diff --git a/CHANGELOG.md b/CHANGELOG.md
index eb77f27f..e3f3f024 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -11,6 +11,10 @@ The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.1.0/).
 - OCI labels missing from `docker/metadata-action` on the Topograph container image: `org.opencontainers.image.documentation`, `authors`, and `vendor` ([#377](https://github.com/NVIDIA/topograph/pull/377)).
 - Helm chart metadata: `home`, `icon`, `maintainers`, `keywords`, and Artifact Hub annotations ([#377](https://github.com/NVIDIA/topograph/pull/377)).
 
+### Changed
+
+- Slinky engine `useGpuCliqueLabel` now emits an actionable diagnostic when no block domains can be built: the error reports how many nodes were scanned and why each was skipped (no Slurm mapping, missing `nvidia.com/gpu.clique` label, or missing the node-data-broker-written `topograph.nvidia.com/instance` annotation), and lists the offending node names.
+
 ### Fixed
 
 - Helm node-observer now targets the rendered Topograph Service fullname in `generateTopologyUrl`.
diff --git a/pkg/engines/slinky/engine.go b/pkg/engines/slinky/engine.go
index b7c3b08e..12450fbb 100644
--- a/pkg/engines/slinky/engine.go
+++ b/pkg/engines/slinky/engine.go
@@ -262,21 +262,35 @@ func getComputeInstances(nodes *corev1.NodeList, nodeMap map[string]string) ([]t
 
 func withGPUCliqueDomains(graph *topology.Graph, clusterNodes *clusterNodes) (*topology.Graph, *httperr.Error) {
 	domains := topology.NewDomainMap()
+
+	// Diagnostic counters to explain why no domains were built. The instance
+	// annotation is written per-node by the node-data-broker DaemonSet, so a
+	// node with the clique label but no annotation points at a broker that has
+	// not (yet) annotated that specific node.
+	totalNodes := len(clusterNodes.nodes.Items)
+	var noSlurmName, noCliqueLabel int
+	missingAnnotation := []string{}
+
 	for _, node := range clusterNodes.nodes.Items {
 		slurmName, ok := clusterNodes.nodeMap[node.Name]
 		if !ok || slurmName == "" {
+			noSlurmName++
 			klog.V(4).Infof("Skipping node %s as it does not have a corresponding SLURM name", node.Name)
 			continue
 		}
 
 		gpuClique := strings.TrimSpace(node.Labels[topology.KeyNvidiaGPUClique])
 		if gpuClique == "" {
+			noCliqueLabel++
+			klog.V(4).Infof("Skipping node %s (SLURM node %s): missing/empty %q label", node.Name, slurmName, topology.KeyNvidiaGPUClique)
 			continue
 		}
 
 		instance, ok := node.Annotations[topology.KeyNodeInstance]
 		if !ok {
-			klog.Warningf("missing %q annotation in node %s", topology.KeyNodeInstance, node.Name)
+			missingAnnotation = append(missingAnnotation, node.Name)
+			klog.Warningf("node %s (SLURM node %s) has label %s=%q but is missing annotation %q (expected from node-data-broker on that node)",
+				node.Name, slurmName, topology.KeyNvidiaGPUClique, gpuClique, topology.KeyNodeInstance)
 			continue
 		}
 
@@ -285,8 +299,11 @@ func withGPUCliqueDomains(graph *topology.Graph, clusterNodes *clusterNodes) (*t
 
 	if len(domains) == 0 {
 		return nil, httperr.NewError(http.StatusBadGateway,
-			fmt.Sprintf("useGpuCliqueLabel=true but no matching nodes found; check label %q and annotation %q",
-				topology.KeyNvidiaGPUClique, topology.KeyNodeInstance))
+			fmt.Sprintf("useGpuCliqueLabel=true but no matching nodes found; check label %q and annotation %q. "+
+				"Scanned %d node(s): %d without a SLURM node mapping (no Ready slurmd pod), %d missing the %q label, %d with the label but missing the %q annotation%s",
+				topology.KeyNvidiaGPUClique, topology.KeyNodeInstance,
+				totalNodes, noSlurmName, noCliqueLabel, topology.KeyNvidiaGPUClique,
+				len(missingAnnotation), topology.KeyNodeInstance, formatMissingAnnotationNodes(missingAnnotation)))
 	}
 
 	if graph == nil {
@@ -300,6 +317,23 @@ func withGPUCliqueDomains(graph *topology.Graph, clusterNodes *clusterNodes) (*t
 	return graph, nil
 }
 
+// formatMissingAnnotationNodes renders the node names that carry the GPU clique
+// label but lack the node-data-broker-written instance annotation. The list is
+// capped so the error message stays bounded on large clusters.
+func formatMissingAnnotationNodes(nodes []string) string {
+	if len(nodes) == 0 {
+		return ""
+	}
+
+	const maxListed = 10
+	if len(nodes) <= maxListed {
+		return fmt.Sprintf(" (nodes missing annotation: %s)", strings.Join(nodes, ", "))
+	}
+
+	return fmt.Sprintf(" (nodes missing annotation: %s, and %d more)",
+		strings.Join(nodes[:maxListed], ", "), len(nodes)-maxListed)
+}
+
 func usesBlockTopology(cfg *translate.Config) bool {
 	if cfg == nil {
 		return false
diff --git a/pkg/engines/slinky/engine_test.go b/pkg/engines/slinky/engine_test.go
index bde0e743..8034773c 100644
--- a/pkg/engines/slinky/engine_test.go
+++ b/pkg/engines/slinky/engine_test.go
@@ -404,6 +404,42 @@ func TestWithGPUCliqueDomainsNoMatchingNodes(t *testing.T) {
 	got, httpErr := withGPUCliqueDomains(&topology.Graph{}, clusterNodes)
 	require.Nil(t, got)
 	require.ErrorContains(t, httpErr, "useGpuCliqueLabel=true but no matching nodes found")
+	// The node maps to a SLURM node but has no clique label.
+	require.ErrorContains(t, httpErr, "Scanned 1 node(s)")
+	require.ErrorContains(t, httpErr, fmt.Sprintf("1 missing the %q label", topology.KeyNvidiaGPUClique))
+}
+
+func TestWithGPUCliqueDomainsMissingBrokerAnnotation(t *testing.T) {
+	ctx := context.Background()
+	client := fake.NewSimpleClientset()
+
+	// Node has the GPU clique label but is missing the node-data-broker-written
+	// instance annotation - the exact scenario that produces the error in the field.
+	_, err := client.CoreV1().Nodes().Create(ctx, &corev1.Node{
+		ObjectMeta: metav1.ObjectMeta{
+			Name:   "k8s-node-0",
+			Labels: map[string]string{topology.KeyNvidiaGPUClique: "clique-a"},
+		},
+	}, metav1.CreateOptions{})
+	require.NoError(t, err)
+
+	_, err = client.CoreV1().Pods("test-ns").Create(ctx, makeReadySlurmdPod("pod-0", "k8s-node-0", "slurm-0"), metav1.CreateOptions{})
+	require.NoError(t, err)
+
+	eng := &SlinkyEngine{
+		client: client,
+		params: &Params{
+			Namespace:  "test-ns",
+			podListOpt: &metav1.ListOptions{LabelSelector: "app=slinky"},
+		},
+	}
+
+	clusterNodes, httpErr := eng.getClusterNodes(ctx)
+	require.Nil(t, httpErr)
+	got, httpErr := withGPUCliqueDomains(&topology.Graph{}, clusterNodes)
+	require.Nil(t, got)
+	require.ErrorContains(t, httpErr, fmt.Sprintf("1 with the label but missing the %q annotation", topology.KeyNodeInstance))
+	require.ErrorContains(t, httpErr, "nodes missing annotation: k8s-node-0")
 }
 
 func TestGenerateOutputUsesGPUCliqueDomains(t *testing.T) {