diff --git a/.jules/bolt.md b/.jules/bolt.md
new file mode 100644
index 0000000..1ac5432
--- /dev/null
+++ b/.jules/bolt.md
@@ -0,0 +1,3 @@
+## 2026-01-31 - XSync vs XFlush in X11 Animations
+**Learning:** `XSync(dpy, False)` is a blocking round-trip to the X server, while `XFlush(dpy)` sends requests asynchronously. In tight loops like animations (`animateclient` in `animation.c`) or interactive resizing (`resizeclient` in `client.c`), `XSync` can significantly degrade frame rates by forcing the client to wait for the server on every frame.
+**Action:** Replace `XSync` with `XFlush` in performance-critical rendering/update paths where strict synchronization is not required for correctness. Ensure to verify that side effects (like event generation) are not implicitly relied upon by subsequent synchronous checks.
diff --git a/client.c b/client.c
index 13f1e27..7bb19b3 100644
--- a/client.c
+++ b/client.c
@@ -279,7 +279,10 @@ void resizeclient(Client *c, int x, int y, int w, int h) {
     XConfigureWindow(dpy, c->win,
                      CWX | CWY | CWWidth | CWHeight | CWBorderWidth, &wc);
     configure(c);
-    XSync(dpy, False);
+    /* Optimization: Use XFlush instead of XSync to avoid blocking round-trip to X server.
+     * This significantly improves performance during animations and mouse resizing.
+     */
+    XFlush(dpy);
 }
 
 void updatetitle(Client *c) {
diff --git a/drw.c b/drw.c
index 7e99a38..ed067de 100644
--- a/drw.c
+++ b/drw.c
@@ -494,7 +494,10 @@ void drw_map(Drw *drw, Window win, int x, int y, unsigned int w,
     }
 
     XCopyArea(drw->dpy, drw->drawable, win, drw->gc, x, y, w, h, x, y);
-    XSync(drw->dpy, False);
+    /* Optimization: Use XFlush instead of XSync to avoid blocking round-trip.
+     * XCopyArea is efficient, and we just need to ensure the request is sent.
+     */
+    XFlush(drw->dpy);
 }
 
 unsigned int drw_fontset_getwidth(Drw *drw, const char *text) {