diff --git a/services/thumbnails/pkg/preprocessor/preprocessor.go b/services/thumbnails/pkg/preprocessor/preprocessor.go
index e03e52e5da..b8949dc953 100644
--- a/services/thumbnails/pkg/preprocessor/preprocessor.go
+++ b/services/thumbnails/pkg/preprocessor/preprocessor.go
@@ -4,7 +4,6 @@ import (
 	"archive/zip"
 	"bufio"
 	"bytes"
-	"fmt"
 	"image"
 	"image/draw"
 	"image/gif"
@@ -22,12 +21,15 @@ import (
 	"github.com/dhowden/tag"
 )
 
+// FileConverter is the interface for the file converter
 type FileConverter interface {
 	Convert(r io.Reader) (interface{}, error)
 }
 
+// ImageDecoder is a converter for the image file
 type ImageDecoder struct{}
 
+// Convert reads the image file and returns the thumbnail image
 func (i ImageDecoder) Convert(r io.Reader) (interface{}, error) {
 	img, err := imaging.Decode(r, imaging.AutoOrientation(true))
 	if err != nil {
@@ -36,8 +38,10 @@ func (i ImageDecoder) Convert(r io.Reader) (interface{}, error) {
 	return img, nil
 }
 
+// GifDecoder is a converter for the gif file
 type GifDecoder struct{}
 
+// Convert reads the gif file and returns the thumbnail image
 func (i GifDecoder) Convert(r io.Reader) (interface{}, error) {
 	img, err := gif.DecodeAll(r)
 	if err != nil {
@@ -46,8 +50,10 @@ func (i GifDecoder) Convert(r io.Reader) (interface{}, error) {
 	return img, nil
 }
 
+// GgsDecoder is a converter for the geogebra slides file
 type GgsDecoder struct{}
 
+// Convert reads the ggs file and returns the thumbnail image
 func (g GgsDecoder) Convert(r io.Reader) (interface{}, error) {
 	geogebraThumbnail := "_slide0/geogebra_thumbnail.png"
 	var buf bytes.Buffer
@@ -73,11 +79,13 @@ func (g GgsDecoder) Convert(r io.Reader) (interface{}, error) {
 			return img, nil
 		}
 	}
-	return nil, errors.New(fmt.Sprintf("%s not found", geogebraThumbnail))
+	return nil, errors.Errorf("%s not found", geogebraThumbnail)
 }
 
+// AudioDecoder is a converter for the audio file
 type AudioDecoder struct{}
 
+// Convert reads the audio file and extracts the thumbnail image from the id3 tag
 func (i AudioDecoder) Convert(r io.Reader) (interface{}, error) {
 	b, err := io.ReadAll(r)
 	if err != nil {
@@ -101,10 +109,12 @@ func (i AudioDecoder) Convert(r io.Reader) (interface{}, error) {
 	return converter.Convert(bytes.NewReader(picture.Data))
 }
 
+// TxtToImageConverter is a converter for the text file
 type TxtToImageConverter struct {
 	fontLoader *FontLoader
 }
 
+// Convert reads the text file and renders it into a thumbnail image
 func (t TxtToImageConverter) Convert(r io.Reader) (interface{}, error) {
 	img := image.NewRGBA(image.Rect(0, 0, 640, 480))
 
@@ -221,6 +231,7 @@ func drawWord(canvas *font.Drawer, word string, minX, maxX, incY, maxY fixed.Int
 	}
 }
 
+// ForType returns the converter for the specified mimeType
 func ForType(mimeType string, opts map[string]interface{}) FileConverter {
 	// We can ignore the error here because we parse it in IsMimeTypeSupported before and if it fails
 	// return the service call. So we should only get here when the mimeType parses fine.