diff --git a/cpp/ql/src/semmle/code/cpp/security/PrintfLike.qll b/cpp/ql/src/semmle/code/cpp/security/PrintfLike.qll
index 47d0ca3aa93..b43e6cb49f1 100644
--- a/cpp/ql/src/semmle/code/cpp/security/PrintfLike.qll
+++ b/cpp/ql/src/semmle/code/cpp/security/PrintfLike.qll
@@ -1,6 +1,18 @@
+/**
+ * Provides a predicate for identifying formatting functions like `printf`.
+ * 
+ * Consider using the newer model in
+ * `semmle.code.cpp.models.interfaces.FormattingFunction` directly instead of
+ * this library.
+ */
+
 import semmle.code.cpp.commons.Printf
 import external.ExternalArtifact
 
+/**
+ * Holds if `func` is a `printf`-like formatting function and `formatArg` is
+ * the index of the format string argument.
+ */
 predicate printfLikeFunction(Function func, int formatArg) {
   formatArg = func.(FormattingFunction).getFormatParameterIndex() and
   not func instanceof UserDefinedFormattingFunction