diff --git a/packages/chord/src/delta/README.md b/packages/chord/src/delta/README.md
index d69e99095..b3ea667cb 100644
--- a/packages/chord/src/delta/README.md
+++ b/packages/chord/src/delta/README.md
@@ -3,6 +3,10 @@
 Chord Delta synchronizes one mutable JSON value from an authoritative producer
 to an ordered replica. It is available from `@earendil-works/chord/delta`.
 
+A change is represented by an `Op`: a small JSON tuple that replaces the root,
+sets or deletes a value, updates a string, or splices an array. `flush()` returns
+`Op[]`; `apply()` replays those operations on a replica.
+
 ```ts
 import { apply, track } from "@earendil-works/chord/delta";