diff --git a/mtglib/init.go b/mtglib/init.go
index 34e9e4e..9f3ba08 100644
--- a/mtglib/init.go
+++ b/mtglib/init.go
@@ -129,7 +129,15 @@ type EventStream interface {
 	Send(context.Context, Event)
 }
 
+// TimeAttackDetector is an abstraction that checks a time, taken from
+// the faketls client hello message. This timestamp is encoded into
+// client-generated random bytes and can be extracted after some client
+// hello verification.
+//
+// This is mostly to prevent replay attacks.
 type TimeAttackDetector interface {
+	// Valid returns an error if timestamp is invalid or should not be
+	// accepted.
 	Valid(time.Time) error
 }
 
diff --git a/timeattack/detector.go b/timeattack/detector.go
index ba70d3b..4ed1179 100644
--- a/timeattack/detector.go
+++ b/timeattack/detector.go
@@ -29,6 +29,9 @@ func (d detector) Valid(then time.Time) error {
 	return nil
 }
 
+// NewDetector returns a new TimeAttackDetector which validates that
+// timestamp belongs to intervar [X-duration, X+duration], so a small
+// timeshift is acceptable.
 func NewDetector(duration time.Duration) mtglib.TimeAttackDetector {
 	return detector{
 		Duration: duration,
diff --git a/timeattack/init.go b/timeattack/init.go
index 5bf3ab4..1c66919 100644
--- a/timeattack/init.go
+++ b/timeattack/init.go
@@ -1,7 +1,10 @@
+// TimeAttack has implementation of mtglib.TimeAttackDetector>
 package timeattack
 
 import "time"
 
-const (
-	DefaultDuration = 5 * time.Second
-)
+// DefaultDuration is a default duration when timestamps are acceptable.
+//
+// It means that all timestamps which are X-DefaultDuration <= X <=
+// X+DefaultDuration are fine.
+const DefaultDuration = 5 * time.Second
diff --git a/timeattack/noop.go b/timeattack/noop.go
index 43537c5..e3827b8 100644
--- a/timeattack/noop.go
+++ b/timeattack/noop.go
@@ -10,6 +10,7 @@ type noop struct{}
 
 func (n noop) Valid(_ time.Time) error { return nil }
 
+// NewNoop returns TimeAttackDetector which accepts all timestamps.
 func NewNoop() mtglib.TimeAttackDetector {
 	return noop{}
 }