diff --git a/gno.land/pkg/sdk/vm/errors.go b/gno.land/pkg/sdk/vm/errors.go
index 132d98b7ecd..0020e989eb6 100644
--- a/gno.land/pkg/sdk/vm/errors.go
+++ b/gno.land/pkg/sdk/vm/errors.go
@@ -20,7 +20,7 @@ type (
 	InvalidExprError    struct{ abciError }
 	TypeCheckError      struct {
 		abciError
-		Errors []string
+		Errors []string `json:"errors"`
 	}
 )
 
diff --git a/gno.land/pkg/sdk/vm/package_test.go b/gno.land/pkg/sdk/vm/package_test.go
new file mode 100644
index 00000000000..f19cc55aa20
--- /dev/null
+++ b/gno.land/pkg/sdk/vm/package_test.go
@@ -0,0 +1,49 @@
+package vm
+
+import (
+	"reflect"
+	"strings"
+	"testing"
+	"unicode"
+
+	"github.com/stretchr/testify/assert"
+)
+
+func TestJSONSnakeCase(t *testing.T) {
+	t.Parallel()
+	for _, typ := range Package.Types {
+		assertJSONSnakeCase(t, typ.Type)
+	}
+}
+
+func assertJSONSnakeCase(t *testing.T, typ reflect.Type) {
+	t.Helper()
+
+	switch typ.Kind() {
+	case reflect.Array, reflect.Slice, reflect.Pointer:
+		assertJSONSnakeCase(t, typ.Elem())
+	case reflect.Map:
+		assertJSONSnakeCase(t, typ.Key())
+		assertJSONSnakeCase(t, typ.Elem())
+	case reflect.Struct:
+		for i := 0; i < typ.NumField(); i++ {
+			fld := typ.Field(i)
+			if !fld.IsExported() {
+				continue
+			}
+			jt := fld.Tag.Get("json")
+			if jt == "" {
+				if fld.Anonymous {
+					assertJSONSnakeCase(t, fld.Type)
+					continue
+				}
+				t.Errorf("field %s.%s does not have a json tag but is exported", typ.Name(), fld.Name)
+				continue
+			}
+			has := strings.ContainsFunc(jt, unicode.IsUpper)
+			assert.False(t, has,
+				"field %s.%s contains uppercase symbols in json tag", typ.Name(), fld.Name)
+			assertJSONSnakeCase(t, fld.Type)
+		}
+	}
+}
diff --git a/tm2/pkg/std/memfile.go b/tm2/pkg/std/memfile.go
index ce73995a22a..01bc18c1487 100644
--- a/tm2/pkg/std/memfile.go
+++ b/tm2/pkg/std/memfile.go
@@ -8,8 +8,8 @@ import (
 )
 
 type MemFile struct {
-	Name string
-	Body string
+	Name string `json:"name" yaml:"name"`
+	Body string `json:"body" yaml:"body"`
 }
 
 // MemPackage represents the information and files of a package which will be
@@ -19,9 +19,9 @@ type MemFile struct {
 // NOTE: in the future, a MemPackage may represent
 // updates/additional-files for an existing package.
 type MemPackage struct {
-	Name  string // package name as declared by `package`
-	Path  string // import path
-	Files []*MemFile
+	Name  string     `json:"name" yaml:"name"` // package name as declared by `package`
+	Path  string     `json:"path" yaml:"path"` // import path
+	Files []*MemFile `json:"files" yaml:"files"`
 }
 
 func (mempkg *MemPackage) GetFile(name string) *MemFile {