diff --git a/internal/mcp/jsonrpc.go b/internal/mcp/jsonrpc.go
new file mode 100644
index 0000000..e25f191
--- /dev/null
+++ b/internal/mcp/jsonrpc.go
@@ -0,0 +1,43 @@
+package mcp
+
+import "encoding/json"
+
+const (
+	CodePermissionDenied = -32001
+	CodeNotFound         = -32002
+	CodeConflict         = -32003
+	CodeValidation       = -32004
+	CodeUpstreamGitea    = -32005
+)
+
+type Request struct {
+	JSONRPC string          `json:"jsonrpc"`
+	ID      any             `json:"id,omitempty"`
+	Method  string          `json:"method"`
+	Params  json.RawMessage `json:"params,omitempty"`
+}
+
+type Response struct {
+	JSONRPC string    `json:"jsonrpc"`
+	ID      any       `json:"id,omitempty"`
+	Result  any       `json:"result,omitempty"`
+	Error   *RPCError `json:"error,omitempty"`
+}
+
+type RPCError struct {
+	Code    int    `json:"code"`
+	Message string `json:"message"`
+	Data    any    `json:"data,omitempty"`
+}
+
+func NewResponse(id any, result any) Response {
+	return Response{JSONRPC: "2.0", ID: id, Result: result}
+}
+
+func NewErrorResponse(id any, code int, msg string, data any) Response {
+	return Response{
+		JSONRPC: "2.0",
+		ID:      id,
+		Error:   &RPCError{Code: code, Message: msg, Data: data},
+	}
+}
diff --git a/internal/mcp/jsonrpc_test.go b/internal/mcp/jsonrpc_test.go
new file mode 100644
index 0000000..6242f7c
--- /dev/null
+++ b/internal/mcp/jsonrpc_test.go
@@ -0,0 +1,26 @@
+package mcp_test
+
+import (
+	"encoding/json"
+	"testing"
+
+	"gitea.d-ma.be/mathias/gitea-mcp/internal/mcp"
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+)
+
+func TestRequestUnmarshal(t *testing.T) {
+	raw := []byte(`{"jsonrpc":"2.0","id":1,"method":"initialize","params":{}}`)
+	var req mcp.Request
+	require.NoError(t, json.Unmarshal(raw, &req))
+	assert.Equal(t, "2.0", req.JSONRPC)
+	assert.Equal(t, "initialize", req.Method)
+}
+
+func TestErrorResponseShape(t *testing.T) {
+	resp := mcp.NewErrorResponse(1, mcp.CodePermissionDenied, "no", nil)
+	b, _ := json.Marshal(resp)
+	assert.JSONEq(t,
+		`{"jsonrpc":"2.0","id":1,"error":{"code":-32001,"message":"no"}}`,
+		string(b))
+}