diff --git a/README.md b/README.md
index 1802e3f..55e2478 100644
--- a/README.md
+++ b/README.md
@@ -29,6 +29,8 @@ Continuous integration:
   - ![](https://github.com/siemens/CtrlppCheck/actions/workflows/main.yaml/badge.svg?branch=master) on master
   - ![](https://github.com/siemens/CtrlppCheck/actions/workflows/main.yaml/badge.svg?branch=next) on next
 
+- For the Ctrl language definition the tool depends on an installed WinCC OA version. Released major versions of WinCC OA are marked in our source code history using tags with syntax WinCC_OA_X_Y, e.g. WinCC_OA_3_19.
+
 user documentation:
 
 - [Link](docs/user.md)