diff --git a/tracker/tracker.go b/tracker/tracker.go
index 5ce7500c..701bacc0 100644
--- a/tracker/tracker.go
+++ b/tracker/tracker.go
@@ -15,12 +15,12 @@ type AnnounceRequest struct {
 	Event      AnnounceEvent
 	IPAddress  int32
 	Key        int32
-	NumWant    int32
+	NumWant    int32 // How many peer addresses are desired. -1 for default.
 	Port       int16
 }
 
 type AnnounceResponse struct {
-	Interval int32
+	Interval int32 // Minimum seconds the local peer should wait before next announce.
 	Leechers int32
 	Seeders  int32
 	Peers    []Peer
@@ -34,13 +34,14 @@ type Peer struct {
 }
 
 const (
-	None AnnounceEvent = iota
-	Completed
-	Started
-	Stopped
+	None      AnnounceEvent = iota
+	Completed               // The local peer just completed the torrent.
+	Started                 // The local peer has just resumed this torrent.
+	Stopped                 // The local peer is leaving the swarm.
 )
 
 type Client interface {
+	// Returns ErrNotConnected if Connect needs to be called.
 	Announce(*AnnounceRequest) (AnnounceResponse, error)
 	Connect() error
 }