diff --git a/app/__init__.py b/app/__init__.py
index d3732e208..e3ec26fce 100644
--- a/app/__init__.py
+++ b/app/__init__.py
@@ -83,6 +83,10 @@ from app.notify_client.template_statistics_api_client import (
     template_statistics_client,
 )
 from app.notify_client.user_api_client import user_api_client
+from app.url_converters import (
+    LetterFileExtensionConverter,
+    TemplateTypeConverter,
+)
 from app.utils import format_thousands, get_logo_cdn_domain, id_safe
 
 login_manager = LoginManager()
@@ -229,6 +233,8 @@ def init_app(application):
         }
 
     application.url_map.converters['uuid'].to_python = lambda self, value: value
+    application.url_map.converters['template_type'] = TemplateTypeConverter
+    application.url_map.converters['letter_file_extension'] = LetterFileExtensionConverter
 
 
 def convert_to_boolean(value):
diff --git a/app/main/views/jobs.py b/app/main/views/jobs.py
index 06f225e90..390eb7325 100644
--- a/app/main/views/jobs.py
+++ b/app/main/views/jobs.py
@@ -213,7 +213,7 @@ def view_job_updates(service_id, job_id):
 
 
 @main.route('/services/<uuid:service_id>/notifications', methods=['GET', 'POST'])
-@main.route('/services/<uuid:service_id>/notifications/<message_type>', methods=['GET', 'POST'])
+@main.route('/services/<uuid:service_id>/notifications/<template_type:message_type>', methods=['GET', 'POST'])
 @user_has_permissions()
 def view_notifications(service_id, message_type=None):
     return render_template(
@@ -237,7 +237,7 @@ def view_notifications(service_id, message_type=None):
 
 
 @main.route('/services/<uuid:service_id>/notifications.json', methods=['GET', 'POST'])
-@main.route('/services/<uuid:service_id>/notifications/<message_type>.json', methods=['GET', 'POST'])
+@main.route('/services/<uuid:service_id>/notifications/<template_type:message_type>.json', methods=['GET', 'POST'])
 @user_has_permissions()
 def get_notifications_as_json(service_id, message_type=None):
     return jsonify(get_notifications(
@@ -245,15 +245,14 @@ def get_notifications_as_json(service_id, message_type=None):
     ))
 
 
-@main.route('/services/<uuid:service_id>/notifications/<message_type>.csv', endpoint="view_notifications_csv")
+@main.route('/services/<uuid:service_id>/notifications.csv', endpoint="view_notifications_csv")
+@main.route('/services/<uuid:service_id>/notifications/<template_type:message_type>.csv', endpoint="view_notifications_csv")
 @user_has_permissions()
 def get_notifications(service_id, message_type, status_override=None):
     # TODO get the api to return count of pages as well.
     page = get_page_from_request()
     if page is None:
         abort(404, "Invalid page argument ({}).".format(request.args.get('page')))
-    if message_type not in ['email', 'sms', 'letter', None]:
-        abort(404)
     filter_args = parse_filter_args(request.args)
     filter_args['status'] = set_status_filters(filter_args)
     service_data_retention_days = None
diff --git a/app/main/views/notifications.py b/app/main/views/notifications.py
index f02db4dfd..5cff773e7 100644
--- a/app/main/views/notifications.py
+++ b/app/main/views/notifications.py
@@ -8,7 +8,6 @@ from datetime import datetime
 from dateutil import parser
 from flask import (
     Response,
-    abort,
     flash,
     jsonify,
     redirect,
@@ -180,15 +179,11 @@ def get_preview_error_image():
         return file.read()
 
 
-@main.route("/services/<uuid:service_id>/notification/<uuid:notification_id>.<filetype>")
+@main.route("/services/<uuid:service_id>/notification/<uuid:notification_id>.<letter_file_extension:filetype>")
 @user_has_permissions('view_activity')
 def view_letter_notification_as_preview(
     service_id, notification_id, filetype, with_metadata=False
 ):
-
-    if filetype not in ('pdf', 'png'):
-        abort(404)
-
     try:
         preview = notification_api_client.get_notification_letter_preview(
             service_id,
diff --git a/app/main/views/templates.py b/app/main/views/templates.py
index 49ca6cfd2..e42aba388 100644
--- a/app/main/views/templates.py
+++ b/app/main/views/templates.py
@@ -106,8 +106,8 @@ def start_tour(service_id, template_id):
 
 @main.route("/services/<uuid:service_id>/templates", methods=['GET', 'POST'])
 @main.route("/services/<uuid:service_id>/templates/folders/<uuid:template_folder_id>", methods=['GET', 'POST'])
-@main.route("/services/<uuid:service_id>/templates/<template_type>", methods=['GET', 'POST'])
-@main.route("/services/<uuid:service_id>/templates/<template_type>/folders/<uuid:template_folder_id>", methods=['GET', 'POST'])
+@main.route("/services/<uuid:service_id>/templates/<template_type:template_type>", methods=['GET', 'POST'])
+@main.route("/services/<uuid:service_id>/templates/<template_type:template_type>/folders/<uuid:template_folder_id>", methods=['GET', 'POST'])
 @user_has_permissions()
 def choose_template(service_id, template_type='all', template_folder_id=None):
     template_folder = current_service.get_template_folder(template_folder_id)
@@ -406,11 +406,11 @@ def _get_template_copy_name(template, existing_templates):
 
 @main.route((
     '/services/<uuid:service_id>/templates/action-blocked/'
-    '<notification_type>'
+    '<template_type:notification_type>'
 ))
 @main.route((
     '/services/<uuid:service_id>/templates/action-blocked/'
-    '<notification_type>/<return_to>/<uuid:template_id>'
+    '<template_type:notification_type>/<return_to>/<uuid:template_id>'
 ))
 @user_has_permissions('manage_templates')
 def action_blocked(service_id, notification_type, return_to='add_new_template', template_id=None):
@@ -505,18 +505,16 @@ def delete_template_folder(service_id, template_folder_id):
 
 
 @main.route(
-    "/services/<uuid:service_id>/templates/add-<template_type>",
+    "/services/<uuid:service_id>/templates/add-<template_type:template_type>",
     methods=['GET', 'POST'],
 )
 @main.route(
-    "/services/<uuid:service_id>/templates/folders/<uuid:template_folder_id>/add-<template_type>",
+    "/services/<uuid:service_id>/templates/folders/<uuid:template_folder_id>/add-<template_type:template_type>",
     methods=['GET', 'POST'],
 )
 @user_has_permissions('manage_templates')
 def add_service_template(service_id, template_type, template_folder_id=None):
 
-    if template_type not in ['sms', 'email', 'letter']:
-        abort(404)
     if not current_service.has_permission('letter') and template_type == 'letter':
         abort(403)
 
diff --git a/app/url_converters.py b/app/url_converters.py
new file mode 100644
index 000000000..e90012f59
--- /dev/null
+++ b/app/url_converters.py
@@ -0,0 +1,11 @@
+from werkzeug.routing import BaseConverter
+
+
+class TemplateTypeConverter(BaseConverter):
+
+    regex = '(?:email|sms|letter)'
+
+
+class LetterFileExtensionConverter(BaseConverter):
+
+    regex = '(?:pdf|png)'