diff --git a/internal/confgen/confgen.go b/internal/confgen/confgen.go
index ea7190fb..e4957b85 100644
--- a/internal/confgen/confgen.go
+++ b/internal/confgen/confgen.go
@@ -23,7 +23,6 @@ import (
 	"google.golang.org/protobuf/reflect/protoreflect"
 	"google.golang.org/protobuf/reflect/protoregistry"
 	"google.golang.org/protobuf/types/descriptorpb"
-	"google.golang.org/protobuf/types/dynamicpb"
 )
 
 // Error collection limits at each level.
@@ -98,9 +97,7 @@ func (gen *Generator) GenAll() error {
 		return err
 	}
 	// Create a validator with extension type resolver for custom predefined rules.
-	gen.validator, err = protovalidate.New(
-		protovalidate.WithExtensionTypeResolver(dynamicpb.NewTypes(prFiles)),
-	)
+	gen.validator, err = NewValidator(prFiles)
 	if err != nil {
 		return err
 	}
@@ -126,9 +123,7 @@ func (gen *Generator) GenWorkbook(bookSpecifiers ...string) error {
 		return err
 	}
 	// Create a validator with extension type resolver for custom predefined rules.
-	gen.validator, err = protovalidate.New(
-		protovalidate.WithExtensionTypeResolver(dynamicpb.NewTypes(prFiles)),
-	)
+	gen.validator, err = NewValidator(prFiles)
 	if err != nil {
 		return err
 	}
diff --git a/internal/confgen/util.go b/internal/confgen/util.go
index 8bb3308d..1afa7fde 100644
--- a/internal/confgen/util.go
+++ b/internal/confgen/util.go
@@ -26,6 +26,7 @@ import (
 	"google.golang.org/protobuf/reflect/protoreflect"
 	"google.golang.org/protobuf/reflect/protoregistry"
 	"google.golang.org/protobuf/types/descriptorpb"
+	"google.golang.org/protobuf/types/dynamicpb"
 )
 
 var fieldOptionsPool *sync.Pool
@@ -314,9 +315,19 @@ func parseOutputFormats(msg proto.Message, opt *options.ConfOutputOption) []form
 	return format.OutputFormats
 }
 
-// validate validates a proto message using the provided validator. Each violation
+// NewValidator creates a protovalidate validator whose extension type resolver
+// is built from prFiles, so custom predefined rules can be recognized. It is
+// shared by both the confgen (generate) and load (checker) paths to keep
+// validation behavior consistent.
+func NewValidator(prFiles *protoregistry.Files) (protovalidate.Validator, error) {
+	return protovalidate.New(
+		protovalidate.WithExtensionTypeResolver(dynamicpb.NewTypes(prFiles)),
+	)
+}
+
+// Validate validates a proto message using the provided validator. Each violation
 // is wrapped as an E2027 error and all violations are joined together.
-func validate(msg proto.Message, validator protovalidate.Validator) error {
+func Validate(msg proto.Message, validator protovalidate.Validator) error {
 	err := validator.Validate(msg)
 	if err == nil {
 		return nil
@@ -342,7 +353,7 @@ func validate(msg proto.Message, validator protovalidate.Validator) error {
 
 // storeMessage stores a message to one or multiple file formats.
 func storeMessage(msg proto.Message, name, locationName, outputDir string, opt *options.ConfOutputOption, validator protovalidate.Validator) error {
-	if err := validate(msg, validator); err != nil {
+	if err := Validate(msg, validator); err != nil {
 		return err
 	}
 	outputDir = filepath.Join(outputDir, opt.Subdir)
diff --git a/internal/confgen/util_test.go b/internal/confgen/util_test.go
index 287a8f0e..fadcd6d1 100644
--- a/internal/confgen/util_test.go
+++ b/internal/confgen/util_test.go
@@ -412,7 +412,7 @@ func Test_validate(t *testing.T) {
 			if err != nil {
 				t.Fatalf("failed to create validator: %v", err)
 			}
-			err = validate(tt.args.msg, validator)
+			err = Validate(tt.args.msg, validator)
 			if (err != nil) != tt.wantErr {
 				t.Errorf("validate() error = %v, wantErr %v", err, tt.wantErr)
 				return
diff --git a/load/load.go b/load/load.go
index 8bd840f8..e9fa22c1 100644
--- a/load/load.go
+++ b/load/load.go
@@ -8,6 +8,7 @@ import (
 	"context"
 	"path/filepath"
 
+	"buf.build/go/protovalidate"
 	"github.com/tableauio/tableau/format"
 	"github.com/tableauio/tableau/internal/confgen"
 	"github.com/tableauio/tableau/internal/importer"
@@ -24,6 +25,16 @@ import (
 
 // LoadMessagerInDir loads message's content in the given dir, based on format and messager options.
 func LoadMessagerInDir(msg proto.Message, dir string, fmt format.Format, opts *MessagerOptions) error {
+	if err := loadMessagerInDir(msg, dir, fmt, opts); err != nil {
+		return err
+	}
+	// protovalidate the fully-assembled message. protovalidate operates on the
+	// final in-memory protobuf, so both input (excel/csv/xml/yaml) and output
+	// (json/binpb/txtpb) formats get the same coverage as confgen's storeMessage.
+	return confgen.Validate(msg, protovalidate.GlobalValidator)
+}
+
+func loadMessagerInDir(msg proto.Message, dir string, fmt format.Format, opts *MessagerOptions) error {
 	if format.IsInputFormat(fmt) {
 		return loadOrigin(msg, dir, opts)
 	}
diff --git a/load/load_test.go b/load/load_test.go
index 6a6e4561..4fc65119 100644
--- a/load/load_test.go
+++ b/load/load_test.go
@@ -299,6 +299,28 @@ func TestLoadJSON_E0002(t *testing.T) {
 	t.Logf("error: %s", xerrors.NewDesc(err).String())
 }
 
+// TestLoadProtovalidate guards the protovalidate step in LoadMessagerInDir:
+// protovalidate operates on the final in-memory message, so it must run for
+// both input (excel/csv/xml/yaml) and output (json/binpb/txtpb) formats.
+// ValidateConf constrains Name to max_len:10, and each fixture supplies a
+// longer value, so a fully-assembled message must surface an E2027 violation.
+// This catches regressions if the confgen.Validate call is ever dropped.
+func TestLoadProtovalidate(t *testing.T) {
+	t.Run("input-format-csv", func(t *testing.T) {
+		err := LoadMessagerInDir(&unittestpb.ValidateConf{}, "../testdata/", format.CSV, &MessagerOptions{})
+		require.Error(t, err)
+		require.ErrorIs(t, err, xerrors.ErrE2027)
+		t.Logf("error: %s", xerrors.NewDesc(err).String())
+	})
+
+	t.Run("output-format-json", func(t *testing.T) {
+		err := LoadMessagerInDir(&unittestpb.ValidateConf{}, "../testdata/unittest/conf/", format.JSON, &MessagerOptions{})
+		require.Error(t, err)
+		require.ErrorIs(t, err, xerrors.ErrE2027)
+		t.Logf("error: %s", xerrors.NewDesc(err).String())
+	})
+}
+
 func TestLoadWithPatch(t *testing.T) {
 	type args struct {
 		msg     proto.Message
diff --git a/testdata/unittest/Unittest#ValidateConf.csv b/testdata/unittest/Unittest#ValidateConf.csv
new file mode 100644
index 00000000..f6868ec0
--- /dev/null
+++ b/testdata/unittest/Unittest#ValidateConf.csv
@@ -0,0 +1,4 @@
+ID,Name,Tag,Prop
+uint32,string,"[]string","map<string, int32>"
+Conf ID,Conf name,Tags,Props
+0,this name is too long,"a,b","x:1"
diff --git a/testdata/unittest/conf/ValidateConf.json b/testdata/unittest/conf/ValidateConf.json
new file mode 100644
index 00000000..0dee462d
--- /dev/null
+++ b/testdata/unittest/conf/ValidateConf.json
@@ -0,0 +1,4 @@
+{
+    "id": 0,
+    "name": "this name is too long"
+}