diff --git a/CLAUDE.md b/CLAUDE.md
index 71cace5..476dbd9 100644
--- a/CLAUDE.md
+++ b/CLAUDE.md
@@ -87,3 +87,11 @@ Each server is a systemd unit `mcp-<name>.service` (uvicorn). Each subdomain is
 - Reference other tools ("Use read_attachment with the index from read_mail")
 - Return structured text, not JSON
 - Include IDs/keys in output so Claude can chain to detail tools
+
+## Test-/Dev-User mcptest
+
+Die Test-Suite laeuft auf einem isolierten `mcptest`-User (NICHT Stefans Daten):
+`USER_ALIASES = {"test": "mcptest"}`. Eigene Backends: Radicale-User mcptest, oCIS-User
+mcptest, lokales Joplin-Profil (:41186, `joplin-cli-mcptest.service`), Test-Maildir
+`tests/testdata/maildir/`. Dient auch als Dev-Sandbox. Vollstaendige Doku + Provisioning:
+`tests/MCPTEST.md`. Creds: `/root/.mcptest-creds` (600) + `config.json`.