diff --git a/README.rst b/README.rst
index 7e8a9bd..bc04651 100644
--- a/README.rst
+++ b/README.rst
@@ -2,7 +2,8 @@ f3 - Fight Flash Fraud
 ======================
 
 f3 is a simple tool that tests flash cards capacity and performance to
-see if they live up to claimed specifications.
+see if they live up to claimed specifications. It fills the device with
+pseudorandom data and then checks if it returns the same on reading.
 
 F3 stands for Fight Flash Fraud, or Fight Fake Flash.