diff --git a/nip11/nip11_test.go b/nip11/nip11_test.go
new file mode 100644
index 0000000..a1a0a89
--- /dev/null
+++ b/nip11/nip11_test.go
@@ -0,0 +1,30 @@
+package nip11
+
+import "testing"
+
+func TestAddSupportedNIP(t *testing.T) {
+	info := RelayInformationDocument{}
+	info.AddSupportedNIP(12)
+	info.AddSupportedNIP(12)
+	info.AddSupportedNIP(13)
+	info.AddSupportedNIP(1)
+	info.AddSupportedNIP(12)
+	info.AddSupportedNIP(44)
+	info.AddSupportedNIP(2)
+	info.AddSupportedNIP(13)
+	info.AddSupportedNIP(2)
+	info.AddSupportedNIP(13)
+	info.AddSupportedNIP(0)
+	info.AddSupportedNIP(17)
+	info.AddSupportedNIP(19)
+	info.AddSupportedNIP(1)
+	info.AddSupportedNIP(18)
+
+	for i, v := range []int{0, 1, 2, 12, 13, 17, 18, 19, 44} {
+		if info.SupportedNIPs[i] != v {
+			t.Errorf("expected info.SupportedNIPs[%d] to equal %v, got %v",
+				i, v, info.SupportedNIPs)
+			return
+		}
+	}
+}
diff --git a/nip11/types.go b/nip11/types.go
index ae3ad2b..78b4062 100644
--- a/nip11/types.go
+++ b/nip11/types.go
@@ -1,5 +1,7 @@
 package nip11
 
+import "golang.org/x/exp/slices"
+
 type RelayInformationDocument struct {
 	Name          string `json:"name"`
 	Description   string `json:"description"`
@@ -19,6 +21,17 @@ type RelayInformationDocument struct {
 	Icon           string                   `json:"icon"`
 }
 
+func (info *RelayInformationDocument) AddSupportedNIP(number int) {
+	idx, exists := slices.BinarySearch(info.SupportedNIPs, number)
+	if exists {
+		return
+	}
+
+	info.SupportedNIPs = append(info.SupportedNIPs, -1)
+	copy(info.SupportedNIPs[idx+1:], info.SupportedNIPs[idx:])
+	info.SupportedNIPs[idx] = number
+}
+
 type RelayLimitationDocument struct {
 	MaxMessageLength int  `json:"max_message_length,omitempty"`
 	MaxSubscriptions int  `json:"max_subscriptions,omitempty"`