diff --git a/.flake8 b/.flake8
new file mode 100644
index 0000000..3115e97
--- /dev/null
+++ b/.flake8
@@ -0,0 +1,3 @@
+[flake8]
+max-line-length = 80
+extend-ignore = E203, E302
\ No newline at end of file
diff --git a/pyModeS/extra/demod2400/core.pyi b/pyModeS/extra/demod2400/core.pyi
new file mode 100644
index 0000000..a3c3ee7
--- /dev/null
+++ b/pyModeS/extra/demod2400/core.pyi
@@ -0,0 +1,4 @@
+import numpy as np
+import numpy.typing as npt
+
+def demod2400(data: npt.NDArray[np.uint16], timestamp: float): ...