diff --git a/models/interfaces.go b/models/interfaces.go
index 9ebecea..2db0687 100644
--- a/models/interfaces.go
+++ b/models/interfaces.go
@@ -27,23 +27,37 @@ import (
 	"github.com/spf13/viper"
 )
 
+// A listen service backend.
+// All listen services must implement this interface.
 type Backend interface {
 	FromConfig(config *viper.Viper) Backend
 }
 
+// Must be implemented by services supporting the export of listens.
 type ListensExport interface {
+	// Returns a list of all listens newer then oldestTimestamp.
+	// The returned list of listens is supposed to be ordered by the
+	// Listen.ListenedAt timestamp, with the oldest entry first.
 	ExportListens(oldestTimestamp time.Time) ([]Listen, error)
 }
 
+// Must be implemented by services supporting the import of listens.
 type ListensImport interface {
+	// Imports the given list of listens.
 	ImportListens(listens []Listen, oldestTimestamp time.Time) (ImportResult, error)
 }
 
+// Must be implemented by services supporting the export of loves.
 type LovesExport interface {
+	// Returns a list of all loves newer then oldestTimestamp.
+	// The returned list of listens is supposed to be ordered by the
+	// Love.Created timestamp, with the oldest entry first.
 	ExportLoves(oldestTimestamp time.Time) ([]Love, error)
 }
 
+// Must be implemented by services supporting the import of loves.
 type LovesImport interface {
+	// Imports the given list of loves.
 	ImportLoves(loves []Love, oldestTimestamp time.Time) (ImportResult, error)
 }