diff --git a/app/docs/interact/web-ui/page.mdx b/app/docs/interact/web-ui/page.mdx
index af7feeb..70772eb 100644
--- a/app/docs/interact/web-ui/page.mdx
+++ b/app/docs/interact/web-ui/page.mdx
@@ -72,6 +72,11 @@ project folder's `⋯` menu and choose `Project settings`, then set any of:
 - **Default agent** for the session.
 - **Random worktree**, which branches each new session into its own fresh git
   worktree.
+- **Base branch** the worktree forks from. This field appears only when
+  **Random worktree** is on (it's the branch the fresh worktree is cut from).
+  Leave it blank to fall through to your user-global **Default base branch**
+  (**Settings › Git**); a value set here takes precedence over that global
+  default.
 
 New sessions started in that project pre-fill the composer from these defaults.
 Nothing is locked in: every field is still editable before you send, any default
@@ -90,6 +95,11 @@ To avoid retyping the same base, set a **Default base branch** under
 **Settings › Git**. The composer then auto-fills that value whenever you name a
 new worktree branch; leave the setting blank to turn auto-fill off.
 
+A project can override this per-project: the **Base branch** in
+[Project settings](#project-settings-and-defaults) wins over the global default,
+so the composer auto-fills the project's base branch when set and falls back to
+the global default (then to blank) when it isn't.
+
 ![Setting a default base branch for worktrees](/images/docs/git_worktree_setting.gif)
 
 ### Choose the launch model