# Format suffixes > Section 6.2.1 does not say that content negotiation should be used all the time. > > — Roy Fielding, [REST discuss mailing list][cite] A common pattern for Web APIs is to use filename extensions on URLs to provide an endpoint for a given media type. For example, 'http://example.com/api/users.json' to serve a JSON representation. Adding format-suffix patterns to each individual entry in the URLconf for your API is error-prone and non-DRY, so REST framework provides a shortcut to adding these patterns to your URLConf. ## format_suffix_patterns **Signature**: format_suffix_patterns(urlpatterns, suffix_required=False, allowed=None) Returns a URL pattern list which includes format suffix patterns appended to each of the URL patterns provided. Arguments: * **urlpatterns**: Required. A URL pattern list. * **suffix_required**: Optional. A boolean indicating if suffixes in the URLs should be optional or mandatory. Defaults to `False`, meaning that suffixes are optional by default. * **allowed**: Optional. A list or tuple of valid format suffixes. If not provided, a wildcard format suffix pattern will be used. Example: from rest_framework.urlpatterns import format_suffix_patterns from blog import views urlpatterns = [ url(r'^/$', views.apt_root), url(r'^comments/$', views.comment_list), url(r'^comments/(?P[0-9]+)/$', views.comment_detail) ] urlpatterns = format_suffix_patterns(urlpatterns, allowed=['json', 'html']) When using `format_suffix_patterns`, you must make sure to add the `'format'` keyword argument to the corresponding views. For example: @api_view(('GET', 'POST')) def comment_list(request, format=None): # do stuff... Or with class based views: class CommentList(APIView): def get(self, request, format=None): # do stuff... def post(self, request, format=None): # do stuff... The name of the kwarg used may be modified by using the `FORMAT_SUFFIX_KWARG` setting. Also note that `format_suffix_patterns` does not support descending into `include` URL patterns. --- ## Accept headers vs. format suffixes There seems to be a view among some of the Web community that filename extensions are not a RESTful pattern, and that `HTTP Accept` headers should always be used instead. It is actually a misconception. For example, take the following quote from Roy Fielding discussing the relative merits of query parameter media-type indicators vs. file extension media-type indicators: “That's why I always prefer extensions. Neither choice has anything to do with REST.” — Roy Fielding, [REST discuss mailing list][cite2] The quote does not mention Accept headers, but it does make it clear that format suffixes should be considered an acceptable pattern. [cite]: http://tech.groups.yahoo.com/group/rest-discuss/message/5857 [cite2]: http://tech.groups.yahoo.com/group/rest-discuss/message/14844