diff --git a/core/search/tree.go b/core/search/tree.go
index e6c4d796..c49754b9 100644
--- a/core/search/tree.go
+++ b/core/search/tree.go
@@ -1,6 +1,9 @@
 package search
 
-import "errors"
+import (
+	"errors"
+	"fmt"
+)
 
 const (
 	colon = ':'
@@ -8,16 +11,16 @@ const (
 )
 
 var (
-	// ErrDupItem means adding duplicated item.
-	ErrDupItem = errors.New("duplicated item")
-	// ErrDupSlash means item is started with more than one slash.
-	ErrDupSlash = errors.New("duplicated slash")
-	// ErrEmptyItem means adding empty item.
-	ErrEmptyItem = errors.New("empty item")
-	// ErrInvalidState means search tree is in an invalid state.
-	ErrInvalidState = errors.New("search tree is in an invalid state")
-	// ErrNotFromRoot means path is not starting with slash.
-	ErrNotFromRoot = errors.New("path should start with /")
+	// errDupItem means adding duplicated item.
+	errDupItem = errors.New("duplicated item")
+	// errDupSlash means item is started with more than one slash.
+	errDupSlash = errors.New("duplicated slash")
+	// errEmptyItem means adding empty item.
+	errEmptyItem = errors.New("empty item")
+	// errInvalidState means search tree is in an invalid state.
+	errInvalidState = errors.New("search tree is in an invalid state")
+	// errNotFromRoot means path is not starting with slash.
+	errNotFromRoot = errors.New("path should start with /")
 
 	// NotFound is used to hold the not found result.
 	NotFound Result
@@ -58,14 +61,22 @@ func NewTree() *Tree {
 // Add adds item to associate with route.
 func (t *Tree) Add(route string, item interface{}) error {
 	if len(route) == 0 || route[0] != slash {
-		return ErrNotFromRoot
+		return errNotFromRoot
 	}
 
 	if item == nil {
-		return ErrEmptyItem
+		return errEmptyItem
 	}
 
-	return add(t.root, route[1:], item)
+	err := add(t.root, route[1:], item)
+	switch err {
+	case errDupItem:
+		return duplicatedItem(route)
+	case errDupSlash:
+		return duplicatedSlash(route)
+	default:
+		return err
+	}
 }
 
 // Search searches item that associates with given route.
@@ -141,7 +152,7 @@ func (nd *node) getChildren(route string) map[string]*node {
 func add(nd *node, route string, item interface{}) error {
 	if len(route) == 0 {
 		if nd.item != nil {
-			return ErrDupItem
+			return errDupItem
 		}
 
 		nd.item = item
@@ -149,7 +160,7 @@ func add(nd *node, route string, item interface{}) error {
 	}
 
 	if route[0] == slash {
-		return ErrDupSlash
+		return errDupSlash
 	}
 
 	for i := range route {
@@ -161,7 +172,7 @@ func add(nd *node, route string, item interface{}) error {
 					return add(child, route[i+1:], item)
 				}
 
-				return ErrInvalidState
+				return errInvalidState
 			}
 
 			child := newNode(nil)
@@ -173,7 +184,7 @@ func add(nd *node, route string, item interface{}) error {
 	children := nd.getChildren(route)
 	if child, ok := children[route]; ok {
 		if child.item != nil {
-			return ErrDupItem
+			return errDupItem
 		}
 
 		child.item = item
@@ -192,6 +203,14 @@ func addParam(result *Result, k, v string) {
 	result.Params[k] = v
 }
 
+func duplicatedItem(item string) error {
+	return fmt.Errorf("duplicated item for %s", item)
+}
+
+func duplicatedSlash(item string) error {
+	return fmt.Errorf("duplicated slash for %s", item)
+}
+
 func match(pat, token string) innerResult {
 	if pat[0] == colon {
 		return innerResult{
diff --git a/core/search/tree_test.go b/core/search/tree_test.go
index 763d3abf..b7166e5a 100644
--- a/core/search/tree_test.go
+++ b/core/search/tree_test.go
@@ -151,9 +151,9 @@ func TestAddDuplicate(t *testing.T) {
 	err := tree.Add("/a/b", 1)
 	assert.Nil(t, err)
 	err = tree.Add("/a/b", 2)
-	assert.Equal(t, ErrDupItem, err)
+	assert.Error(t, errDupItem, err)
 	err = tree.Add("/a/b/", 2)
-	assert.Equal(t, ErrDupItem, err)
+	assert.Error(t, errDupItem, err)
 }
 
 func TestPlain(t *testing.T) {
@@ -169,19 +169,19 @@ func TestPlain(t *testing.T) {
 func TestSearchWithDoubleSlashes(t *testing.T) {
 	tree := NewTree()
 	err := tree.Add("//a", 1)
-	assert.Error(t, ErrDupSlash, err)
+	assert.Error(t, errDupSlash, err)
 }
 
 func TestSearchInvalidRoute(t *testing.T) {
 	tree := NewTree()
 	err := tree.Add("", 1)
-	assert.Equal(t, ErrNotFromRoot, err)
+	assert.Equal(t, errNotFromRoot, err)
 	err = tree.Add("bad", 1)
-	assert.Equal(t, ErrNotFromRoot, err)
+	assert.Equal(t, errNotFromRoot, err)
 }
 
 func TestSearchInvalidItem(t *testing.T) {
 	tree := NewTree()
 	err := tree.Add("/", nil)
-	assert.Equal(t, ErrEmptyItem, err)
+	assert.Equal(t, errEmptyItem, err)
 }