diff --git a/openapi.go b/openapi.go
index 670a3ef..94e014f 100644
--- a/openapi.go
+++ b/openapi.go
@@ -122,7 +122,6 @@ func (sb *SpecBuilder) buildPaths(groups []RouteGroup) map[string]any {
 			operation := map[string]any{
 				"summary":     rd.Summary,
 				"description": rd.Description,
-				"tags":        resolvedOperationTags(g, rd),
 				"operationId": operationID(method, fullPath, operationIDs),
 				"security": []any{
 					map[string]any{
@@ -131,6 +130,9 @@ func (sb *SpecBuilder) buildPaths(groups []RouteGroup) map[string]any {
 				},
 				"responses": operationResponses(method, rd.Response),
 			}
+			if tags := resolvedOperationTags(g, rd); len(tags) > 0 {
+				operation["tags"] = tags
+			}
 
 			if params := pathParameters(fullPath); len(params) > 0 {
 				operation["parameters"] = params
@@ -341,8 +343,8 @@ func (sb *SpecBuilder) buildTags(groups []RouteGroup) []map[string]any {
 	seen := map[string]bool{"system": true}
 
 	for _, g := range groups {
-		name := g.Name()
-		if !seen[name] {
+		name := strings.TrimSpace(g.Name())
+		if name != "" && !seen[name] {
 			tags = append(tags, map[string]any{
 				"name":        name,
 				"description": name + " endpoints",
@@ -357,6 +359,7 @@ func (sb *SpecBuilder) buildTags(groups []RouteGroup) []map[string]any {
 
 		for _, rd := range dg.Describe() {
 			for _, tag := range rd.Tags {
+				tag = strings.TrimSpace(tag)
 				if tag == "" || seen[tag] {
 					continue
 				}
@@ -491,16 +494,42 @@ func mergeOperationParameters(existing any, explicit []map[string]any) []map[str
 // stable fallback derived from the group's name when the route omits tags.
 func resolvedOperationTags(g RouteGroup, rd RouteDescription) []string {
 	if len(rd.Tags) > 0 {
-		return rd.Tags
+		return cleanTags(rd.Tags)
 	}
 
-	if name := g.Name(); name != "" {
+	if name := strings.TrimSpace(g.Name()); name != "" {
 		return []string{name}
 	}
 
 	return nil
 }
 
+// cleanTags trims whitespace and removes empty or duplicate tags while
+// preserving the first occurrence of each name.
+func cleanTags(tags []string) []string {
+	if len(tags) == 0 {
+		return nil
+	}
+
+	cleaned := make([]string, 0, len(tags))
+	seen := make(map[string]struct{}, len(tags))
+	for _, tag := range tags {
+		tag = strings.TrimSpace(tag)
+		if tag == "" {
+			continue
+		}
+		if _, ok := seen[tag]; ok {
+			continue
+		}
+		seen[tag] = struct{}{}
+		cleaned = append(cleaned, tag)
+	}
+	if len(cleaned) == 0 {
+		return nil
+	}
+	return cleaned
+}
+
 // envelopeSchema wraps a data schema in the standard Response[T] envelope.
 func envelopeSchema(dataSchema map[string]any) map[string]any {
 	properties := map[string]any{
diff --git a/openapi_test.go b/openapi_test.go
index 5b55ef6..b0f737b 100644
--- a/openapi_test.go
+++ b/openapi_test.go
@@ -833,6 +833,64 @@ func TestSpecBuilder_Good_DefaultTagsFromGroupName(t *testing.T) {
 	}
 }
 
+func TestSpecBuilder_Good_BlankTagsAreIgnored(t *testing.T) {
+	sb := &api.SpecBuilder{
+		Title:   "Test",
+		Version: "1.0.0",
+	}
+
+	group := &specStubGroup{
+		name:     "   ",
+		basePath: "/api/blank",
+		descs: []api.RouteDescription{
+			{
+				Method:  "GET",
+				Path:    "/status",
+				Summary: "Check status",
+				Tags:    []string{"", "  ", "data", "data"},
+				Response: map[string]any{
+					"type": "object",
+				},
+			},
+		},
+	}
+
+	data, err := sb.Build([]api.RouteGroup{group})
+	if err != nil {
+		t.Fatalf("unexpected error: %v", err)
+	}
+
+	var spec map[string]any
+	if err := json.Unmarshal(data, &spec); err != nil {
+		t.Fatalf("invalid JSON: %v", err)
+	}
+
+	tags := spec["tags"].([]any)
+	var foundData bool
+	for _, raw := range tags {
+		tag := raw.(map[string]any)
+		name, _ := tag["name"].(string)
+		if name == "" {
+			t.Fatal("expected blank tag names to be ignored")
+		}
+		if name == "data" {
+			foundData = true
+		}
+	}
+	if !foundData {
+		t.Fatal("expected data tag to be retained")
+	}
+
+	op := spec["paths"].(map[string]any)["/api/blank/status"].(map[string]any)["get"].(map[string]any)
+	opTags, ok := op["tags"].([]any)
+	if !ok {
+		t.Fatalf("expected tags array, got %T", op["tags"])
+	}
+	if len(opTags) != 1 || opTags[0] != "data" {
+		t.Fatalf("expected operation tags to be cleaned to [data], got %v", opTags)
+	}
+}
+
 func TestSpecBuilder_Good_ToolBridgeIntegration(t *testing.T) {
 	gin.SetMode(gin.TestMode)