diff --git a/docs/en/api-guides/build-system.rst b/docs/en/api-guides/build-system.rst
index b16bd4e95d..a344746e66 100644
--- a/docs/en/api-guides/build-system.rst
+++ b/docs/en/api-guides/build-system.rst
@@ -114,6 +114,7 @@ Here is a list of some useful options:
 
 Note that some older versions of CCache may exhibit bugs on some platforms, so if files are not rebuilt as expected then try disabling ccache and build again. CCache can be enabled by default by setting the ``IDF_ENABLE_CCACHE`` environment variable to a non-zero value.
 - ``-v`` flag causes both ``idf.py`` and the build system to produce verbose build output. This can be useful for debugging build problems.
+- ``--cmake-warn-uninitialized`` (or ``-w``) will cause CMake to print uninitialized variable warnings inside the project directory (not for directories not found inside the project directory). This only controls CMake variable warnings inside CMake itself, not other types of build warnings. This option can also be set permanently by setting the ``IDF_CMAKE_WARN_UNINITIALIZED`` environment variable to a non-zero value.
 
 Using CMake Directly
 --------------------
diff --git a/tools/idf_py_actions/core_ext.py b/tools/idf_py_actions/core_ext.py
index 5c64e257aa..cb4c333bc1 100644
--- a/tools/idf_py_actions/core_ext.py
+++ b/tools/idf_py_actions/core_ext.py
@@ -217,8 +217,10 @@ def action_extensions(base_actions, project_path):
                 "default": None,
             },
             {
-                "names": ["-n", "--no-warnings"],
-                "help": "Disable Cmake warnings.",
+                "names": ["-w/-n", "--cmake-warn-uninitialized/--no-warnings"],
+                "help": ("Enable CMake uninitialized variable warnings for CMake files inside the project directory. "
+                         "(--no-warnings is now the default, and doesn't need to be specified.)"),
+                "envvar": "IDF_CMAKE_WARN_UNINITIALIZED",
                 "is_flag": True,
                 "default": False,
             },
diff --git a/tools/idf_py_actions/tools.py b/tools/idf_py_actions/tools.py
index c1d1d907fd..80ee86b621 100644
--- a/tools/idf_py_actions/tools.py
+++ b/tools/idf_py_actions/tools.py
@@ -178,7 +178,7 @@ def ensure_build_directory(args, prog_name, always_run_cmake=False):
                 "-DPYTHON_DEPS_CHECKED=1",
                 "-DESP_PLATFORM=1",
             ]
-            if not args.no_warnings:
+            if args.cmake_warn_uninitialized:
                 cmake_args += ["--warn-uninitialized"]
 
             if args.define_cache_entry: