diff --git a/README.md b/README.md
index 4e9daf4..d5fea31 100644
--- a/README.md
+++ b/README.md
@@ -6,6 +6,12 @@ You can see it in action at
 
 ![Example tweet](Screen Shot 2019-12-13.png?raw=true "Example tweet")
 
+The bot uses the adsbexchange.com API to get aircraft data in
+realtime. It uses the Pelias front-end to OpenStreetMap and
+WhosOnFirst data to come up with some color description of the
+aircraft's location. It uses an embedded Chromium browser to take a
+screenshot of the aircraft on the adsbexchange.com "global radar
+view".
 
 ## Criteria for tweeting