diff --git a/internal/codec/decoder_test.go b/internal/codec/decoder_test.go
index d4c9192..4e98623 100644
--- a/internal/codec/decoder_test.go
+++ b/internal/codec/decoder_test.go
@@ -83,7 +83,7 @@ func TestNewJSONStringDecoder(t *testing.T) {
 }
 
 func TestNewDecoder(t *testing.T) {
-	pbData, err := proto.Marshal(&TestUser{ Name: "pb", Uid: "15001", Group: "15005", Home: "/home/pb", State: "present" })
+	pbData, err := proto.Marshal(&TestPBUser{ Name: "pb", Uid: "15001", Group: "15005", Home: "/home/pb", State: "present" })
 	assert.Nil(t, err)
 	for _, v := range []struct{ reader io.Reader; format Format; expectedhome string } {
 		{ reader: strings.NewReader(`{
@@ -104,8 +104,31 @@ func TestNewDecoder(t *testing.T) {
 
 		decoder := NewDecoder(v.reader,  v.format)
 		assert.NotNil(t, decoder)
-		u := &TestUser{}
+		u := &TestPBUser{}
 		assert.Nil(t, decoder.Decode(u))
 		assert.Equal(t, v.expectedhome, u.Home )
 	}
 }
+
+func TestNewDecoderError(t *testing.T) {
+	pbData, err := proto.Marshal(&TestPBUser{ Name: "pb", Uid: "15001", Group: "15005", Home: "/home/pb", State: "present" })
+	assert.Nil(t, err)
+
+	decoder := NewDecoder(bytes.NewReader(pbData),  Format("foo"))
+	assert.Nil(t, decoder)
+}
+
+func TestNewStringDecoder(t *testing.T) {
+	jsonDoc := `{
+  "name": "testuser",
+  "uid": "12001",
+  "group": "12001",
+  "home": "/home/testuser",
+  "state": "present" }`
+	decoder := NewStringDecoder(jsonDoc, FormatJson)
+	assert.NotNil(t, decoder)
+	u := &TestUser{}
+	assert.Nil(t, decoder.Decode(u))
+	assert.Equal(t, "testuser", u.Name)
+	
+}
diff --git a/internal/codec/encoder.go b/internal/codec/encoder.go
index 80c09bd..e12e05c 100644
--- a/internal/codec/encoder.go
+++ b/internal/codec/encoder.go
@@ -9,8 +9,12 @@ _	"github.com/xeipuuv/gojsonschema"
 	"gopkg.in/yaml.v3"
 	"io"
 _	"log"
+	"errors"
+	"google.golang.org/protobuf/proto"
 )
 
+var ErrInvalidWriter error = errors.New("Invalid writer")
+
 type JSONEncoder json.Encoder
 
 type Encoder interface {
@@ -38,7 +42,29 @@ func NewYAMLEncoder(w io.Writer) Encoder {
 	return yaml.NewEncoder(w)
 }
 
+type ProtoEncoder struct {
+	writer io.Writer
+}
+
+func (p *ProtoEncoder) Encode(v any) (err error) {
+	var encoded []byte
+	encoded, err = proto.Marshal(v.(proto.Message))
+	if err != nil {
+		return
+	}
+
+	_, err = p.writer.Write(encoded)
+	return
+}
+
+func (p *ProtoEncoder) Close() error {
+	return nil
+}
+
 func NewProtoBufEncoder(w io.Writer) Encoder {
+	if w != nil {
+		return &ProtoEncoder{ writer: w }
+	}
 	return nil
 }
 
diff --git a/internal/codec/encoder_test.go b/internal/codec/encoder_test.go
index 4367db7..4fddea2 100644
--- a/internal/codec/encoder_test.go
+++ b/internal/codec/encoder_test.go
@@ -9,6 +9,9 @@ import (
 	"strings"
 	"testing"
 	"github.com/xeipuuv/gojsonschema"
+	"io"
+	"bytes"
+	"google.golang.org/protobuf/proto"
 )
 
 type TestFile struct {
@@ -56,3 +59,52 @@ schema:=`
 
 	assert.True(t, result.Valid())
 }
+
+func TestNewEncoder(t *testing.T) {
+
+	pb := &TestPBUser{ Name: "pb", Uid: "15001", Group: "15005", Home: "/home/pb", State: "present" }
+	jx := &TestUser{ Name: "jx", Uid: "17001", Group: "17005", Home: "/home/jx", State: "present" }
+
+	pbData, pbErr := proto.Marshal(pb)
+	assert.Nil(t, pbErr)
+
+	for _, v := range []struct{ writer io.Writer; testuser any; format Format; expected []byte} {
+		{ writer: &bytes.Buffer{}, testuser: jx, expected: []byte(`{"name":"jx","uid":"17001","group":"17005","home":"/home/jx","state":"present"}
+`), format: FormatJson },
+		{ writer: &bytes.Buffer{}, testuser: jx, expected: []byte(`name: jx
+uid: "17001"
+group: "17005"
+home: /home/jx
+state: present
+`), format: FormatYaml },
+		{ writer: &bytes.Buffer{}, testuser: pb, expected: pbData , format: FormatProtoBuf },
+	} {
+		encoder := NewEncoder(v.writer,  v.format)
+		assert.NotNil(t, encoder)
+		assert.Nil(t, encoder.Encode(v.testuser))
+		assert.Equal(t, string(v.expected), string(v.writer.(*bytes.Buffer).Bytes()))
+		assert.Equal(t, v.expected, v.writer.(*bytes.Buffer).Bytes())
+		assert.Nil(t, encoder.Close())
+	}
+}
+
+func TestNewEncoderError(t *testing.T) {
+	encoder := NewEncoder(&strings.Builder{}, Format("foo"))
+	assert.Nil(t, encoder)
+}
+
+func TestNewProtobufError(t *testing.T) {
+	encoder := NewProtoBufEncoder(nil)
+	assert.Nil(t, encoder)
+}
+
+/*
+func TestProtobufEncodeError(t *testing.T) {
+	buf := &bytes.Buffer{}
+	buf.Write([]byte("broken input"))
+
+	encoder := NewProtoBufEncoder(buf)
+	assert.NotNil(t, encoder)
+	assert.NotNil(t, encoder.Encode(&TestPBUser{}))
+}
+*/
diff --git a/internal/codec/testuser.pb.go b/internal/codec/testuser.pb.go
new file mode 100644
index 0000000..b4a04d9
--- /dev/null
+++ b/internal/codec/testuser.pb.go
@@ -0,0 +1,179 @@
+// Code generated by protoc-gen-go. DO NOT EDIT.
+// versions:
+// 	protoc-gen-go v1.34.2
+// 	protoc        v3.12.4
+// source: testuser.proto
+
+package codec
+
+import (
+	protoreflect "google.golang.org/protobuf/reflect/protoreflect"
+	protoimpl "google.golang.org/protobuf/runtime/protoimpl"
+	reflect "reflect"
+	sync "sync"
+)
+
+const (
+	// Verify that this generated code is sufficiently up-to-date.
+	_ = protoimpl.EnforceVersion(20 - protoimpl.MinVersion)
+	// Verify that runtime/protoimpl is sufficiently up-to-date.
+	_ = protoimpl.EnforceVersion(protoimpl.MaxVersion - 20)
+)
+
+type TestPBUser struct {
+	state         protoimpl.MessageState
+	sizeCache     protoimpl.SizeCache
+	unknownFields protoimpl.UnknownFields
+
+	Name  string `protobuf:"bytes,1,opt,name=Name,proto3" json:"Name,omitempty"`
+	Uid   string `protobuf:"bytes,2,opt,name=Uid,proto3" json:"Uid,omitempty"`
+	Group string `protobuf:"bytes,3,opt,name=Group,proto3" json:"Group,omitempty"`
+	Home  string `protobuf:"bytes,4,opt,name=Home,proto3" json:"Home,omitempty"`
+	State string `protobuf:"bytes,5,opt,name=State,proto3" json:"State,omitempty"`
+}
+
+func (x *TestPBUser) Reset() {
+	*x = TestPBUser{}
+	if protoimpl.UnsafeEnabled {
+		mi := &file_testuser_proto_msgTypes[0]
+		ms := protoimpl.X.MessageStateOf(protoimpl.Pointer(x))
+		ms.StoreMessageInfo(mi)
+	}
+}
+
+func (x *TestPBUser) String() string {
+	return protoimpl.X.MessageStringOf(x)
+}
+
+func (*TestPBUser) ProtoMessage() {}
+
+func (x *TestPBUser) ProtoReflect() protoreflect.Message {
+	mi := &file_testuser_proto_msgTypes[0]
+	if protoimpl.UnsafeEnabled && x != nil {
+		ms := protoimpl.X.MessageStateOf(protoimpl.Pointer(x))
+		if ms.LoadMessageInfo() == nil {
+			ms.StoreMessageInfo(mi)
+		}
+		return ms
+	}
+	return mi.MessageOf(x)
+}
+
+// Deprecated: Use TestPBUser.ProtoReflect.Descriptor instead.
+func (*TestPBUser) Descriptor() ([]byte, []int) {
+	return file_testuser_proto_rawDescGZIP(), []int{0}
+}
+
+func (x *TestPBUser) GetName() string {
+	if x != nil {
+		return x.Name
+	}
+	return ""
+}
+
+func (x *TestPBUser) GetUid() string {
+	if x != nil {
+		return x.Uid
+	}
+	return ""
+}
+
+func (x *TestPBUser) GetGroup() string {
+	if x != nil {
+		return x.Group
+	}
+	return ""
+}
+
+func (x *TestPBUser) GetHome() string {
+	if x != nil {
+		return x.Home
+	}
+	return ""
+}
+
+func (x *TestPBUser) GetState() string {
+	if x != nil {
+		return x.State
+	}
+	return ""
+}
+
+var File_testuser_proto protoreflect.FileDescriptor
+
+var file_testuser_proto_rawDesc = []byte{
+	0x0a, 0x0e, 0x74, 0x65, 0x73, 0x74, 0x75, 0x73, 0x65, 0x72, 0x2e, 0x70, 0x72, 0x6f, 0x74, 0x6f,
+	0x12, 0x05, 0x63, 0x6f, 0x64, 0x65, 0x63, 0x22, 0x72, 0x0a, 0x0a, 0x54, 0x65, 0x73, 0x74, 0x50,
+	0x42, 0x55, 0x73, 0x65, 0x72, 0x12, 0x12, 0x0a, 0x04, 0x4e, 0x61, 0x6d, 0x65, 0x18, 0x01, 0x20,
+	0x01, 0x28, 0x09, 0x52, 0x04, 0x4e, 0x61, 0x6d, 0x65, 0x12, 0x10, 0x0a, 0x03, 0x55, 0x69, 0x64,
+	0x18, 0x02, 0x20, 0x01, 0x28, 0x09, 0x52, 0x03, 0x55, 0x69, 0x64, 0x12, 0x14, 0x0a, 0x05, 0x47,
+	0x72, 0x6f, 0x75, 0x70, 0x18, 0x03, 0x20, 0x01, 0x28, 0x09, 0x52, 0x05, 0x47, 0x72, 0x6f, 0x75,
+	0x70, 0x12, 0x12, 0x0a, 0x04, 0x48, 0x6f, 0x6d, 0x65, 0x18, 0x04, 0x20, 0x01, 0x28, 0x09, 0x52,
+	0x04, 0x48, 0x6f, 0x6d, 0x65, 0x12, 0x14, 0x0a, 0x05, 0x53, 0x74, 0x61, 0x74, 0x65, 0x18, 0x05,
+	0x20, 0x01, 0x28, 0x09, 0x52, 0x05, 0x53, 0x74, 0x61, 0x74, 0x65, 0x42, 0x15, 0x5a, 0x13, 0x64,
+	0x65, 0x63, 0x6c, 0x2f, 0x69, 0x6e, 0x74, 0x65, 0x72, 0x6e, 0x61, 0x6c, 0x2f, 0x63, 0x6f, 0x64,
+	0x65, 0x63, 0x62, 0x06, 0x70, 0x72, 0x6f, 0x74, 0x6f, 0x33,
+}
+
+var (
+	file_testuser_proto_rawDescOnce sync.Once
+	file_testuser_proto_rawDescData = file_testuser_proto_rawDesc
+)
+
+func file_testuser_proto_rawDescGZIP() []byte {
+	file_testuser_proto_rawDescOnce.Do(func() {
+		file_testuser_proto_rawDescData = protoimpl.X.CompressGZIP(file_testuser_proto_rawDescData)
+	})
+	return file_testuser_proto_rawDescData
+}
+
+var file_testuser_proto_msgTypes = make([]protoimpl.MessageInfo, 1)
+var file_testuser_proto_goTypes = []any{
+	(*TestPBUser)(nil), // 0: codec.TestPBUser
+}
+var file_testuser_proto_depIdxs = []int32{
+	0, // [0:0] is the sub-list for method output_type
+	0, // [0:0] is the sub-list for method input_type
+	0, // [0:0] is the sub-list for extension type_name
+	0, // [0:0] is the sub-list for extension extendee
+	0, // [0:0] is the sub-list for field type_name
+}
+
+func init() { file_testuser_proto_init() }
+func file_testuser_proto_init() {
+	if File_testuser_proto != nil {
+		return
+	}
+	if !protoimpl.UnsafeEnabled {
+		file_testuser_proto_msgTypes[0].Exporter = func(v any, i int) any {
+			switch v := v.(*TestPBUser); i {
+			case 0:
+				return &v.state
+			case 1:
+				return &v.sizeCache
+			case 2:
+				return &v.unknownFields
+			default:
+				return nil
+			}
+		}
+	}
+	type x struct{}
+	out := protoimpl.TypeBuilder{
+		File: protoimpl.DescBuilder{
+			GoPackagePath: reflect.TypeOf(x{}).PkgPath(),
+			RawDescriptor: file_testuser_proto_rawDesc,
+			NumEnums:      0,
+			NumMessages:   1,
+			NumExtensions: 0,
+			NumServices:   0,
+		},
+		GoTypes:           file_testuser_proto_goTypes,
+		DependencyIndexes: file_testuser_proto_depIdxs,
+		MessageInfos:      file_testuser_proto_msgTypes,
+	}.Build()
+	File_testuser_proto = out.File
+	file_testuser_proto_rawDesc = nil
+	file_testuser_proto_goTypes = nil
+	file_testuser_proto_depIdxs = nil
+}
diff --git a/internal/codec/testuser.proto b/internal/codec/testuser.proto
new file mode 100644
index 0000000..dbcdf9b
--- /dev/null
+++ b/internal/codec/testuser.proto
@@ -0,0 +1,13 @@
+syntax = "proto3";
+package codec;
+option go_package = "decl/internal/codec";
+
+
+message TestPBUser {
+  string Name = 1;
+  string Uid = 2;
+  string Group = 3;
+	string Home = 4;
+	string State = 5;
+}
+
diff --git a/internal/codec/types.go b/internal/codec/types.go
index 232beb3..55e5f8e 100644
--- a/internal/codec/types.go
+++ b/internal/codec/types.go
@@ -11,6 +11,7 @@ import (
 )
 
 const (
+	FormatYml Format = "yml"
 	FormatYaml Format = "yaml"
 	FormatJson Format = "json"
 	FormatProtoBuf Format = "protobuf"
@@ -22,7 +23,7 @@ type Format string
 
 func (f *Format) Validate() error {
 	switch *f {
-	case FormatYaml, FormatJson, FormatProtoBuf:
+	case FormatYml, FormatYaml, FormatJson, FormatProtoBuf:
 		return nil
 	default:
 		return fmt.Errorf("%w: %s", ErrInvalidFormat, *f)
@@ -31,19 +32,21 @@ func (f *Format) Validate() error {
 
 func (f *Format) Set(value string) (err error) {
 	if err = (*Format)(&value).Validate(); err == nil {
-		*f = Format(value)
+		err = f.UnmarshalValue(value)
 	}
 	return
 }
 
 func (f *Format) UnmarshalValue(value string) error {
 	switch value {
+	case string(FormatYml):
+		*f = FormatYaml
 	case string(FormatYaml), string(FormatJson), string(FormatProtoBuf):
 		*f = Format(value)
-		return nil
 	default:
 		return ErrInvalidFormat
 	}
+	return nil
 }
 
 func (f *Format) UnmarshalJSON(data []byte) error {
diff --git a/internal/codec/types_test.go b/internal/codec/types_test.go
index 7d15461..017095d 100644
--- a/internal/codec/types_test.go
+++ b/internal/codec/types_test.go
@@ -7,6 +7,8 @@ _	"fmt"
 	"github.com/stretchr/testify/assert"
 _	"log"
 	"testing"
+	"strings"
+	"encoding/json"
 )
 
 type TestDec struct {
@@ -39,3 +41,37 @@ formattype: foo
 
 	assert.ErrorIs(t, ErrInvalidFormat, e)
 }
+
+func TestFormatValidate(t *testing.T) {
+	f := FormatYaml
+	assert.Nil(t, f.Validate())
+
+	var fail Format = Format("foo")
+	assert.ErrorIs(t, fail.Validate(), ErrInvalidFormat)
+
+	var testFormatSet Format
+	assert.Nil(t, testFormatSet.Set("yaml"))
+
+	assert.ErrorIs(t, testFormatSet.Set("yamlv3"), ErrInvalidFormat)
+}
+
+func TestFormatCodec(t *testing.T) {
+	var output map[string]Format = make(map[string]Format)
+	var writer strings.Builder
+	encoder := FormatYaml.Encoder(&writer)
+	assert.NotNil(t, encoder)
+
+	decoder := FormatYaml.Decoder(strings.NewReader("formattype: json"))
+	assert.Nil(t, decoder.Decode(output))
+	assert.Equal(t, FormatJson, output["formattype"])
+}
+
+func TestFormatUnmarshal(t *testing.T) {
+	var f Format 
+	assert.Nil(t, json.Unmarshal([]byte("\"yaml\""), &f))
+	assert.Equal(t, FormatYaml, f)
+	assert.NotNil(t, json.Unmarshal([]byte("\"yaml"), &f))
+
+	assert.Nil(t, json.Unmarshal([]byte("\"yml\""), &f))
+	assert.Equal(t, FormatYaml, f)
+}