diff --git a/bookwyrm/utils/regex.py b/bookwyrm/utils/regex.py
new file mode 100644
index 00000000..36e211d9
--- /dev/null
+++ b/bookwyrm/utils/regex.py
@@ -0,0 +1,5 @@
+''' defining regexes for regularly used concepts '''
+
+domain = r'[a-z-A-Z0-9_\-]+\.[a-z]+'
+username = r'@[a-zA-Z_\-\.0-9]+(@%s)?' % domain
+full_username = r'@[a-zA-Z_\-\.0-9]+@%s' % domain