diff --git a/core/mapping/jsonunmarshaler.go b/core/mapping/jsonunmarshaler.go
index bcad9993..523a8ca2 100644
--- a/core/mapping/jsonunmarshaler.go
+++ b/core/mapping/jsonunmarshaler.go
@@ -10,10 +10,12 @@ const jsonTagKey = "json"
 
 var jsonUnmarshaler = NewUnmarshaler(jsonTagKey)
 
+// UnmarshalJsonBytes unmarshals content into v.
 func UnmarshalJsonBytes(content []byte, v interface{}) error {
 	return unmarshalJsonBytes(content, v, jsonUnmarshaler)
 }
 
+// UnmarshalJsonReader unmarshals content from reader into v.
 func UnmarshalJsonReader(reader io.Reader, v interface{}) error {
 	return unmarshalJsonReader(reader, v, jsonUnmarshaler)
 }
diff --git a/core/mapping/jsonunmarshaler_test.go b/core/mapping/jsonunmarshaler_test.go
index fc561fd4..c98244c7 100644
--- a/core/mapping/jsonunmarshaler_test.go
+++ b/core/mapping/jsonunmarshaler_test.go
@@ -485,41 +485,41 @@ func TestUnmarshalBytesMap(t *testing.T) {
 func TestUnmarshalBytesMapStruct(t *testing.T) {
 	var c struct {
 		Persons map[string]struct {
-			Id   int
+			ID   int
 			Name string `json:"name,optional"`
 		}
 	}
-	content := []byte(`{"Persons": {"first": {"Id": 1, "name": "kevin"}}}`)
+	content := []byte(`{"Persons": {"first": {"ID": 1, "name": "kevin"}}}`)
 
 	assert.Nil(t, UnmarshalJsonBytes(content, &c))
 	assert.Equal(t, 1, len(c.Persons))
-	assert.Equal(t, 1, c.Persons["first"].Id)
+	assert.Equal(t, 1, c.Persons["first"].ID)
 	assert.Equal(t, "kevin", c.Persons["first"].Name)
 }
 
 func TestUnmarshalBytesMapStructPtr(t *testing.T) {
 	var c struct {
 		Persons map[string]*struct {
-			Id   int
+			ID   int
 			Name string `json:"name,optional"`
 		}
 	}
-	content := []byte(`{"Persons": {"first": {"Id": 1, "name": "kevin"}}}`)
+	content := []byte(`{"Persons": {"first": {"ID": 1, "name": "kevin"}}}`)
 
 	assert.Nil(t, UnmarshalJsonBytes(content, &c))
 	assert.Equal(t, 1, len(c.Persons))
-	assert.Equal(t, 1, c.Persons["first"].Id)
+	assert.Equal(t, 1, c.Persons["first"].ID)
 	assert.Equal(t, "kevin", c.Persons["first"].Name)
 }
 
 func TestUnmarshalBytesMapStructMissingPartial(t *testing.T) {
 	var c struct {
 		Persons map[string]*struct {
-			Id   int
+			ID   int
 			Name string
 		}
 	}
-	content := []byte(`{"Persons": {"first": {"Id": 1}}}`)
+	content := []byte(`{"Persons": {"first": {"ID": 1}}}`)
 
 	assert.NotNil(t, UnmarshalJsonBytes(content, &c))
 }
@@ -527,21 +527,21 @@ func TestUnmarshalBytesMapStructMissingPartial(t *testing.T) {
 func TestUnmarshalBytesMapStructOptional(t *testing.T) {
 	var c struct {
 		Persons map[string]*struct {
-			Id   int
+			ID   int
 			Name string `json:"name,optional"`
 		}
 	}
-	content := []byte(`{"Persons": {"first": {"Id": 1}}}`)
+	content := []byte(`{"Persons": {"first": {"ID": 1}}}`)
 
 	assert.Nil(t, UnmarshalJsonBytes(content, &c))
 	assert.Equal(t, 1, len(c.Persons))
-	assert.Equal(t, 1, c.Persons["first"].Id)
+	assert.Equal(t, 1, c.Persons["first"].ID)
 }
 
 func TestUnmarshalBytesMapEmptyStructSlice(t *testing.T) {
 	var c struct {
 		Persons map[string][]struct {
-			Id   int
+			ID   int
 			Name string `json:"name,optional"`
 		}
 	}
@@ -555,22 +555,22 @@ func TestUnmarshalBytesMapEmptyStructSlice(t *testing.T) {
 func TestUnmarshalBytesMapStructSlice(t *testing.T) {
 	var c struct {
 		Persons map[string][]struct {
-			Id   int
+			ID   int
 			Name string `json:"name,optional"`
 		}
 	}
-	content := []byte(`{"Persons": {"first": [{"Id": 1, "name": "kevin"}]}}`)
+	content := []byte(`{"Persons": {"first": [{"ID": 1, "name": "kevin"}]}}`)
 
 	assert.Nil(t, UnmarshalJsonBytes(content, &c))
 	assert.Equal(t, 1, len(c.Persons))
-	assert.Equal(t, 1, c.Persons["first"][0].Id)
+	assert.Equal(t, 1, c.Persons["first"][0].ID)
 	assert.Equal(t, "kevin", c.Persons["first"][0].Name)
 }
 
 func TestUnmarshalBytesMapEmptyStructPtrSlice(t *testing.T) {
 	var c struct {
 		Persons map[string][]*struct {
-			Id   int
+			ID   int
 			Name string `json:"name,optional"`
 		}
 	}
@@ -584,26 +584,26 @@ func TestUnmarshalBytesMapEmptyStructPtrSlice(t *testing.T) {
 func TestUnmarshalBytesMapStructPtrSlice(t *testing.T) {
 	var c struct {
 		Persons map[string][]*struct {
-			Id   int
+			ID   int
 			Name string `json:"name,optional"`
 		}
 	}
-	content := []byte(`{"Persons": {"first": [{"Id": 1, "name": "kevin"}]}}`)
+	content := []byte(`{"Persons": {"first": [{"ID": 1, "name": "kevin"}]}}`)
 
 	assert.Nil(t, UnmarshalJsonBytes(content, &c))
 	assert.Equal(t, 1, len(c.Persons))
-	assert.Equal(t, 1, c.Persons["first"][0].Id)
+	assert.Equal(t, 1, c.Persons["first"][0].ID)
 	assert.Equal(t, "kevin", c.Persons["first"][0].Name)
 }
 
 func TestUnmarshalBytesMapStructPtrSliceMissingPartial(t *testing.T) {
 	var c struct {
 		Persons map[string][]*struct {
-			Id   int
+			ID   int
 			Name string
 		}
 	}
-	content := []byte(`{"Persons": {"first": [{"Id": 1}]}}`)
+	content := []byte(`{"Persons": {"first": [{"ID": 1}]}}`)
 
 	assert.NotNil(t, UnmarshalJsonBytes(content, &c))
 }
@@ -611,15 +611,15 @@ func TestUnmarshalBytesMapStructPtrSliceMissingPartial(t *testing.T) {
 func TestUnmarshalBytesMapStructPtrSliceOptional(t *testing.T) {
 	var c struct {
 		Persons map[string][]*struct {
-			Id   int
+			ID   int
 			Name string `json:"name,optional"`
 		}
 	}
-	content := []byte(`{"Persons": {"first": [{"Id": 1}]}}`)
+	content := []byte(`{"Persons": {"first": [{"ID": 1}]}}`)
 
 	assert.Nil(t, UnmarshalJsonBytes(content, &c))
 	assert.Equal(t, 1, len(c.Persons))
-	assert.Equal(t, 1, c.Persons["first"][0].Id)
+	assert.Equal(t, 1, c.Persons["first"][0].ID)
 }
 
 func TestUnmarshalStructOptional(t *testing.T) {
diff --git a/core/mapping/unmarshaler.go b/core/mapping/unmarshaler.go
index 276b8f50..88371c7a 100644
--- a/core/mapping/unmarshaler.go
+++ b/core/mapping/unmarshaler.go
@@ -33,23 +33,27 @@ var (
 )
 
 type (
+	// A Unmarshaler is used to unmarshal with given tag key.
 	Unmarshaler struct {
 		key  string
 		opts unmarshalOptions
 	}
 
+	// UnmarshalOption defines the method to customize a Unmarshaler.
+	UnmarshalOption func(*unmarshalOptions)
+
 	unmarshalOptions struct {
 		fromString bool
 	}
 
-	keyCache        map[string][]string
-	UnmarshalOption func(*unmarshalOptions)
+	keyCache map[string][]string
 )
 
 func init() {
 	cacheKeys.Store(make(keyCache))
 }
 
+// NewUnmarshaler returns a Unmarshaler.
 func NewUnmarshaler(key string, opts ...UnmarshalOption) *Unmarshaler {
 	unmarshaler := Unmarshaler{
 		key: key,
@@ -62,14 +66,17 @@ func NewUnmarshaler(key string, opts ...UnmarshalOption) *Unmarshaler {
 	return &unmarshaler
 }
 
+// UnmarshalKey unmarshals m into v with tag key.
 func UnmarshalKey(m map[string]interface{}, v interface{}) error {
 	return keyUnmarshaler.Unmarshal(m, v)
 }
 
+// Unmarshal unmarshals m into v.
 func (u *Unmarshaler) Unmarshal(m map[string]interface{}, v interface{}) error {
 	return u.UnmarshalValuer(MapValuer(m), v)
 }
 
+// UnmarshalValuer unmarshals m into v.
 func (u *Unmarshaler) UnmarshalValuer(m Valuer, v interface{}) error {
 	return u.unmarshalWithFullName(m, v, "")
 }
@@ -590,6 +597,7 @@ func (u *Unmarshaler) parseOptionsWithContext(field reflect.StructField, m Value
 	return key, optsWithContext, nil
 }
 
+// WithStringValues customizes a Unmarshaler with number values from strings.
 func WithStringValues() UnmarshalOption {
 	return func(opt *unmarshalOptions) {
 		opt.fromString = true
diff --git a/core/mapping/unmarshaler_test.go b/core/mapping/unmarshaler_test.go
index b1cd1e53..65b4ea7e 100644
--- a/core/mapping/unmarshaler_test.go
+++ b/core/mapping/unmarshaler_test.go
@@ -754,13 +754,13 @@ func TestUnmarshalJsonNumberInt64(t *testing.T) {
 		strValue := strconv.FormatInt(intValue, 10)
 		var number = json.Number(strValue)
 		m := map[string]interface{}{
-			"Id": number,
+			"ID": number,
 		}
 		var v struct {
-			Id int64
+			ID int64
 		}
 		assert.Nil(t, UnmarshalKey(m, &v))
-		assert.Equal(t, intValue, v.Id)
+		assert.Equal(t, intValue, v.ID)
 	}
 }
 
@@ -770,13 +770,13 @@ func TestUnmarshalJsonNumberUint64(t *testing.T) {
 		strValue := strconv.FormatUint(intValue, 10)
 		var number = json.Number(strValue)
 		m := map[string]interface{}{
-			"Id": number,
+			"ID": number,
 		}
 		var v struct {
-			Id uint64
+			ID uint64
 		}
 		assert.Nil(t, UnmarshalKey(m, &v))
-		assert.Equal(t, intValue, v.Id)
+		assert.Equal(t, intValue, v.ID)
 	}
 }
 
@@ -786,15 +786,15 @@ func TestUnmarshalJsonNumberUint64Ptr(t *testing.T) {
 		strValue := strconv.FormatUint(intValue, 10)
 		var number = json.Number(strValue)
 		m := map[string]interface{}{
-			"Id": number,
+			"ID": number,
 		}
 		var v struct {
-			Id *uint64
+			ID *uint64
 		}
 		ast := assert.New(t)
 		ast.Nil(UnmarshalKey(m, &v))
-		ast.NotNil(v.Id)
-		ast.Equal(intValue, *v.Id)
+		ast.NotNil(v.ID)
+		ast.Equal(intValue, *v.ID)
 	}
 }
 
@@ -1061,38 +1061,38 @@ func TestUnmarshalWithOptionsAndSet(t *testing.T) {
 
 func TestUnmarshalNestedKey(t *testing.T) {
 	var c struct {
-		Id int `json:"Persons.first.Id"`
+		ID int `json:"Persons.first.ID"`
 	}
 	m := map[string]interface{}{
 		"Persons": map[string]interface{}{
 			"first": map[string]interface{}{
-				"Id": 1,
+				"ID": 1,
 			},
 		},
 	}
 
 	assert.Nil(t, NewUnmarshaler("json").Unmarshal(m, &c))
-	assert.Equal(t, 1, c.Id)
+	assert.Equal(t, 1, c.ID)
 }
 
 func TestUnmarhsalNestedKeyArray(t *testing.T) {
 	var c struct {
 		First []struct {
-			Id int
+			ID int
 		} `json:"Persons.first"`
 	}
 	m := map[string]interface{}{
 		"Persons": map[string]interface{}{
 			"first": []map[string]interface{}{
-				{"Id": 1},
-				{"Id": 2},
+				{"ID": 1},
+				{"ID": 2},
 			},
 		},
 	}
 
 	assert.Nil(t, NewUnmarshaler("json").Unmarshal(m, &c))
 	assert.Equal(t, 2, len(c.First))
-	assert.Equal(t, 1, c.First[0].Id)
+	assert.Equal(t, 1, c.First[0].ID)
 }
 
 func TestUnmarshalAnonymousOptionalRequiredProvided(t *testing.T) {
diff --git a/core/mapping/utils.go b/core/mapping/utils.go
index 6685ea93..813c93e9 100644
--- a/core/mapping/utils.go
+++ b/core/mapping/utils.go
@@ -45,6 +45,7 @@ type (
 	}
 )
 
+// Deref dereferences a type, if pointer type, returns its element type.
 func Deref(t reflect.Type) reflect.Type {
 	if t.Kind() == reflect.Ptr {
 		t = t.Elem()
@@ -53,6 +54,7 @@ func Deref(t reflect.Type) reflect.Type {
 	return t
 }
 
+// Repr returns the string representation of v.
 func Repr(v interface{}) string {
 	if v == nil {
 		return ""
@@ -72,6 +74,7 @@ func Repr(v interface{}) string {
 	return reprOfValue(val)
 }
 
+// ValidatePtr validates v if it's a valid pointer.
 func ValidatePtr(v *reflect.Value) error {
 	// sequence is very important, IsNil must be called after checking Kind() with reflect.Ptr,
 	// panic otherwise
diff --git a/core/mapping/valuer.go b/core/mapping/valuer.go
index 07dcdfcb..d1a0dfea 100644
--- a/core/mapping/valuer.go
+++ b/core/mapping/valuer.go
@@ -1,13 +1,17 @@
 package mapping
 
 type (
+	// A Valuer interface defines the way to get values from the underlying object with keys.
 	Valuer interface {
+		// Value gets the value associated with the given key.
 		Value(key string) (interface{}, bool)
 	}
 
+	// A MapValuer is a map that can use Value method to get values with given keys.
 	MapValuer map[string]interface{}
 )
 
+// Value gets the value associated with the given key from mv.
 func (mv MapValuer) Value(key string) (interface{}, bool) {
 	v, ok := mv[key]
 	return v, ok
diff --git a/core/mapping/yamlunmarshaler.go b/core/mapping/yamlunmarshaler.go
index c7f6947f..20a7bf6d 100644
--- a/core/mapping/yamlunmarshaler.go
+++ b/core/mapping/yamlunmarshaler.go
@@ -13,15 +13,18 @@ import (
 const yamlTagKey = "json"
 
 var (
+	// ErrUnsupportedType is an error that indicates the config format is not supported.
 	ErrUnsupportedType = errors.New("only map-like configs are suported")
 
 	yamlUnmarshaler = NewUnmarshaler(yamlTagKey)
 )
 
+// UnmarshalYamlBytes unmarshals content into v.
 func UnmarshalYamlBytes(content []byte, v interface{}) error {
 	return unmarshalYamlBytes(content, v, yamlUnmarshaler)
 }
 
+// UnmarshalYamlReader unmarshals content from reader into v.
 func UnmarshalYamlReader(reader io.Reader, v interface{}) error {
 	return unmarshalYamlReader(reader, v, yamlUnmarshaler)
 }
diff --git a/core/mapping/yamlunmarshaler_test.go b/core/mapping/yamlunmarshaler_test.go
index b9197c1d..d635fd74 100644
--- a/core/mapping/yamlunmarshaler_test.go
+++ b/core/mapping/yamlunmarshaler_test.go
@@ -502,49 +502,49 @@ func TestUnmarshalYamlBytesMap(t *testing.T) {
 func TestUnmarshalYamlBytesMapStruct(t *testing.T) {
 	var c struct {
 		Persons map[string]struct {
-			Id   int
+			ID   int
 			Name string `json:"name,optional"`
 		}
 	}
 	content := []byte(`Persons:
   first:
-    Id: 1
+    ID: 1
     name: kevin`)
 
 	assert.Nil(t, UnmarshalYamlBytes(content, &c))
 	assert.Equal(t, 1, len(c.Persons))
-	assert.Equal(t, 1, c.Persons["first"].Id)
+	assert.Equal(t, 1, c.Persons["first"].ID)
 	assert.Equal(t, "kevin", c.Persons["first"].Name)
 }
 
 func TestUnmarshalYamlBytesMapStructPtr(t *testing.T) {
 	var c struct {
 		Persons map[string]*struct {
-			Id   int
+			ID   int
 			Name string `json:"name,optional"`
 		}
 	}
 	content := []byte(`Persons:
   first:
-    Id: 1
+    ID: 1
     name: kevin`)
 
 	assert.Nil(t, UnmarshalYamlBytes(content, &c))
 	assert.Equal(t, 1, len(c.Persons))
-	assert.Equal(t, 1, c.Persons["first"].Id)
+	assert.Equal(t, 1, c.Persons["first"].ID)
 	assert.Equal(t, "kevin", c.Persons["first"].Name)
 }
 
 func TestUnmarshalYamlBytesMapStructMissingPartial(t *testing.T) {
 	var c struct {
 		Persons map[string]*struct {
-			Id   int
+			ID   int
 			Name string
 		}
 	}
 	content := []byte(`Persons:
   first:
-    Id: 1`)
+    ID: 1`)
 
 	assert.NotNil(t, UnmarshalYamlBytes(content, &c))
 }
@@ -552,41 +552,41 @@ func TestUnmarshalYamlBytesMapStructMissingPartial(t *testing.T) {
 func TestUnmarshalYamlBytesMapStructOptional(t *testing.T) {
 	var c struct {
 		Persons map[string]*struct {
-			Id   int
+			ID   int
 			Name string `json:"name,optional"`
 		}
 	}
 	content := []byte(`Persons:
   first:
-    Id: 1`)
+    ID: 1`)
 
 	assert.Nil(t, UnmarshalYamlBytes(content, &c))
 	assert.Equal(t, 1, len(c.Persons))
-	assert.Equal(t, 1, c.Persons["first"].Id)
+	assert.Equal(t, 1, c.Persons["first"].ID)
 }
 
 func TestUnmarshalYamlBytesMapStructSlice(t *testing.T) {
 	var c struct {
 		Persons map[string][]struct {
-			Id   int
+			ID   int
 			Name string `json:"name,optional"`
 		}
 	}
 	content := []byte(`Persons:
   first:
-  - Id: 1
+  - ID: 1
     name: kevin`)
 
 	assert.Nil(t, UnmarshalYamlBytes(content, &c))
 	assert.Equal(t, 1, len(c.Persons))
-	assert.Equal(t, 1, c.Persons["first"][0].Id)
+	assert.Equal(t, 1, c.Persons["first"][0].ID)
 	assert.Equal(t, "kevin", c.Persons["first"][0].Name)
 }
 
 func TestUnmarshalYamlBytesMapEmptyStructSlice(t *testing.T) {
 	var c struct {
 		Persons map[string][]struct {
-			Id   int
+			ID   int
 			Name string `json:"name,optional"`
 		}
 	}
@@ -601,25 +601,25 @@ func TestUnmarshalYamlBytesMapEmptyStructSlice(t *testing.T) {
 func TestUnmarshalYamlBytesMapStructPtrSlice(t *testing.T) {
 	var c struct {
 		Persons map[string][]*struct {
-			Id   int
+			ID   int
 			Name string `json:"name,optional"`
 		}
 	}
 	content := []byte(`Persons:
   first:
-  - Id: 1
+  - ID: 1
     name: kevin`)
 
 	assert.Nil(t, UnmarshalYamlBytes(content, &c))
 	assert.Equal(t, 1, len(c.Persons))
-	assert.Equal(t, 1, c.Persons["first"][0].Id)
+	assert.Equal(t, 1, c.Persons["first"][0].ID)
 	assert.Equal(t, "kevin", c.Persons["first"][0].Name)
 }
 
 func TestUnmarshalYamlBytesMapEmptyStructPtrSlice(t *testing.T) {
 	var c struct {
 		Persons map[string][]*struct {
-			Id   int
+			ID   int
 			Name string `json:"name,optional"`
 		}
 	}
@@ -634,13 +634,13 @@ func TestUnmarshalYamlBytesMapEmptyStructPtrSlice(t *testing.T) {
 func TestUnmarshalYamlBytesMapStructPtrSliceMissingPartial(t *testing.T) {
 	var c struct {
 		Persons map[string][]*struct {
-			Id   int
+			ID   int
 			Name string
 		}
 	}
 	content := []byte(`Persons:
   first:
-  - Id: 1`)
+  - ID: 1`)
 
 	assert.NotNil(t, UnmarshalYamlBytes(content, &c))
 }
@@ -648,17 +648,17 @@ func TestUnmarshalYamlBytesMapStructPtrSliceMissingPartial(t *testing.T) {
 func TestUnmarshalYamlBytesMapStructPtrSliceOptional(t *testing.T) {
 	var c struct {
 		Persons map[string][]*struct {
-			Id   int
+			ID   int
 			Name string `json:"name,optional"`
 		}
 	}
 	content := []byte(`Persons:
   first:
-  - Id: 1`)
+  - ID: 1`)
 
 	assert.Nil(t, UnmarshalYamlBytes(content, &c))
 	assert.Equal(t, 1, len(c.Persons))
-	assert.Equal(t, 1, c.Persons["first"][0].Id)
+	assert.Equal(t, 1, c.Persons["first"][0].ID)
 }
 
 func TestUnmarshalYamlStructOptional(t *testing.T) {