diff --git a/init.lua b/init.lua
index 4a8a4ae..9121cd6 100644
--- a/init.lua
+++ b/init.lua
@@ -2,4 +2,20 @@
 -- See: meta/docs/superpowers/specs/2026-05-16-api-doc-convention-design.md
 local M = {}
 
+-- Extracts public/private surface from Lua source code.
+-- Convention: `M.<name> = function(...)` is public; `M._<name> = ...` is private.
+-- Returns: { public = ["foo","bar",...], private = ["_baz",...] }
+function M.parse_lua_surface(source_string)
+    local public  = {}
+    local private = {}
+    for name in string.gmatch(source_string, "M%.([_%w]+)%s*=%s*function") do
+        if string.sub(name, 1, 1) == "_" then
+            table.insert(private, name)
+        else
+            table.insert(public, name)
+        end
+    end
+    return { public = public, private = private }
+end
+
 return M