diff --git a/filter.go b/filter.go
index e4e7628..2a0c37f 100644
--- a/filter.go
+++ b/filter.go
@@ -14,6 +14,8 @@
 
 package gomatrix
 
+import "errors"
+
 //Filter is used by clients to specify how the server should filter responses to e.g. sync requests
 //Specified by: https://matrix.org/docs/spec/client_server/r0.2.0.html#filtering
 type Filter struct {
@@ -21,23 +23,68 @@ type Filter struct {
 	EventFields []string   `json:"event_fields,omitempty"`
 	EventFormat string     `json:"event_format,omitempty"`
 	Presence    FilterPart `json:"presence,omitempty"`
-	Room        struct {
-		AccountData  FilterPart `json:"account_data,omitempty"`
-		Ephemeral    FilterPart `json:"ephemeral,omitempty"`
-		IncludeLeave bool       `json:"include_leave,omitempty"`
-		NotRooms     []string   `json:"not_rooms,omitempty"`
-		Rooms        []string   `json:"rooms,omitempty"`
-		State        FilterPart `json:"state,omitempty"`
-		Timeline     FilterPart `json:"timeline,omitempty"`
-	} `json:"room,omitempty"`
+	Room        RoomFilter `json:"room,omitempty"`
 }
 
-type FilterPart struct {
-	NotRooms   []string `json:"not_rooms,omitempty"`
-	Rooms      []string `json:"rooms,omitempty"`
-	Limit      *int     `json:"limit,omitempty"`
-	NotSenders []string `json:"not_senders,omitempty"`
-	NotTypes   []string `json:"not_types,omitempty"`
-	Senders    []string `json:"senders,omitempty"`
-	Types      []string `json:"types,omitempty"`
+// RoomFilter is used to define filtering rules for room events
+type RoomFilter struct {
+	AccountData  FilterPart `json:"account_data,omitempty"`
+	Ephemeral    FilterPart `json:"ephemeral,omitempty"`
+	IncludeLeave bool       `json:"include_leave,omitempty"`
+	NotRooms     []string   `json:"not_rooms,omitempty"`
+	Rooms        []string   `json:"rooms,omitempty"`
+	State        FilterPart `json:"state,omitempty"`
+	Timeline     FilterPart `json:"timeline,omitempty"`
+}
+
+// FilterPart is used to define filtering rules for specific categories of events
+type FilterPart struct {
+	NotRooms    []string `json:"not_rooms,omitempty"`
+	Rooms       []string `json:"rooms,omitempty"`
+	Limit       int      `json:"limit,omitempty"`
+	NotSenders  []string `json:"not_senders,omitempty"`
+	NotTypes    []string `json:"not_types,omitempty"`
+	Senders     []string `json:"senders,omitempty"`
+	Types       []string `json:"types,omitempty"`
+	ContainsURL *bool    `json:"contains_url,omitempty"`
+}
+
+// Validate checks if the filter contains valid property values
+func (filter *Filter) Validate() error {
+	if filter.EventFormat != "client" && filter.EventFormat != "federation" {
+		return errors.New("Bad event_format value. Must be one of [\"client\", \"federation\"]")
+	}
+	return nil
+}
+
+// DefaultFilter returns the default filter used by the Matrix server if no filter is provided in the request
+func DefaultFilter() Filter {
+	return Filter{
+		AccountData: DefaultFilterPart(),
+		EventFields: nil,
+		EventFormat: "client",
+		Presence:    DefaultFilterPart(),
+		Room: RoomFilter{
+			AccountData:  DefaultFilterPart(),
+			Ephemeral:    DefaultFilterPart(),
+			IncludeLeave: false,
+			NotRooms:     nil,
+			Rooms:        nil,
+			State:        DefaultFilterPart(),
+			Timeline:     DefaultFilterPart(),
+		},
+	}
+}
+
+// DefaultFilterPart returns the default filter part used by the Matrix server if no filter is provided in the request
+func DefaultFilterPart() FilterPart {
+	return FilterPart{
+		NotRooms:   nil,
+		Rooms:      nil,
+		Limit:      20,
+		NotSenders: nil,
+		NotTypes:   nil,
+		Senders:    nil,
+		Types:      nil,
+	}
 }