diff --git a/GB_key_mask_t.md b/GB_key_mask_t.md
index d41c3fb..49c3f9e 100644
--- a/GB_key_mask_t.md
+++ b/GB_key_mask_t.md
@@ -19,4 +19,9 @@ In `joypad.h`
 
 ## Description
 
-TBD
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+An enum representing each of the 8 buttons of a Game Boy as a mask value. Multiple values can be combine with `|` and used with functions such as [[GB_set_key_mask]].
+
+## See Also
+
+* [[GB_set_key_mask]]
+* [[GB_set_key_mask_for_player]]
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