diff --git a/api/types/filters/parse.go b/api/types/filters/parse.go
index 4c5aff6616..cd7ad92e79 100644
--- a/api/types/filters/parse.go
+++ b/api/types/filters/parse.go
@@ -36,6 +36,7 @@ func NewArgs(initialArgs ...KeyValuePair) Args {
 	return args
 }
 
+// Keys returns all the keys in list of Args
 func (args Args) Keys() []string {
 	keys := make([]string, 0, len(args.fields))
 	for k := range args.fields {
diff --git a/daemon/config/builder.go b/daemon/config/builder.go
index 8d2d12b671..07eb5ced20 100644
--- a/daemon/config/builder.go
+++ b/daemon/config/builder.go
@@ -16,8 +16,10 @@ type BuilderGCRule struct {
 	KeepStorage string          `json:",omitempty"`
 }
 
+// BuilderGCFilter contains garbage-collection filter rules for a BuildKit builder
 type BuilderGCFilter filters.Args
 
+// MarshalJSON returns a JSON byte representation of the BuilderGCFilter
 func (x *BuilderGCFilter) MarshalJSON() ([]byte, error) {
 	f := filters.Args(*x)
 	keys := f.Keys()
@@ -32,6 +34,7 @@ func (x *BuilderGCFilter) MarshalJSON() ([]byte, error) {
 	return json.Marshal(arr)
 }
 
+// UnmarshalJSON fills the BuilderGCFilter values structure from JSON input
 func (x *BuilderGCFilter) UnmarshalJSON(data []byte) error {
 	var arr []string
 	f := filters.NewArgs()