diff --git a/README.md b/README.md
index 40f9ffc..d83efa5 100644
--- a/README.md
+++ b/README.md
@@ -1,5 +1,7 @@
 # external-signer-pkcs11
 
+> Specification: https://openwebstandard.org/rfc1
+
 
 Cross compile:
 ```shell