diff --git a/eclair-core/src/main/scala/fr/acinq/eclair/wire/protocol/OfferTypes.scala b/eclair-core/src/main/scala/fr/acinq/eclair/wire/protocol/OfferTypes.scala
index 859a2b6dc0..5ad99acf88 100644
--- a/eclair-core/src/main/scala/fr/acinq/eclair/wire/protocol/OfferTypes.scala
+++ b/eclair-core/src/main/scala/fr/acinq/eclair/wire/protocol/OfferTypes.scala
@@ -314,6 +314,10 @@ object OfferTypes {
       Right(Offer(records))
     }
 
+    /**
+     * An offer string can be split with '+' to fit in places with a low character limit. This validates that the string adheres to the spec format to guard against copy-pasting errors.
+     * @return a lowercase string with '+' and whitespaces removed
+     */
     def validateFormat(s: String): String = {
       val lowercase = s.toLowerCase
       require(s == lowercase || s == s.toUpperCase)