diff --git a/internal/job/types.go b/internal/job/types.go
index 45923f2de..f37a0bb5f 100644
--- a/internal/job/types.go
+++ b/internal/job/types.go
@@ -18,7 +18,7 @@ package job
 
 type PreheatRequest struct {
 	URL     string            `json:"url" validate:"required,url"`
-	Tag     string            `json:"tag" validate:"required"`
+	Tag     string            `json:"tag" validate:"omitempty"`
 	Digest  string            `json:"digest" validate:"omitempty"`
 	Filter  string            `json:"filter" validate:"omitempty"`
 	Headers map[string]string `json:"headers" validate:"omitempty"`
diff --git a/manager/job/preheat.go b/manager/job/preheat.go
index 618c3aa99..7100abed7 100644
--- a/manager/job/preheat.go
+++ b/manager/job/preheat.go
@@ -47,11 +47,15 @@ var tracer = otel.Tracer("manager")
 type PreheatType string
 
 const (
+	// PreheatImageType is image type of preheat job.
 	PreheatImageType PreheatType = "image"
-	PreheatFileType  PreheatType = "file"
+
+	// PreheatFileType is file type of preheat job.
+	PreheatFileType PreheatType = "file"
 )
 
 const (
+	// Timeout is the default timeout of http client.
 	timeout = 1 * time.Minute
 )