diff --git a/tools/idf_py_actions/mcp_ext.py b/tools/idf_py_actions/mcp_ext.py
index 5a7432bcc4d..73dcc6420ed 100644
--- a/tools/idf_py_actions/mcp_ext.py
+++ b/tools/idf_py_actions/mcp_ext.py
@@ -47,10 +47,16 @@ def _is_valid_project_dir(directory: str) -> bool:
     if not cmakelists_path.is_file():
         return False
 
+    # Normalised patterns (whitespace removed) for whitespace-insensitive matching.
+    # CMake treats whitespace inside include(...) as insignificant, so
+    # `include( $ENV{...} )` must be accepted alongside `include($ENV{...})`.
+    normalised_patterns = [''.join(p.split()) for p in CMAKE_PROJECT_LINE]
+
     try:
         with open(str(cmakelists_path), encoding='utf-8') as f:
             for line in f:
-                if any(proj_line in line for proj_line in CMAKE_PROJECT_LINE):
+                line_normalised = ''.join(line.split())
+                if any(line_normalised.startswith(pattern) for pattern in normalised_patterns):
                     return True
     except Exception:
         return False
diff --git a/tools/test_idf_py/test_mcp_ext.py b/tools/test_idf_py/test_mcp_ext.py
index d5dea6c5d56..0e5e0ac6fb9 100644
--- a/tools/test_idf_py/test_mcp_ext.py
+++ b/tools/test_idf_py/test_mcp_ext.py
@@ -189,6 +189,34 @@ class TestIsValidProjectDir:
         proj = _make_invalid_project(tmp_path / 'plain')
         assert mod._is_valid_project_dir(str(proj)) is False
 
+    def test_cmakelists_with_spaces_in_include(
+        self, tmp_path: Path, mcp_ext: tuple[types.ModuleType, _MockFastMCP]
+    ) -> None:
+        mod, _ = mcp_ext
+        path = tmp_path / 'spaced'
+        path.mkdir()
+        (path / 'CMakeLists.txt').write_text(
+            'cmake_minimum_required(VERSION 3.16)\n'
+            'include( $ENV{IDF_PATH}/tools/cmake/project.cmake )\n'
+            'project(hello_world)\n',
+            encoding='utf-8',
+        )
+        assert mod._is_valid_project_dir(str(path)) is True
+
+    def test_commented_out_include_is_rejected(
+        self, tmp_path: Path, mcp_ext: tuple[types.ModuleType, _MockFastMCP]
+    ) -> None:
+        mod, _ = mcp_ext
+        path = tmp_path / 'commented'
+        path.mkdir()
+        (path / 'CMakeLists.txt').write_text(
+            'cmake_minimum_required(VERSION 3.16)\n'
+            '# include($ENV{IDF_PATH}/tools/cmake/project.cmake)\n'
+            'project(hello_world)\n',
+            encoding='utf-8',
+        )
+        assert mod._is_valid_project_dir(str(path)) is False
+
     def test_empty_string(self, mcp_ext: tuple[types.ModuleType, _MockFastMCP]) -> None:
         mod, _ = mcp_ext
         assert mod._is_valid_project_dir('') is False