diff --git a/content/index.md b/content/index.md
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--- a/content/index.md
+++ b/content/index.md
@@ -48,6 +48,10 @@ Stuff I've made!
 
 2025\. homeworlds pyramids, made from die-cut paper! [link](/pyramids/)
 
+### Graph Zendo
+
+2020\. a modded version of the excellent Zendo by Kory Heath. my version uses flowcharts. you can play this at work. [link](/zendo/)
+
 ### Braceless Javascript
 2018\. a couple of short programs written in browser JavaScript, with the special restriction that I can't use any instructions that require curly braces, like 'if' or 'for'. instead, I replace these instructions with ternaries and lambdas, which makes this a functional programming exercise!
 
diff --git a/content/zendo.md b/content/zendo.md
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--- a/content/zendo.md
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@@ -27,4 +27,22 @@ flowcharts! how could we possibly communicate if we didn't have some sort of dig
 
 ## graph zendo rules summary
 
-TODO: finish this section
+<img src="/a/graph-zendo-sample.png" alt="four graphs" title="four graphs">
+
+If you've played Zendo before, here's the change notes:
+
+- a **koan** is a **graph** which is a collection of nodes and arrows.
+
+- a **node** is a triangle, circle, or square.
+
+- an **arrow** is a one-way path that begins at a node and ends at a node. arrows are considered to be shapeless; the rule cannot refer to "bent arrows" for instance.
+
+- each graph should also be given a number for reference. the number is not part of the graph.
+
+- there are no turns, and there are no guessing tokens. this is because in an office setting it can be difficult and unfun to keep track of whose turn it is and how many tokens people have. instead:
+
+  - a player may draw a new graph at any time. a 'dot' under a graph indicates that it is ready to be judged. the puzzle master should circle or cross out this dot.
+
+  - a player may attempt to solve at any time. they should raise their hand and wait for the puzzle master to call on them.
+
+_TODO: write a version of these rules for people who haven't played zendo before_
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