diff --git a/internal/topdata/class_spellbooks.go b/internal/topdata/class_spellbooks.go
index 97fd09c..790a0a2 100644
--- a/internal/topdata/class_spellbooks.go
+++ b/internal/topdata/class_spellbooks.go
@@ -47,6 +47,9 @@ func validateClassSpellbooks(dataDir string, report *ValidationReport) {
 	}
 	_, diagnostics := classSpellbookPlans(dataDir, collected)
 	report.Diagnostics = append(report.Diagnostics, diagnostics...)
+	if len(diagnostics) == 0 {
+		warnSpellModulesForManagedSpellbookColumns(dataDir, collected, report)
+	}
 }
 
 func collectSpellbookValidationDatasets(dataDir string) ([]nativeCollectedDataset, error) {
@@ -187,6 +190,81 @@ func classSpellbookPlans(dataDir string, collected []nativeCollectedDataset) ([]
 	return plans, diagnostics
 }
 
+func warnSpellModulesForManagedSpellbookColumns(dataDir string, collected []nativeCollectedDataset, report *ValidationReport) {
+	plans, diagnostics := classSpellbookPlans(dataDir, collected)
+	if len(diagnostics) > 0 || len(plans) == 0 {
+		return
+	}
+	managed := map[string]classSpellbookPlan{}
+	for _, plan := range plans {
+		managed[strings.ToLower(plan.Column)] = plan
+	}
+	paths, err := collectModulePaths(filepath.Join(dataDir, "spells", "modules"))
+	if err != nil {
+		report.Diagnostics = append(report.Diagnostics, Diagnostic{Severity: SeverityError, Path: dataDir, Message: fmt.Sprintf("collect spell modules for spellbook warnings: %v", err)})
+		return
+	}
+	for _, path := range paths {
+		obj, err := loadJSONObject(path)
+		if err != nil {
+			continue
+		}
+		warnSpellbookManagedColumnsInValue(dataDir, path, obj["entries"], managed, report)
+		warnSpellbookManagedColumnsInValue(dataDir, path, obj["overrides"], managed, report)
+		warnSpellbookManagedColumnsInValue(dataDir, path, obj["rows"], managed, report)
+	}
+}
+
+func warnSpellbookManagedColumnsInValue(dataDir, path string, value any, managed map[string]classSpellbookPlan, report *ValidationReport) {
+	switch typed := value.(type) {
+	case map[string]any:
+		for _, key := range sortedKeys(typed) {
+			row, ok := typed[key].(map[string]any)
+			if !ok {
+				continue
+			}
+			warnSpellbookManagedColumnsInRow(dataDir, path, row, managed, report)
+		}
+	case []any:
+		for _, raw := range typed {
+			row, ok := raw.(map[string]any)
+			if !ok {
+				continue
+			}
+			warnSpellbookManagedColumnsInRow(dataDir, path, row, managed, report)
+		}
+	}
+}
+
+func warnSpellbookManagedColumnsInRow(dataDir, path string, row map[string]any, managed map[string]classSpellbookPlan, report *ValidationReport) {
+	for field, value := range row {
+		plan, ok := managed[strings.ToLower(field)]
+		if !ok || isNullLikeValue(value) {
+			continue
+		}
+		spellbookPath := displayTopdataPath(dataDir, plan.Spec.Path)
+		report.Diagnostics = append(report.Diagnostics, Diagnostic{
+			Severity: SeverityWarning,
+			Path:     path,
+			Message: fmt.Sprintf(
+				"spell module authors class spell column %q managed by class spellbook %s; use %s instead",
+				plan.Column,
+				spellbookPath,
+				spellbookPath,
+			),
+		})
+	}
+}
+
+func displayTopdataPath(dataDir, path string) string {
+	topdataDir := filepath.Dir(dataDir)
+	rel, err := filepath.Rel(filepath.Dir(topdataDir), path)
+	if err != nil {
+		return filepath.ToSlash(path)
+	}
+	return filepath.ToSlash(rel)
+}
+
 func loadClassSpellbookSpecs(dir string) ([]classSpellbookSpec, []Diagnostic) {
 	paths, err := collectModulePaths(dir)
 	if err != nil {
diff --git a/internal/topdata/topdata_test.go b/internal/topdata/topdata_test.go
index cc3aece..bc555da 100644
--- a/internal/topdata/topdata_test.go
+++ b/internal/topdata/topdata_test.go
@@ -13626,6 +13626,41 @@ func TestValidateProjectRejectsInvalidClassSpellbooks(t *testing.T) {
 	}
 }
 
+func TestValidateProjectWarnsWhenSpellModuleAuthorsManagedSpellbookColumn(t *testing.T) {
+	root := testProjectRoot(t)
+	writeMinimalSpellbookProject(t, root)
+	mkdirAll(t, filepath.Join(root, "topdata", "data", "spells", "modules"))
+	writeFile(t, filepath.Join(root, "topdata", "data", "classes", "spellbooks", "bard.json"), `{
+  "key": "classes/spellbooks:bard",
+  "class": "classes:bard",
+  "levels": {
+    "0": ["spells:flare"]
+  }
+}`+"\n")
+	writeFile(t, filepath.Join(root, "topdata", "data", "spells", "modules", "direct_class_column.json"), `{
+  "columns": ["Sorcerer"],
+  "entries": {
+    "spells:module_spell": {
+      "Label": "ModuleSpell",
+      "Bard": 1,
+      "Sorcerer": 1
+    }
+  }
+}`+"\n")
+
+	report := ValidateProject(testProject(root))
+	if report.HasErrors() {
+		t.Fatalf("expected warning-only validation result, got errors:\n%s", diagnosticsText(report.Diagnostics))
+	}
+	text := diagnosticsText(report.Diagnostics)
+	if !strings.Contains(text, `spell module authors class spell column "Bard" managed by class spellbook`) {
+		t.Fatalf("expected managed Bard column warning, got:\n%s", text)
+	}
+	if !strings.Contains(text, `use topdata/data/classes/spellbooks/bard.json instead`) {
+		t.Fatalf("expected warning to point at spellbook file, got:\n%s", text)
+	}
+}
+
 func TestValidateProjectDoesNotRewritePlainDatasetLockfile(t *testing.T) {
 	root := testProjectRoot(t)
 	mkdirAll(t, filepath.Join(root, "topdata", "data", "ruleset"))