diff --git a/internal/cmdrootfs/cmdrootfs.go b/internal/cmdrootfs/cmdrootfs.go
index 830a6d7..1e2b8cf 100644
--- a/internal/cmdrootfs/cmdrootfs.go
+++ b/internal/cmdrootfs/cmdrootfs.go
@@ -9,6 +9,7 @@ import (
 	"go.uber.org/multierr"
 )
 
+// CmdRootFS is "rootfs" command
 type CmdRootFS struct {
 	PositionalArgs struct {
 		Infile  goflags.Filename `long:"infile" description:"Input tarball"`
@@ -16,6 +17,7 @@ type CmdRootFS struct {
 	} `positional-args:"yes" required:"yes"`
 }
 
+// Execute executes CmdRootFS
 func (r *CmdRootFS) Execute(args []string) (err error) {
 	if len(args) != 0 {
 		return errors.New("too many args")
diff --git a/internal/tartest/tartest.go b/internal/tartest/tartest.go
index 6b1bb72..a4fc4ae 100644
--- a/internal/tartest/tartest.go
+++ b/internal/tartest/tartest.go
@@ -10,33 +10,39 @@ import (
 )
 
 type (
+	// Tarrer is an object that can tar itself to an archive
 	Tarrer interface {
 		Tar(*tar.Writer) error
 	}
 
+	// Tarball is a list of tarrables
 	Tarball []Tarrer
 
 	// Extractable is an empty interface for comparing extracted outputs in tests.
 	// Using that just to avoid the ugly `interface{}`.
 	Extractable interface{}
 
+	// Dir is a tarrable directory representation
 	Dir struct {
 		Name string
-		Uid  int
+		UID  int
 	}
 
+	// File is a tarrable file representation
 	File struct {
 		Name     string
-		Uid      int
+		UID      int
 		Contents *bytes.Buffer
 	}
 
+	// Hardlink is a representation of a hardlink
 	Hardlink struct {
 		Name string
-		Uid  int
+		UID  int
 	}
 )
 
+// Buffer returns a byte buffer
 func (tb Tarball) Buffer() *bytes.Buffer {
 	var buf bytes.Buffer
 	tw := tar.NewWriter(&buf)
@@ -47,16 +53,18 @@ func (tb Tarball) Buffer() *bytes.Buffer {
 	return &buf
 }
 
+// Tar tars the Dir
 func (d Dir) Tar(tw *tar.Writer) error {
 	hdr := &tar.Header{
 		Typeflag: tar.TypeDir,
 		Name:     d.Name,
 		Mode:     0644,
-		Uid:      d.Uid,
+		Uid:      d.UID,
 	}
 	return tw.WriteHeader(hdr)
 }
 
+// Tar tars the File
 func (f File) Tar(tw *tar.Writer) error {
 	var contents []byte
 	if f.Contents != nil {
@@ -66,7 +74,7 @@ func (f File) Tar(tw *tar.Writer) error {
 		Typeflag: tar.TypeReg,
 		Name:     f.Name,
 		Mode:     0644,
-		Uid:      f.Uid,
+		Uid:      f.UID,
 		Size:     int64(len(contents)),
 	}
 	if err := tw.WriteHeader(hdr); err != nil {
@@ -78,15 +86,17 @@ func (f File) Tar(tw *tar.Writer) error {
 	return nil
 }
 
+// Tar tars the Hardlink
 func (h Hardlink) Tar(tw *tar.Writer) error {
 	return tw.WriteHeader(&tar.Header{
 		Typeflag: tar.TypeLink,
 		Name:     h.Name,
 		Mode:     0644,
-		Uid:      h.Uid,
+		Uid:      h.UID,
 	})
 }
 
+// Extract extracts a tarball to a slice of extractables
 func Extract(t *testing.T, r io.Reader) []Extractable {
 	t.Helper()
 	ret := []Extractable{}
@@ -101,11 +111,11 @@ func Extract(t *testing.T, r io.Reader) []Extractable {
 		var elem Extractable
 		switch hdr.Typeflag {
 		case tar.TypeDir:
-			elem = Dir{Name: hdr.Name, Uid: hdr.Uid}
+			elem = Dir{Name: hdr.Name, UID: hdr.Uid}
 		case tar.TypeLink:
 			elem = Hardlink{Name: hdr.Name}
 		case tar.TypeReg:
-			f := File{Name: hdr.Name, Uid: hdr.Uid}
+			f := File{Name: hdr.Name, UID: hdr.Uid}
 			if hdr.Size > 0 {
 				var buf bytes.Buffer
 				io.Copy(&buf, tr)
diff --git a/rootfs/rootfs_test.go b/rootfs/rootfs_test.go
index b596e63..f445289 100644
--- a/rootfs/rootfs_test.go
+++ b/rootfs/rootfs_test.go
@@ -21,16 +21,16 @@ type (
 
 func TestRootFS(t *testing.T) {
 	layer0 := tarball{
-		dir{Name: "/", Uid: 0},
-		file{Name: "/file", Uid: 0, Contents: bytes.NewBufferString("from 0")},
+		dir{Name: "/", UID: 0},
+		file{Name: "/file", UID: 0, Contents: bytes.NewBufferString("from 0")},
 	}
 
 	layer1 := tarball{
-		file{Name: "/file", Uid: 1, Contents: bytes.NewBufferString("from 1")},
+		file{Name: "/file", UID: 1, Contents: bytes.NewBufferString("from 1")},
 	}
 
 	layer2 := tarball{
-		dir{Name: "/", Uid: 2},
+		dir{Name: "/", UID: 2},
 	}
 
 	tests := []struct {
@@ -57,8 +57,8 @@ func TestRootFS(t *testing.T) {
 				manifest{"layer0/layer.tar", "layer1/layer.tar"},
 			},
 			want: []extractable{
-				dir{Name: "/", Uid: 0},
-				file{Name: "/file", Uid: 1, Contents: bytes.NewBufferString("from 1")},
+				dir{Name: "/", UID: 0},
+				file{Name: "/file", UID: 1, Contents: bytes.NewBufferString("from 1")},
 			},
 		},
 		{
@@ -85,9 +85,9 @@ func TestRootFS(t *testing.T) {
 				manifest{"layer0/layer.tar", "layer1/layer.tar", "layer2/layer.tar"},
 			},
 			want: []extractable{
-				dir{Name: "/", Uid: 0},
-				file{Name: "/file", Uid: 1, Contents: bytes.NewBufferString("from 1")},
-				dir{Name: "/", Uid: 2},
+				dir{Name: "/", UID: 0},
+				file{Name: "/file", UID: 1, Contents: bytes.NewBufferString("from 1")},
+				dir{Name: "/", UID: 2},
 			},
 		},
 		{