diff --git a/docs/api/dialog.md b/docs/api/dialog.md
index 9c1f1c8addb5..14960f3f1945 100644
--- a/docs/api/dialog.md
+++ b/docs/api/dialog.md
@@ -83,3 +83,10 @@ the index of the clicked button.
 
 If a `callback` is passed, the API call would be asynchronous and the result
 would be passed via `callback(response)`
+
+## dialog.showErrorBox(title, content)
+
+Runs a modal dialog that shows an error message.
+
+This API can be called safely before the `ready` event of `app` module emits, it
+is usually used to report errors in early stage of startup.