diff --git a/src/app/viewer.jai b/src/app/viewer.jai
index 9698f3f..149fb70 100644
--- a/src/app/viewer.jai
+++ b/src/app/viewer.jai
@@ -544,6 +544,15 @@ viewer_ui :: () { using ImGui;
   SameLine();
   SetNextItemWidth(160);
   SliderFloat("Size", *viewer.thumb_size, 64, MCAP_PREVIEW_MAX_SIDE, "%.0f px");
+  SameLine();
+  // The OCR window (app/ocr_ui.jai): the model, GPU or CPU, and the library scan.
+  if Button("OCR")  ocr_ui.window_open = !ocr_ui.window_open;
+  if IsItemHovered() {
+    engine: *Ocr_Engine;
+    if !ocr_ui.thread_busy  engine = ocr_ui.engine;   // the background thread owns it while busy
+    if engine  SetTooltip("OCR with %, on %", engine.model.name, ifx engine.provider == .CUDA then "the GPU" else "the CPU");
+    else       SetTooltip("OCR is starting, or could not start; the OCR window says which");
+  }
 
   // A running OCR scan, as a thin bar under the search, so it shows with the OCR window closed.
   if ocr_ui.scan.running {