diff --git a/api/client-server/sync.yaml b/api/client-server/sync.yaml
index 4b399d07..eeed2e82 100644
--- a/api/client-server/sync.yaml
+++ b/api/client-server/sync.yaml
@@ -32,7 +32,13 @@ paths:
           name: filter
           type: string
           description: |-
-            The ID of a filter created using the filter API.
+            The ID of a filter created using the filter API or a filter JSON
+            object enocoded as a string. The server will detect whether it is
+            an ID or a JSON object by whether the first character is a ``"{"``
+            open brace. Passing the JSON inline is best suited to one off
+            requests. Creating a filter using the filter API is recommended for
+            clients that reuse the same filter multiple times, for example in
+            long poll requests.
           x-example: "66696p746572"
         - in: query
           name: since