diff --git a/tessellations/README.txt b/tessellations/README.txt
index 2aadc94c..ed6b3bd4 100644
--- a/tessellations/README.txt
+++ b/tessellations/README.txt
@@ -1 +1,2 @@
 go to https://github.com/zenorogue/tes-catalog for more!
+The format is explained in https://github.com/zenorogue/hyperrogue/blob/master/tessellations/sample/
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