 30
 	}`)
 
 	req := httptest.NewRequest(http.MethodPost, "/api/v1/player/status", bytes.NewReader(body))
@@ -144,6 +145,59 @@ func TestHandlePlayerStatusRejectsMissingStatus(t *testing.T) {
 	}
 }
 
+func TestHandlePlayerStatusRejectsUnknownStatus(t *testing.T) {
+	body := []byte(`{
+		"screen_id": "info01-dev",
+		"ts": "2026-03-22T16:00:00Z",
+		"status": "broken"
+	}`)
+
+	req := httptest.NewRequest(http.MethodPost, "/api/v1/player/status", bytes.NewReader(body))
+	w := httptest.NewRecorder()
+
+	handlePlayerStatus(newInMemoryPlayerStatusStore())(w, req)
+
+	if got, want := w.Code, http.StatusBadRequest; got != want {
+		t.Fatalf("status = %d, want %d", got, want)
+	}
+}
+
+func TestHandlePlayerStatusRejectsUnknownServerConnectivity(t *testing.T) {
+	body := []byte(`{
+		"screen_id": "info01-dev",
+		"ts": "2026-03-22T16:00:00Z",
+		"status": "running",
+		"server_connectivity": "maybe"
+	}`)
+
+	req := httptest.NewRequest(http.MethodPost, "/api/v1/player/status", bytes.NewReader(body))
+	w := httptest.NewRecorder()
+
+	handlePlayerStatus(newInMemoryPlayerStatusStore())(w, req)
+
+	if got, want := w.Code, http.StatusBadRequest; got != want {
+		t.Fatalf("status = %d, want %d", got, want)
+	}
+}
+
+func TestHandlePlayerStatusRejectsNonPositiveHeartbeatInterval(t *testing.T) {
+	body := []byte(`{
+		"screen_id": "info01-dev",
+		"ts": "2026-03-22T16:00:00Z",
+		"status": "running",
+		"heartbeat_every_seconds": 0
+	}`)
+
+	req := httptest.NewRequest(http.MethodPost, "/api/v1/player/status", bytes.NewReader(body))
+	w := httptest.NewRecorder()
+
+	handlePlayerStatus(newInMemoryPlayerStatusStore())(w, req)
+
+	if got, want := w.Code, http.StatusBadRequest; got != want {
+		t.Fatalf("status = %d, want %d", got, want)
+	}
+}
+
 func TestHandlePlayerStatusRejectsMalformedTimestamps(t *testing.T) {
 	body := []byte(`{
 		"screen_id": "info01-dev",
@@ -277,6 +331,36 @@ func TestHandleGetLatestPlayerStatusMarksStaleRecords(t *testing.T) {
 	}
 }
 
+func TestHandleGetLatestPlayerStatusUsesHeartbeatIntervalForFreshness(t *testing.T) {
+	store := newInMemoryPlayerStatusStore()
+	store.now = func() time.Time {
+		return time.Date(2026, 3, 22, 16, 3, 30, 0, time.UTC)
+	}
+	store.Save(playerStatusRecord{
+		ScreenID:              "slow-screen",
+		Timestamp:             "2026-03-22T16:00:00Z",
+		Status:                "running",
+		ServerConnectivity:    "online",
+		ReceivedAt:            "2026-03-22T16:00:00Z",
+		HeartbeatEverySeconds: 120,
+	})
+
+	req := httptest.NewRequest(http.MethodGet, "/api/v1/screens/slow-screen/status", nil)
+	req.SetPathValue("screenId", "slow-screen")
+	w := httptest.NewRecorder()
+
+	handleGetLatestPlayerStatus(store)(w, req)
+
+	var response playerStatusRecord
+	if err := json.Unmarshal(w.Body.Bytes(), &response); err != nil {
+		t.Fatalf("Unmarshal() error = %v", err)
+	}
+
+	if got, want := response.Stale, false; got != want {
+		t.Fatalf("response.Stale = %v, want %v", got, want)
+	}
+}
+
 func TestHandleGetLatestPlayerStatusNotFound(t *testing.T) {
 	req := httptest.NewRequest(http.MethodGet, "/api/v1/screens/missing/status", nil)
 	req.SetPathValue("screenId", "missing")
diff --git a/server/backend/internal/httpapi/router_test.go b/server/backend/internal/httpapi/router_test.go
index 423d2de..2735b6a 100644
--- a/server/backend/internal/httpapi/router_test.go
+++ b/server/backend/internal/httpapi/router_test.go
@@ -139,7 +139,7 @@ func TestRouterMeta(t *testing.T) {
 }
 
 func TestRouterPlayerStatusRoute(t *testing.T) {
-	req := httptest.NewRequest(http.MethodPost, "/api/v1/player/status", bytes.NewBufferString(`{"screen_id":"demo","ts":"2026-03-22T16:00:00Z","status":"running"}`))
+	req := httptest.NewRequest(http.MethodPost, "/api/v1/player/status", bytes.NewBufferString(`{"screen_id":"demo","ts":"2026-03-22T16:00:00Z","status":"running","heartbeat_every_seconds":30}`))
 	w := httptest.NewRecorder()
 
 	NewRouter(newInMemoryPlayerStatusStore()).ServeHTTP(w, req)