diff --git a/src/atm/main.py b/src/atm/main.py
index d74d611..321cdea 100644
--- a/src/atm/main.py
+++ b/src/atm/main.py
@@ -62,6 +62,9 @@ def main(argv=None) -> None:
         metavar="PATH", help="Journal JSONL file (default: trades.jsonl)",
     )
 
+    # debug
+    sub.add_parser("debug", help="Capture one frame, run detector, annotate + print result")
+
     # report
     p_report = sub.add_parser("report", help="Print weekly performance report")
     p_report.add_argument(
@@ -80,6 +83,7 @@ def main(argv=None) -> None:
         "label": _cmd_label,
         "dryrun": _cmd_dryrun,
         "run": _cmd_run,
+        "debug": _cmd_debug,
         "journal": _cmd_journal,
         "report": _cmd_report,
     }
@@ -140,6 +144,72 @@ def _cmd_journal(args) -> None:
     j.add(entry)
 
 
+def _cmd_debug(args) -> None:
+    """One-shot capture + detect. Saves annotated PNG. Prints classification."""
+    from datetime import datetime
+    try:
+        from atm.detector import Detector
+        from atm.vision import crop_roi
+    except ImportError as exc:
+        sys.exit(f"debug module deps missing: {exc}")
+
+    cfg = Config.load_current(Path("configs"))
+    capture = _build_capture(cfg)
+    frame = capture()
+    if frame is None:
+        sys.exit("capture returned None (window not found or region invalid)")
+
+    out_dir = Path("logs")
+    out_dir.mkdir(exist_ok=True)
+    ts = datetime.now().strftime("%Y%m%d_%H%M%S")
+
+    import cv2  # type: ignore[import-untyped]
+    full_path = out_dir / f"debug_full_{ts}.png"
+    cv2.imwrite(str(full_path), frame)
+    print(f"captured frame: {frame.shape} → {full_path}")
+
+    # crop dot_roi + run detector
+    try:
+        dot_crop = crop_roi(frame, cfg.dot_roi)
+        dot_path = out_dir / f"debug_dot_roi_{ts}.png"
+        cv2.imwrite(str(dot_path), dot_crop)
+        print(f"dot_roi crop: {dot_crop.shape} → {dot_path}")
+    except Exception as exc:
+        sys.exit(f"dot_roi crop failed: {exc}")
+
+    det = Detector(cfg, capture)
+    res = det.step(0.0)
+    print("---")
+    print(f"window_found: {res.window_found}")
+    print(f"dot_found:    {res.dot_found}")
+    if res.match is not None:
+        print(f"rgb:          {res.rgb}")
+        print(f"classified:   {res.match.name}  distance={res.match.distance:.1f}  confidence={res.match.confidence:.2f}")
+    else:
+        print("no match (dot not found or UNKNOWN classification)")
+    print(f"accepted:     {res.accepted}  color={res.color}")
+
+    # Annotate: draw dot_roi rect + mark detected dot
+    annotated = frame.copy()
+    x, y, w, h = cfg.dot_roi.x, cfg.dot_roi.y, cfg.dot_roi.w, cfg.dot_roi.h
+    cv2.rectangle(annotated, (x, y), (x + w, y + h), (0, 255, 255), 2)
+    if res.dot_found and res.match is not None:
+        # re-find dot to know exact x,y for annotation
+        from atm.vision import find_rightmost_dot
+        bg_rgb = (18, 18, 18)
+        if "background" in cfg.colors:
+            bg_rgb = cfg.colors["background"].rgb
+        dot_crop = crop_roi(frame, cfg.dot_roi)
+        pos = find_rightmost_dot(dot_crop, bg_rgb)
+        if pos is not None:
+            dx, dy = pos
+            cx, cy = x + dx, y + dy
+            cv2.circle(annotated, (cx, cy), 12, (0, 0, 255), 3)
+    annotated_path = out_dir / f"debug_annotated_{ts}.png"
+    cv2.imwrite(str(annotated_path), annotated)
+    print(f"annotated:    {annotated_path}")
+
+
 def _cmd_report(args) -> None:
     try:
         from atm.journal import Journal