diff --git a/mods/CORE/flowlib/API.md b/mods/CORE/flowlib/API.md
index d9f54e4bd0..7ebb4cc87d 100644
--- a/mods/CORE/flowlib/API.md
+++ b/mods/CORE/flowlib/API.md
@@ -1,7 +1,11 @@
 # flowlib
 Simple flow functions.
 
-## flowlib.is_touching()
+## flowlib.is_touching(realpos, nodepos, radius)
+Return true if a sphere of <radius> at <realpos> collide with node at <nodepos>.
+* realpos: position
+* nodepos: position
+* radius: number
 
 
 ## flowlib.is_water(pos)