diff --git a/src/vitis_checker.py b/src/vitis_checker.py
index 0b0f65f..efd4310 100644
--- a/src/vitis_checker.py
+++ b/src/vitis_checker.py
@@ -60,7 +60,8 @@ TOOL_ALIASES: dict[str, list[str]] = {
 }
 
 # Product subdirectories under xilinx_root to scan (in preference order)
-_PRODUCT_DIRS = ("Vitis", "Vivado")
+# SDK covers pre-2019 installations where xsct lived in SDK/*/bin/
+_PRODUCT_DIRS = ("Vitis", "Vivado", "SDK")
 
 
 # ── Version helpers ──────────────────────────────────────────────────
@@ -163,9 +164,9 @@ def _find_executable(
     """Find an executable by name using PATH, Vitis, and Xilinx root.
 
     Search order:
-    1. System PATH (shutil.which)
+    1. System PATH (shutil.which) — tries bare name, .exe, .bat on Windows
     2. vitis_path/bin (legacy config)
-    3. xilinx_root/Vitis/*/bin and Vivado/*/bin — pick NEWEST version
+    3. xilinx_root/Vitis/*/bin, Vivado/*/bin, SDK/*/bin — pick NEWEST version
     4. Common install paths (cross-platform)
 
     Args:
@@ -179,16 +180,22 @@ def _find_executable(
     """
     exec_suffix = ".exe" if system == "windows" else ""
 
-    # 1. System PATH
-    found = shutil.which(f"{exec_name}{exec_suffix}")
+    # 1. System PATH — search without explicit extension first
+    #    so Windows PATHEXT resolves .bat/.exe/.cmd automatically
+    found = shutil.which(exec_name)
+    if not found and exec_suffix:
+        found = shutil.which(f"{exec_name}{exec_suffix}")
+        if not found:
+            found = shutil.which(f"{exec_name}.bat")
     if found:
         return found
 
     # 2. Legacy vitis_path/bin
     if vitis_path:
-        candidate = Path(vitis_path) / "bin" / f"{exec_name}{exec_suffix}"
-        if candidate.is_file():
-            return str(candidate)
+        for sfx in (".bat", ".exe") if system == "windows" else (exec_suffix,):
+            candidate = Path(vitis_path) / "bin" / f"{exec_name}{sfx}"
+            if candidate.is_file():
+                return str(candidate)
 
     # 3. Scan xilinx_root — pick newest version across Vitis + Vivado
     if xilinx_root:
@@ -203,8 +210,8 @@ def _find_executable(
     if system == "windows":
         common: list[str] = []
         for sfx in (".bat", ".exe"):
-            for ver in ("2023.2", "2022.2"):
-                for prod in ("Vitis", "Vivado"):
+            for ver in ("2023.2", "2022.2", "2018.3"):
+                for prod in ("Vitis", "Vivado", "SDK"):
                     common.append(f"C:/Xilinx/{prod}/{ver}/bin/{exec_name}{sfx}")
     else:
         common = [