--- a
+++ b/.env
@@ -0,0 +1,18 @@
+# This file defines environment variables we want to be set in development
+# environments. The Just command runner and VSCode's Python extension (but not
+# the terminal) should pick these up automatically, see:
+# https://github.com/casey/just#dotenv-load
+# https://code.visualstudio.com/docs/python/environments#_environment-variables
+#
+# You can load these manually in bash using something like:
+#
+#     set -o allexport; source .env; set +o allexport
+#
+
+# Disable hash randomisation. The kinds of DoS attacks hash seed randomisation
+# is designed to protect against don't apply to ehrQL, and having consistent
+# output makes debugging much easier
+PYTHONHASHSEED=0
+
+# Enable event level queries for testing purposes, but not yet in production
+EHRQL_ENABLE_EVENT_LEVEL_QUERIES=True