diff --git a/internal/radio/song.go b/internal/radio/song.go
index 5e3fb5c..0730a27 100644
--- a/internal/radio/song.go
+++ b/internal/radio/song.go
@@ -6,8 +6,8 @@ import (
 	"time"
 )
 
-// Song stores artist and title of a song, a timestamp of when it started, and
-// a maximum number of listeners.
+// Song stores artist and title of a song, a timestamp of when it started, its
+// duration, and a maximum number of listeners.
 type Song struct {
 	Artist       string
 	Title        string
@@ -16,10 +16,13 @@ type Song struct {
 	StartAt      time.Time
 }
 
+// ArtistTitle returns a concatination of an artist and a title with a hyphen
+// between then.
 func (s *Song) ArtistTitle() string {
 	return s.Artist + " - " + s.Title
 }
 
+// DurationString returns song's duration as a string formatted as [H:]M:SS.
 func (s *Song) DurationString() string {
 	if s.Duration.Hours() >= 1 {
 		return time.UnixMilli(s.Duration.Milliseconds()).Format("3:4:05")
@@ -31,7 +34,7 @@ func (s *Song) MarshalJSON() ([]byte, error) {
 	return json.Marshal(&struct {
 		Artist       string `json:"artist"`
 		Title        string `json:"title"`
-		DurationMill int64  `json:"duration_milliseconds"`
+		DurationMill int64  `json:"duration_msec"`
 		Duration     string `json:"duration"`
 		MaxListeners int    `json:"listeners"`
 		StartAt      string `json:"start_at"`
@@ -45,27 +48,28 @@ func (s *Song) MarshalJSON() ([]byte, error) {
 }
 
 type SongList struct {
-	mut        sync.Mutex
-	current    Song
-	lastSongs  []Song
-	listMaxLen int
+	sync.Mutex
+	current   Song
+	lastSongs []Song
+	maxLen    int
 }
 
-func NewSongList(length int) *SongList {
-	return &SongList{listMaxLen: length, lastSongs: make([]Song, 0, length)}
+// NewSongList returns a new SongList with a maximal length set with maxLen.
+func NewSongList(maxLen int) *SongList {
+	return &SongList{maxLen: maxLen, lastSongs: make([]Song, 0, maxLen)}
 }
 
 // Add a new song that is currently playing and update a list.
 func (sl *SongList) Add(newSong Song) {
-	sl.mut.Lock()
-	defer sl.mut.Unlock()
+	sl.Lock()
+	defer sl.Unlock()
 
 	if sl.current.StartAt.Year() == 1 {
 		sl.current = newSong
 		return
 	}
 
-	if len(sl.lastSongs) == sl.listMaxLen {
+	if len(sl.lastSongs) == sl.maxLen {
 		sl.lastSongs = append(sl.lastSongs[1:], sl.current)
 	} else {
 		sl.lastSongs = append(sl.lastSongs, sl.current)
@@ -73,10 +77,10 @@ func (sl *SongList) Add(newSong Song) {
 	sl.current = newSong
 }
 
-// Current returns a current playing song.
+// Current returns a currently playing song.
 func (sl *SongList) Current() *Song {
-	sl.mut.Lock()
-	defer sl.mut.Unlock()
+	sl.Lock()
+	defer sl.Unlock()
 	if sl.current.StartAt.Year() == 1 {
 		return nil
 	}
@@ -85,11 +89,12 @@ func (sl *SongList) Current() *Song {
 
 // List returns a list of lastly played songs.
 func (sl *SongList) List() []Song {
-	sl.mut.Lock()
-	defer sl.mut.Unlock()
+	sl.Lock()
+	defer sl.Unlock()
 	return sl.lastSongs
 }
 
-func (sl *SongList) Len() int {
-	return sl.listMaxLen
+// MaxLen returns a maximal length of a list
+func (sl *SongList) MaxLen() int {
+	return sl.maxLen
 }