diff --git a/tools/etcpmon/Makefile b/tools/etcpmon/Makefile
index 8383d035..7f40e719 100644
--- a/tools/etcpmon/Makefile
+++ b/tools/etcpmon/Makefile
@@ -16,7 +16,7 @@ TARGET = etcpmon.exe
 SRCS = etcpmon_main.c etcpmon_gui.c etcpmon_client.c etcpmon_graph.c
 OBJS = $(SRCS:.c=.o)
 
-.PHONY: all clean rebuild
+.PHONY: all clean rebuild check
 
 all: $(TARGET)
 
@@ -28,8 +28,14 @@ $(TARGET): $(OBJS)
 	@echo Compiling $<
 	$(CC) $(CFLAGS) -c -o $@ $<
 
+test_etcpmon.exe: test_etcpmon.c $(SRCS) $(wildcard *.h)
+	$(CC) $(CFLAGS) -o $@ test_etcpmon.c etcpmon_graph.c $(LIBS)
+
+check: test_etcpmon.exe
+	$(TEST_RUNNER) ./test_etcpmon.exe
+
 clean:
 	@echo Cleaning...
-	rm -f $(OBJS) $(TARGET)
+	rm -f $(OBJS) $(TARGET) test_etcpmon.exe
 
 rebuild: clean $(TARGET)
diff --git a/tools/etcpmon/test_etcpmon.c b/tools/etcpmon/test_etcpmon.c
new file mode 100644
index 00000000..b3b2367d
--- /dev/null
+++ b/tools/etcpmon/test_etcpmon.c
@@ -0,0 +1,212 @@
+/* Регрессии опроса и выбора connections на настоящих Winsock/WinAPI. */
+#include <assert.h>
+
+/* Проверяем также внутренние callbacks без расширения публичного API. */
+#include "etcpmon_client.c"
+#include "etcpmon_gui.c"
+
+static SOCKET listener;
+static SOCKET server_sock;
+static struct etcpmon_client client;
+static struct etcpmon_app app;
+static int callbacks;
+
+static void request_callback(void* arg, uint8_t type, const uint8_t* payload, uint16_t size) {
+    (void)arg; (void)type; (void)payload; (void)size;
+    callbacks++;
+}
+
+/* Соединяем клиент с локальным сервером, не обращаясь к реальному uTun. */
+static void connect_client(void) {
+    struct sockaddr_in addr;
+    int len = sizeof(addr);
+    assert(getsockname(listener, (struct sockaddr*)&addr, &len) == 0);
+    assert(etcpmon_client_connect(&client, "127.0.0.1", ntohs(addr.sin_port)) == 0);
+    for (int i = 0; i < 1000 && !client.fully_connected; i++) {
+        assert(etcpmon_client_process(&client) >= 0);
+        Sleep(1);
+    }
+    assert(client.fully_connected);
+    server_sock = accept(listener, NULL, NULL);
+    assert(server_sock != INVALID_SOCKET);
+    u_long nonblock = 1;
+    assert(ioctlsocket(server_sock, FIONBIO, &nonblock) == 0);
+    app.need_initial_request = 1;
+}
+
+/* Разбираем реальные команды в TCP-потоке и считаем запросы нужного типа. */
+static int drain_commands(uint8_t type) {
+    static uint8_t buffer[ETCPMON_MAX_MSG_SIZE];
+    static int used;
+    int count = 0;
+    for (int i = 0; i < 100; i++) {
+        int got = recv(server_sock, (char*)buffer + used, sizeof(buffer) - used, 0);
+        if (got == SOCKET_ERROR) {
+            assert(WSAGetLastError() == WSAEWOULDBLOCK);
+            if (count) break;
+            Sleep(1);
+            continue;
+        }
+        assert(got > 0);
+        used += got;
+        while (used >= (int)sizeof(struct etcpmon_msg_header)) {
+            struct etcpmon_msg_header* hdr = (struct etcpmon_msg_header*)buffer;
+            assert(etcpmon_validate_header(hdr) == 0);
+            if (used < hdr->size) break;
+            if (hdr->type == type) count++;
+            int size = hdr->size;
+            memmove(buffer, buffer + size, used - size);
+            used -= size;
+        }
+    }
+    assert(used == 0);
+    return count;
+}
+
+/* Доставляем снимок списка через TCP, в том числе двумя отдельными фрагментами. */
+static void deliver_list(struct etcpmon_conn_info* list, uint8_t count) {
+    uint8_t buffer[ETCPMON_CONN_LIST_SIZE(3)];
+    assert(count <= 3);
+    uint16_t size = (uint16_t)ETCPMON_CONN_LIST_SIZE(count);
+    etcpmon_build_header((struct etcpmon_msg_header*)buffer, size - sizeof(struct etcpmon_msg_header), ETCPMON_RSP_CONN_LIST, 0);
+    buffer[sizeof(struct etcpmon_msg_header)] = count;
+    if (count) memcpy(buffer + sizeof(struct etcpmon_msg_header) + 1, list, count * sizeof(*list));
+    assert(send(server_sock, (const char*)buffer, 2, 0) == 2);
+    assert(etcpmon_client_process(&client) >= 0);
+    assert(send(server_sock, (const char*)buffer + 2, size - 2, 0) == size - 2);
+    int received = 0;
+    for (int i = 0; i < 1000 && !received; i++) {
+        int result = etcpmon_client_process(&client);
+        assert(result >= 0);
+        received += result;
+        Sleep(1);
+    }
+    assert(received == 1);
+    assert(client.conn_count == count);
+    assert(SendMessage(app.hListConnections, LB_GETCOUNT, 0, 0) == count);
+}
+
+int main(void) {
+    WSADATA data;
+    assert(WSAStartup(MAKEWORD(2, 2), &data) == 0);
+    listener = socket(AF_INET, SOCK_STREAM, IPPROTO_TCP);
+    assert(listener != INVALID_SOCKET);
+    struct sockaddr_in addr = {0};
+    addr.sin_family = AF_INET;
+    addr.sin_addr.s_addr = htonl(INADDR_LOOPBACK);
+    assert(bind(listener, (struct sockaddr*)&addr, sizeof(addr)) == 0);
+    assert(listen(listener, 1) == 0);
+    etcpmon_client_init(&client);
+    client.log_file = fopen("test_etcpmon.log", "w");
+    assert(client.log_file);
+    app.client = &client;
+    app.hWndMain = CreateWindowExA(0, "STATIC", "etcpmon regression", WS_OVERLAPPEDWINDOW,
+                                  0, 0, 500, 300, NULL, NULL, GetModuleHandle(NULL), NULL);
+    assert(app.hWndMain);
+    app.hListConnections = CreateWindowExA(0, "LISTBOX", "", WS_CHILD | LBS_NOTIFY,
+        0, 0, 400, 100, app.hWndMain, (HMENU)IDC_LIST_CONNECTIONS, GetModuleHandle(NULL), NULL);
+    app.hListSockets = CreateWindowExA(0, "LISTBOX", "", WS_CHILD,
+        0, 100, 400, 100, app.hWndMain, (HMENU)IDC_LIST_SOCKETS, GetModuleHandle(NULL), NULL);
+    assert(app.hListConnections && app.hListSockets);
+    etcpmon_client_set_callbacks(&client, on_connected, on_disconnected, on_conn_list,
+        on_socket_list, on_metrics, on_error, NULL, &app);
+    connect_client();
+
+    puts("Initial and periodic polling while connections are empty");
+    OnTimer(&app);
+    assert(drain_commands(ETCPMON_CMD_LIST_CONN) == 1);
+    deliver_list(NULL, 0);
+    Sleep(LIST_UPDATE_INTERVAL + 10);
+    OnTimer(&app);
+    assert(drain_commands(ETCPMON_CMD_LIST_CONN) == 1);
+
+    puts("Appearance, manual selection, reorder and rename preserve the full peer ID");
+    struct etcpmon_conn_info list[3] = {
+        {0x123456789ABCDEF0ULL, "first"}, {0xFEDCBA9876543210ULL, "second"}, {3, "third"}
+    };
+    deliver_list(list, 2);
+    assert(client.selected_peer_id == list[0].peer_node_id);
+    SendMessage(app.hListConnections, LB_SETCURSEL, 1, 0);
+    OnConnectionSelect(&app);
+    assert(client.selected_peer_id == list[1].peer_node_id);
+    struct etcpmon_conn_info reordered[3] = {list[1], list[2], list[0]};
+    strcpy(reordered[0].name, "renamed");
+    deliver_list(reordered, 3);
+    assert(client.selected_peer_id == list[1].peer_node_id);
+    assert(SendMessage(app.hListConnections, LB_GETCURSEL, 0, 0) == 0);
+    deliver_list(reordered, 3);
+    assert(client.selected_peer_id == list[1].peer_node_id);
+
+    puts("Removal selects a surviving peer; stale metrics are ignored; each sample is stored once");
+    deliver_list(&list[2], 1);
+    assert(client.selected_peer_id == 3);
+    struct etcpmon_rsp_metrics metrics = {0};
+    metrics.etcp.peer_node_id = list[1].peer_node_id;
+    handle_response(&client, ETCPMON_RSP_METRICS, (const uint8_t*)&metrics, sizeof(metrics));
+    assert(client.history.count == 0);
+    metrics.etcp.peer_node_id = 3;
+    handle_response(&client, ETCPMON_RSP_METRICS, (const uint8_t*)&metrics, sizeof(metrics));
+    assert(client.history.count == 1 && client.last_links_count == 0);
+
+    puts("Empty snapshots clear connections, metrics, graph and sockets");
+    deliver_list(NULL, 0);
+    assert(client.selected_peer_id == 0 && app.last_selected_peer_id == 0);
+    assert(client.history.count == 0 && client.last_metrics == NULL && client.conn_list == NULL);
+    SendMessageA(app.hListSockets, LB_ADDSTRING, 0, (LPARAM)"old socket");
+    const uint8_t empty[] = {0};
+    handle_response(&client, ETCPMON_RSP_SOCKET_LIST, empty, sizeof(empty));
+    assert(SendMessage(app.hListSockets, LB_GETCOUNT, 0, 0) == 0);
+
+    puts("Removing the queue tail keeps earlier requests linked; seq IDs cannot collide");
+    struct etcpmon_pending_request* first = client.pending_head;
+    assert(first); /* Начальный запрос debug config пока без ответа. */
+    assert(etcpmon_client_send_request(&client, ETCPMON_CMD_ACTION, NULL, 0, request_callback, NULL) == 0);
+    uint8_t last_seq = client.pending_tail->seq_id;
+    uint8_t error_payload[] = {ETCPMON_ERR_INVALID_CMD, 't', 'e', 's', 't', 0};
+    client.last_response_seq_id = last_seq;
+    handle_response_with_callback(&client, ETCPMON_RSP_ERROR, error_payload, sizeof(error_payload));
+    assert(client.pending_tail != NULL && client.pending_tail->next == NULL && callbacks == 1);
+    client.next_seq_id = first->seq_id;
+    assert(etcpmon_client_send_request(&client, ETCPMON_CMD_ACTION, NULL, 0, request_callback, NULL) == 0);
+    assert(first->next && client.pending_tail->seq_id != first->seq_id);
+    struct etcpmon_pending_request* old_tail = client.pending_tail;
+    assert(etcpmon_client_send_request(&client, ETCPMON_CMD_ACTION, NULL, ETCPMON_MAX_MSG_SIZE, request_callback, NULL) == -1);
+    assert(client.pending_tail == old_tail && old_tail->next == NULL);
+
+    puts("Disconnect and reconnect reset selection and request the initial snapshots again");
+    OnDisconnect(&app);
+    assert(client.conn_list == NULL && client.pending_head == NULL && app.need_initial_request);
+    closesocket(server_sock);
+    connect_client();
+    OnTimer(&app);
+    assert(drain_commands(ETCPMON_CMD_LIST_CONN) == 1);
+    deliver_list(&list[0], 1);
+    assert(client.selected_peer_id == list[0].peer_node_id);
+
+    puts("Slow metrics responses cannot accumulate requests; response timeout clears state");
+    assert(etcpmon_client_process(&client) >= 0);
+    int pending_metrics = 0;
+    for (struct etcpmon_pending_request* req = client.pending_head; req; req = req->next) {
+        if (req->type == ETCPMON_CMD_GET_METRICS) pending_metrics++;
+    }
+    assert(pending_metrics == 1);
+    Sleep(ETCPMON_UPDATE_INTERVAL_MS + 10);
+    assert(etcpmon_client_process(&client) >= 0);
+    pending_metrics = 0;
+    for (struct etcpmon_pending_request* req = client.pending_head; req; req = req->next) {
+        if (req->type == ETCPMON_CMD_GET_METRICS) pending_metrics++;
+    }
+    assert(pending_metrics == 1);
+    client.pending_head->sent_at = GetTickCount() - REQUEST_TIMEOUT_MS;
+    assert(etcpmon_client_process(&client) == -1);
+    assert(client.pending_head == NULL && !client.connected && app.need_initial_request);
+    assert(SendMessage(app.hListConnections, LB_GETCOUNT, 0, 0) == 0);
+
+    etcpmon_client_cleanup(&client);
+    closesocket(server_sock);
+    closesocket(listener);
+    DestroyWindow(app.hWndMain);
+    WSACleanup();
+    puts("PASS: etcpmon polling, selection, snapshots, queue and reconnect regressions");
+    return 0;
+}