diff --git a/config/chromium-flags.conf b/config/chromium-flags.conf
index 5edf16a7..1fe08716 100644
--- a/config/chromium-flags.conf
+++ b/config/chromium-flags.conf
@@ -2,4 +2,4 @@
 --ozone-platform-hint=wayland
 --password-store=gnome-libsecret
 --enable-features=TouchpadOverscrollHistoryNavigation
---load-extension=/usr/share/omarchy/default/chromium/extensions/copy-url,/usr/share/omarchy/default/chromium/extensions/yt-dlp
+--load-extension=/usr/share/omarchy/default/chromium/extensions/copy-url,/usr/share/omarchy/default/chromium/extensions/yt-dlp,/usr/share/omarchy/default/chromium/extensions/whatsapp-slim
diff --git a/default/chromium/extensions/whatsapp-slim/manifest.json b/default/chromium/extensions/whatsapp-slim/manifest.json
new file mode 100644
index 00000000..48471bd5
--- /dev/null
+++ b/default/chromium/extensions/whatsapp-slim/manifest.json
@@ -0,0 +1,12 @@
+{
+  "manifest_version": 3,
+  "name": "WhatsApp Slim",
+  "version": "1.0",
+  "description": "Collapse WhatsApp Web's chat list to an avatar rail in narrow windows, this extension is installed by Omarchy",
+  "content_scripts": [
+    {
+      "matches": ["https://web.whatsapp.com/*"],
+      "css": ["whatsapp.css"]
+    }
+  ]
+}
diff --git a/default/chromium/extensions/whatsapp-slim/whatsapp.css b/default/chromium/extensions/whatsapp-slim/whatsapp.css
new file mode 100644
index 00000000..db6684e3
--- /dev/null
+++ b/default/chromium/extensions/whatsapp-slim/whatsapp.css
@@ -0,0 +1,64 @@
+/* Collapse WhatsApp Web's chat list to a Signal-style avatar rail when the
+ * window is too narrow to show both the full list and the conversation.
+ * Leans on WhatsApp's stable structural ids (#side, #main, #pane-side) and
+ * data-testid hooks rather than its obfuscated, frequently-churning class
+ * names. */
+
+@media (max-width: 1100px) {
+  /* The chat-list column (title header + #side) becomes an avatar rail */
+  div:has(> div#side) {
+    flex: 0 0 90px !important;
+    min-width: 90px !important;
+    max-width: 90px !important;
+  }
+
+  /* Chat-list title bar, search, filter chips, and banner don't fit.
+   * Scoped to the column wrapper: the left icon nav rail confusingly
+   * shares the same chatlist-header testid and must survive. */
+  div:has(> div#side) > header,
+  #side > div:first-child,
+  #side [role="tablist"],
+  #side span[data-testid="chat-butterbar"] {
+    display: none !important;
+  }
+
+  /* The rail doesn't need a visible scrollbar, and horizontal overflow
+   * from the collapsed rows must not wiggle */
+  #pane-side {
+    overflow-x: hidden !important;
+    scrollbar-width: none !important;
+  }
+
+  /* Chat rows: keep the avatar column, collapse the text/preview columns
+   * without display:none so the unread badge can be resurrected */
+  [data-testid="cell-frame-container"] {
+    position: relative !important;
+  }
+
+  [data-testid="cell-frame-container"] > div:not(:first-child) {
+    visibility: hidden !important;
+    width: 0 !important;
+    min-width: 0 !important;
+    overflow: hidden !important;
+  }
+
+  /* Float the unread badge over the avatar's top-right corner */
+  [data-testid="cell-frame-container"] span[aria-label*="unread"] {
+    visibility: visible !important;
+    position: absolute !important;
+    top: 2px !important;
+    left: 50px !important;
+  }
+
+  /* The empty drawer overlay keeps the stock chat-list width, which
+   * strands its divider border in the middle of the conversation */
+  [data-testid="drawer-middle"] {
+    border-left: none !important;
+  }
+
+  /* Let the app shrink below WhatsApp's default minimum width */
+  #app,
+  #app .two {
+    min-width: 0 !important;
+  }
+}
diff --git a/migrations/1785543725.sh b/migrations/1785543725.sh
new file mode 100644
index 00000000..71e1abea
--- /dev/null
+++ b/migrations/1785543725.sh
@@ -0,0 +1,20 @@
+echo "Add WhatsApp Slim extension to Chromium-based browsers"
+
+WHATSAPP_SLIM_EXT="$OMARCHY_PATH/default/chromium/extensions/whatsapp-slim"
+
+add_whatsapp_slim_extension() {
+  local file=$1
+
+  [[ -f $file ]] || return 0
+  grep -q "extensions/whatsapp-slim" "$file" && return 0
+
+  if grep -q "^--load-extension=" "$file"; then
+    sed -i --follow-symlinks "s|^--load-extension=\(.*\)$|--load-extension=\1,$WHATSAPP_SLIM_EXT|" "$file"
+  else
+    echo "--load-extension=$WHATSAPP_SLIM_EXT" >>"$file"
+  fi
+}
+
+for conf in chromium chrome google-chrome brave brave-beta brave-nightly brave-origin-beta microsoft-edge-stable; do
+  add_whatsapp_slim_extension "$HOME/.config/$conf-flags.conf"
+done