diff --git a/util/cairo-sphinx/sphinx.c b/util/cairo-sphinx/sphinx.c
index 7bc1c505d..3a6c04c35 100644
--- a/util/cairo-sphinx/sphinx.c
+++ b/util/cairo-sphinx/sphinx.c
@@ -1,3 +1,11 @@
+/*
+ * The intention for sphinx is for detection of rendering errors inside
+ * applications by simultaneously rendering on to the target device and on
+ * an image surface and comparing the two. If it found a discrepancy, it
+ * would then dump the trace that reproduces the error. (Then apply
+ * delta-debugging to reduce that down to a minimal trace.)
+ */
+
 #ifdef HAVE_CONFIG_H
 #include "config.h"
 #endif