diff --git a/api/client-server/content-repo.yaml b/api/client-server/content-repo.yaml
index a9a0c2f69..d596dbda3 100644
--- a/api/client-server/content-repo.yaml
+++ b/api/client-server/content-repo.yaml
@@ -340,6 +340,16 @@ paths:
   "/preview_url":
     get:
       summary: "Get information about a URL for a client"
+      description: |-
+        Get information about a URL for the client. Typically this is called when a
+        client sees a URL in a message and wants to render a preview for the user.
+
+        .. Note::
+          Clients should consider avoiding this endpoint for URLs posted in encrypted
+          rooms. Encrypted rooms often contain more sensitive information the users
+          do not want to share with the homeserver, and this can mean that the URLs
+          being shared should also not be shared with the homeserver.
+
       operationId: getUrlPreview
       produces: ["application/json"]
       security:
diff --git a/changelogs/client_server/newsfragments/2343.clarification b/changelogs/client_server/newsfragments/2343.clarification
new file mode 100644
index 000000000..5b16858b8
--- /dev/null
+++ b/changelogs/client_server/newsfragments/2343.clarification
@@ -0,0 +1 @@
+Clarify that clients should consider not requesting URL previews in encrypted rooms.