diff --git a/sf-writer/README.md b/sf-writer/README.md
index 1300b11..606129e 100644
--- a/sf-writer/README.md
+++ b/sf-writer/README.md
@@ -1,5 +1,8 @@
 # sf-writer
 
+sf-writer reads the binary buffer from disk, assembled the images and writes 
+them down in HDF5 format.
+
 ## Data request ranges
 
 Data request ranges are composed of: