diff --git a/protocol/protocol.go b/protocol/protocol.go
new file mode 100644
index 0000000..a182fe3
--- /dev/null
+++ b/protocol/protocol.go
@@ -0,0 +1,76 @@
+package protocol
+
+// > identify
+type IdRequest struct {
+	Type       string `json:"type"`
+	AssignedID string `json:"id"`
+}
+
+func NewIdRequest(id string) *IdRequest {
+	return &IdRequest{
+		Type:       "idreq",
+		AssignedID: id,
+	}
+}
+
+// < [robot | spectator], name, client-type, game ID
+type ClientID struct {
+	Type      string `json:"type"`
+	Name      string `json:"name"`
+	Useragent string `json:"useragent"`
+}
+
+func (c *ClientID) Valid() (bool, string) {
+	switch c.Type {
+	case "robot", "spectator":
+		return true, ""
+	}
+	return false, "usergent must be 'robot' or 'spectator'"
+}
+
+type BoardSize struct {
+	Width  float64 `json:"width"`
+	Height float64 `json:"height"`
+}
+
+type GameParam struct {
+	BoardSize BoardSize `json:"boardsize"`
+	Type      string    `json:"type"`
+}
+
+// > [OK | FULL | NOT AUTH], board size, game params
+func NewGameParam(w, h float64) *GameParam {
+	return &GameParam{
+		BoardSize: BoardSize{
+			Width:  w,
+			Height: h,
+		},
+		Type: "gameparam",
+	}
+}
+
+type Handshake struct {
+	ID      string `json:"id"`
+	Success bool   `json:"success"`
+	Type    string `json:"type"`
+}
+
+func NewHandshake(id string, success bool) *Handshake {
+	return &Handshake{
+		ID:      id,
+		Success: success,
+		Type:    "handshake",
+	}
+}
+
+type Failure struct {
+	Reason string `json:"reason"`
+	Type   string `json:"type"`
+}
+
+func NewFailure(reason string) *Failure {
+	return &Failure{
+		Reason: reason,
+		Type:   "failure",
+	}
+}
diff --git a/protocol/protocol_test.go b/protocol/protocol_test.go
new file mode 100644
index 0000000..da25620
--- /dev/null
+++ b/protocol/protocol_test.go
@@ -0,0 +1,45 @@
+package protocol
+
+import (
+	"encoding/json"
+	"testing"
+)
+
+type result struct {
+	b   bool
+	msg string
+}
+type clientIDTest struct {
+	clientid ClientID
+	expected result
+}
+
+var clientIDTests = []clientIDTest{
+	{ClientID{Type: "robot"}, result{true, ""}},
+	{ClientID{Type: "spectator"}, result{true, ""}},
+	{ClientID{Type: "schmarglenoggler"}, result{false, "usergent must be 'robot' or 'spectator'"}},
+}
+
+func TestClientIDs(t *testing.T) {
+	for _, tt := range clientIDTests {
+		v, msg := tt.clientid.Valid()
+		actual := result{v, msg}
+		if actual.b != tt.expected.b || actual.msg != tt.expected.msg {
+			t.Errorf("%+v: expected %v, actual %v", tt.clientid, tt.expected, actual)
+		}
+	}
+}
+
+func TestClientIDParse(t *testing.T) {
+	var s ClientID
+	err := json.Unmarshal(
+		[]byte(`{
+            "type": "robot",
+            "name": "dummy",
+            "id": "24601",
+            "useragent": "gorobots.js"
+        }`), &s)
+	if err != nil {
+		t.Errorf("fail to parse: %v", err)
+	}
+}