diff --git a/content/docs/app-server.md b/content/docs/app-server.md
index f4ad8a1..00664cb 100644
--- a/content/docs/app-server.md
+++ b/content/docs/app-server.md
@@ -117,6 +117,7 @@ GET parameters can be used to filter and paginate the returned posts.
 | `before_id_entity` | The entity which made the post that has the id given in `before_id`.  This can be omitted if the post's owner is the one receiving the `GET /posts` request.  |
 | `since_time` | Posts with `received_at` greater than the specified unix epoch. |
 | `before_time` | Posts with `received_at` less than the specified unix epoch. |
+| `sort_by` | Possible values are `received_at` (default) and `published_at`. This effects `since_time` and `before_time`. |
 | `entity` | Posts published by the specified entity. |
 | `mentioned_entity` | Posts that mention the specified entity. |
 | `post_types` | Posts that match specific comma-separated type URIs. |