diff --git a/esphome/core/helpers.h b/esphome/core/helpers.h
index 2e9c0e6b13..50e0a271c7 100644
--- a/esphome/core/helpers.h
+++ b/esphome/core/helpers.h
@@ -563,9 +563,11 @@ inline uint32_t fnv1_hash_object_id(const char *str, size_t len) {
 }
 
 /// snprintf-like function returning std::string of maximum length \p len (excluding null terminator).
+/// @warning Allocates heap memory. Use snprintf() with a stack buffer instead.
 std::string __attribute__((format(printf, 1, 3))) str_snprintf(const char *fmt, size_t len, ...);
 
 /// sprintf-like function returning std::string.
+/// @warning Allocates heap memory. Use snprintf() with a stack buffer instead.
 std::string __attribute__((format(printf, 1, 2))) str_sprintf(const char *fmt, ...);
 
 /// Concatenate a name with a separator and suffix using an efficient stack-based approach.