diff --git a/util/proto/marshal_test.go b/util/proto/marshal_test.go
index e565b7c..d5758f2 100644
--- a/util/proto/marshal_test.go
+++ b/util/proto/marshal_test.go
@@ -8,6 +8,7 @@ import (
 	"git.frostfs.info/TrueCloudLab/frostfs-api-go/v2/util/proto/test"
 	generated "git.frostfs.info/TrueCloudLab/frostfs-api-go/v2/util/proto/test/custom"
 	"github.com/stretchr/testify/require"
+	"google.golang.org/protobuf/encoding/protojson"
 	goproto "google.golang.org/protobuf/proto"
 )
 
@@ -51,33 +52,64 @@ func TestStableMarshalSingle(t *testing.T) {
 	}
 	for _, tc := range marshalCases {
 		t.Run(tc.name, func(t *testing.T) {
-			r := tc.input.MarshalProtobuf(nil)
-			require.Equal(t, len(r), tc.input.StableSize())
-			require.NotEmpty(t, r)
+			t.Run("proto", func(t *testing.T) {
+				r := tc.input.MarshalProtobuf(nil)
+				require.Equal(t, len(r), tc.input.StableSize())
+				require.NotEmpty(t, r)
 
-			var actual test.Primitives
-			require.NoError(t, goproto.Unmarshal(r, &actual))
+				var actual test.Primitives
+				require.NoError(t, goproto.Unmarshal(r, &actual))
 
-			var actualFrostfs generated.Primitives
-			require.NoError(t, actualFrostfs.UnmarshalProtobuf(r))
-			require.Equal(t, tc.input, &actualFrostfs)
+				var actualFrostfs generated.Primitives
+				require.NoError(t, actualFrostfs.UnmarshalProtobuf(r))
+				require.Equal(t, tc.input, &actualFrostfs)
 
-			// Compare each field directly, because proto-generated code has private fields.
-			require.Equal(t, tc.input.FieldA, actual.FieldA)
-			require.Equal(t, tc.input.FieldB, actual.FieldB)
-			require.Equal(t, tc.input.FieldC, actual.FieldC)
-			require.Equal(t, tc.input.FieldD, actual.FieldD)
-			require.Equal(t, tc.input.FieldE, actual.FieldE)
-			require.Equal(t, tc.input.FieldF, actual.FieldF)
-			require.Equal(t, tc.input.FieldG, actual.FieldG)
-			require.Equal(t, tc.input.FieldI, actual.FieldI)
-			require.Equal(t, tc.input.FieldJ, actual.FieldJ)
-			require.Equal(t, tc.input.FieldK, actual.FieldK)
-			require.EqualValues(t, tc.input.FieldH, actual.FieldH)
+				primitivesEqual(t, tc.input, &actual)
+			})
+			t.Run("json", func(t *testing.T) {
+				r, err := tc.input.MarshalJSON()
+				require.NoError(t, err)
+				require.NotEmpty(t, r)
+
+				var actual test.Primitives
+				require.NoError(t, protojson.Unmarshal(r, &actual))
+
+				var actualFrostfs generated.Primitives
+				require.NoError(t, actualFrostfs.UnmarshalJSON(r))
+				require.Equal(t, tc.input, &actualFrostfs)
+
+				primitivesEqual(t, tc.input, &actual)
+			})
 		})
 	}
 }
 
+func primitivesEqual(t *testing.T, a *generated.Primitives, b *test.Primitives) {
+	// Compare each field directly, because proto-generated code has private fields.
+	require.Equal(t, a.FieldA, b.FieldA)
+	require.Equal(t, a.FieldB, b.FieldB)
+	require.Equal(t, a.FieldC, b.FieldC)
+	require.Equal(t, a.FieldD, b.FieldD)
+	require.Equal(t, a.FieldE, b.FieldE)
+	require.Equal(t, a.FieldF, b.FieldF)
+	require.Equal(t, a.FieldG, b.FieldG)
+	require.Equal(t, a.FieldI, b.FieldI)
+	require.Equal(t, a.FieldJ, b.FieldJ)
+	require.Equal(t, a.FieldK, b.FieldK)
+	require.EqualValues(t, a.FieldH, b.FieldH)
+}
+
+func repPrimitivesEqual(t *testing.T, a *generated.RepPrimitives, b *test.RepPrimitives) {
+	// Compare each field directly, because proto-generated code has private fields.
+	require.Equal(t, a.FieldA, b.FieldA)
+	require.Equal(t, a.FieldB, b.FieldB)
+	require.Equal(t, a.FieldC, b.FieldC)
+	require.Equal(t, a.FieldD, b.FieldD)
+	require.Equal(t, a.FieldE, b.FieldE)
+	require.Equal(t, a.FieldF, b.FieldF)
+	require.Equal(t, a.FieldFu, b.FieldFu)
+}
+
 func randIntSlice[T protoInt](n int, includeZero bool) []T {
 	r := make([]T, n)
 	if n == 0 {
@@ -142,21 +174,24 @@ func TestStableMarshalRep(t *testing.T) {
 	}
 	for _, tc := range marshalCases {
 		t.Run(tc.name, func(t *testing.T) {
-			r := tc.input.MarshalProtobuf(nil)
-			require.Equal(t, len(r), tc.input.StableSize())
-			require.NotEmpty(t, r)
+			t.Run("proto", func(t *testing.T) {
+				r := tc.input.MarshalProtobuf(nil)
+				require.Equal(t, len(r), tc.input.StableSize())
+				require.NotEmpty(t, r)
 
-			var actual test.RepPrimitives
-			require.NoError(t, goproto.Unmarshal(r, &actual))
+				var actual test.RepPrimitives
+				require.NoError(t, goproto.Unmarshal(r, &actual))
+				repPrimitivesEqual(t, tc.input, &actual)
+			})
+			t.Run("json", func(t *testing.T) {
+				r, err := tc.input.MarshalJSON()
+				require.NoError(t, err)
+				require.NotEmpty(t, r)
 
-			// Compare each field directly, because proto-generated code has private fields.
-			require.Equal(t, tc.input.FieldA, actual.FieldA)
-			require.Equal(t, tc.input.FieldB, actual.FieldB)
-			require.Equal(t, tc.input.FieldC, actual.FieldC)
-			require.Equal(t, tc.input.FieldD, actual.FieldD)
-			require.Equal(t, tc.input.FieldE, actual.FieldE)
-			require.Equal(t, tc.input.FieldF, actual.FieldF)
-			require.Equal(t, tc.input.FieldFu, actual.FieldFu)
+				var actual test.RepPrimitives
+				require.NoError(t, protojson.Unmarshal(r, &actual))
+				repPrimitivesEqual(t, tc.input, &actual)
+			})
 		})
 	}
 }