diff --git a/docs/swagger.yaml b/docs/swagger.yaml
index 638ce5cbc..d9a2a75e9 100644
--- a/docs/swagger.yaml
+++ b/docs/swagger.yaml
@@ -41,6 +41,32 @@ paths:
               $ref: '#/definitions/Search'
         '500':
           description: Unexpected internal errors.
+  /retag:
+    post:
+      summary: Retag an image
+      description: >
+        This endpoint tags an image with another tag in the same repo, or
+        to another repo or project.
+      parameters:
+        - name: request
+          in: body
+          description: reqeust to given source image and target image
+          required: true
+          schema:
+            $ref: '#/definitions/RetagReq'
+      tags:
+        - Products
+      responses:
+        '200':
+          description: Image retag successfully.
+        '400':
+          description: Invalid image values provided
+        '401':
+          description: User has no permission to the source project or destination project.
+        '404':
+          description: Project or repository not found.
+        '500':
+          description: Unexpected internal errors.
   /projects:
     get:
       summary: List projects
@@ -2966,6 +2992,15 @@ definitions:
         type: array
         items:
           $ref: '#/definitions/SearchResult'
+  RetagReq:
+    type: object
+    properties:
+      src_image:
+        description: Source image to be retagged, e.g. 'stage/app:v1.0'
+        type: string
+      dest_image:
+        description: Destination image tag to, e.g. 'product/app:v1.0'
+        type: string
   SearchRepository:
     type: object
     properties:
diff --git a/src/common/models/retag.go b/src/common/models/retag.go
index e0b1ab134..5ab9763f1 100644
--- a/src/common/models/retag.go
+++ b/src/common/models/retag.go
@@ -19,17 +19,21 @@ import (
 	"strings"
 )
 
+// RetagRequest gives the source image and target image of retag
 type RetagRequest struct {
-	SrcImage  string  `json:"src_image"`
-	DestImage string  `json:"dest_image"`
+	SrcImage  string `json:"src_image"`
+	DestImage string `json:"dest_image"`
 }
 
+// Image holds each part (project, repo, tag) of an image name
 type Image struct {
 	Project string
 	Repo    string
 	Tag     string
 }
 
+// ParseImage parses an image name such as 'library/app:v1.0' to a structure with
+// project, repo, and tag fields
 func ParseImage(image string) (*Image, error) {
 	repo := strings.SplitN(image, "/", 2)
 	if len(repo) < 2 {
@@ -38,10 +42,10 @@ func ParseImage(image string) (*Image, error) {
 	i := strings.SplitN(repo[1], ":", 2)
 	res := &Image{
 		Project: repo[0],
-		Repo:      i[0],
+		Repo:    i[0],
 	}
 	if len(i) == 2 {
 		res.Tag = i[1]
 	}
 	return res, nil
-}
\ No newline at end of file
+}
diff --git a/src/common/models/retag_test.go b/src/common/models/retag_test.go
index 5728dd859..f30d82ae2 100644
--- a/src/common/models/retag_test.go
+++ b/src/common/models/retag_test.go
@@ -15,23 +15,24 @@
 package models
 
 import (
-	"testing"
 	"reflect"
+	"testing"
+
 	"github.com/stretchr/testify/assert"
 )
 
 func TestParseImage(t *testing.T) {
 	cases := []struct {
-		Input  string
+		Input    string
 		Expected *Image
-		Valid  bool
-	} {
+		Valid    bool
+	}{
 		{
 			Input: "library/busybox",
 			Expected: &Image{
 				Project: "library",
-				Repo: "busybox",
-				Tag: "",
+				Repo:    "busybox",
+				Tag:     "",
 			},
 			Valid: true,
 		},
@@ -39,8 +40,8 @@ func TestParseImage(t *testing.T) {
 			Input: "library/busybox:v1.0",
 			Expected: &Image{
 				Project: "library",
-				Repo: "busybox",
-				Tag: "v1.0",
+				Repo:    "busybox",
+				Tag:     "v1.0",
 			},
 			Valid: true,
 		},
@@ -62,4 +63,4 @@ func TestParseImage(t *testing.T) {
 			}
 		}
 	}
-}
\ No newline at end of file
+}
diff --git a/src/common/utils/registry/repository.go b/src/common/utils/registry/repository.go
index 2f56d05dd..7e7a8a27f 100644
--- a/src/common/utils/registry/repository.go
+++ b/src/common/utils/registry/repository.go
@@ -258,6 +258,7 @@ func (r *Repository) DeleteManifest(digest string) error {
 	}
 }
 
+// MountBlob ...
 func (r *Repository) MountBlob(digest, from string) error {
 	req, err := http.NewRequest("POST", buildMountBlobURL(r.Endpoint.String(), r.Name, digest, from), nil)
 	req.Header.Set(http.CanonicalHeaderKey("Content-Length"), "0")
diff --git a/src/ui/api/retag.go b/src/ui/api/retag.go
index b0259dc9b..8334dda37 100644
--- a/src/ui/api/retag.go
+++ b/src/ui/api/retag.go
@@ -28,6 +28,7 @@ type RetagAPI struct {
 	BaseController
 }
 
+// Retag tags an image to another
 func (r *RetagAPI) Retag() {
 	if !r.SecurityCtx.IsAuthenticated() {
 		r.HandleUnauthorized()
diff --git a/src/ui/utils/retag.go b/src/ui/utils/retag.go
index 1abf43bb2..0394f0408 100644
--- a/src/ui/utils/retag.go
+++ b/src/ui/utils/retag.go
@@ -25,13 +25,15 @@ import (
 	"github.com/docker/distribution/manifest/schema2"
 )
 
+// Retag tags an image to another
 func Retag(srcImage, destImage *models.Image) error {
+	isSameRepo := getRepoName(srcImage) == getRepoName(destImage)
 	srcClient, err := NewRepositoryClientForUI("harbor-ui", getRepoName(srcImage))
 	if err != nil {
 		return err
 	}
 	destClient := srcClient
-	if getRepoName(srcImage) != getRepoName(destImage) {
+	if !isSameRepo {
 		destClient, err = NewRepositoryClientForUI("harbor-ui", getRepoName(destImage))
 		if err != nil {
 			return err
@@ -70,7 +72,7 @@ func Retag(srcImage, destImage *models.Image) error {
 		return nil
 	}
 
-	if getRepoName(srcImage) != getRepoName(destImage) {
+	if !isSameRepo {
 		for _, descriptor := range manifest.References() {
 			err := destClient.MountBlob(descriptor.Digest.String(), srcClient.Name)
 			if err != nil {