diff --git a/main/CMakeLists.txt b/main/CMakeLists.txt
index 2a6c8ae..2da29eb 100644
--- a/main/CMakeLists.txt
+++ b/main/CMakeLists.txt
@@ -15,6 +15,8 @@ idf_component_register(
   "uart_proto.c"
   "cmd_handler.c"
   "cmd_version.c"
+  "cmd_client_info.c"
+  "client_registry.c"
   "esp_now_comm.c"
   "proto/uart_messages.pb.c"
   "proto/pb_encode.c"
diff --git a/main/README.md b/main/README.md
index 1404310..bf0c194 100644
--- a/main/README.md
+++ b/main/README.md
@@ -28,7 +28,7 @@ ESP32-S3 firmware for Powerpod nodes. Master and slave devices run the **same bi
 | Master | Yes — command handler, protobuf replies | Broadcasts discover; collects slave info |
 | Slave  | No         | Responds to discover with slave info |
 
-Planned: master forwards aggregated `ClientInfo` to the PC over UART (`CLIENT_INFO` in `uart_messages.proto`).
+Master keeps a **client registry** (`client_registry.c`) of slaves seen via ESP-NOW. The PC can query it with the `CLIENT_INFO` UART command.
 
 ## Boot configuration
 
@@ -156,7 +156,7 @@ Host and master speak nanopb-encoded `UartMessage` inside UART frames (byte 0 =
 | ID | Name | Status |
 |----|------|--------|
 | 3 | `VERSION` | Implemented (`cmd_version.c`) |
-| 4 | `CLIENT_INFO` | Planned — slave list to PC |
+| 4 | `CLIENT_INFO` | Implemented (`cmd_client_info.c`) — slave list from registry |
 | 5 | `CLIENT_INPUT` | Planned |
 | 16–20 | OTA / ESP-NOW OTA | Planned |
 
@@ -182,6 +182,24 @@ Build embeds `POWERPOD_GIT_HASH` via `git rev-parse` in `main/CMakeLists.txt`.
 
 Encoding: `uart_send_uart_message()` in `uart_proto.c`.
 
+### CLIENT_INFO command
+
+**Request:** framed payload `04` only (`MessageType.CLIENT_INFO`).
+
+**Response:** payload `04` + nanopb `UartMessage` with `client_info_response.clients` — one `ClientInfo` per registered slave (from ESP-NOW `SLAVE_INFO`).
+
+Fields per client: `id`, `mac`, `version`, `available`, `used`, `last_ping`, `last_success_ping` (milliseconds since boot, updated on each `SLAVE_INFO`).
+
+## Client registry
+
+| API | Description |
+|-----|-------------|
+| `client_registry_init()` | Clear all slots (called from `esp_now_comm_init`) |
+| `client_registry_upsert(mac, id, version, …)` | Add or refresh client; updates ping timestamps |
+| `client_registry_count()` / `client_registry_at(i)` | Iterate for UART encoding |
+
+Slaves register when the master receives `SLAVE_INFO` on the matching network.
+
 ## Host tool (`goTool/`)
 
 Go CLI to test UART from a PC connected to the **master** only.
@@ -189,7 +207,8 @@ Go CLI to test UART from a PC connected to the **master** only.
 ```bash
 cd goTool
 go mod tidy
-go run . -port /dev/ttyUSB0
+go run . -port /dev/ttyUSB0 version
+go run . -port /dev/ttyUSB0 clients
 ```
 
 | Flag | Default | Description |
@@ -197,7 +216,10 @@ go run . -port /dev/ttyUSB0
 | `-port` | (required) | Serial device, e.g. `/dev/ttyUSB0` |
 | `-baud` | `921600` | Must match `UART_BAUD_RATE` |
 
-Sends VERSION, reads framed response, prints `version` and `git_hash`.
+| Command | Description |
+|---------|-------------|
+| `version` | Firmware version and git hash |
+| `clients` | Registered slaves from master client registry |
 
 Regenerate Go protobuf:
 
@@ -232,6 +254,8 @@ Target: ESP32-S3. Close serial monitor on the UART adapter port before running `
 | `uart_proto.c/h` | Encode/send `UartMessage` |
 | `cmd_handler.c/h` | Command queue and dispatch |
 | `cmd_version.c/h` | VERSION handler |
+| `cmd_client_info.c/h` | CLIENT_INFO handler |
+| `client_registry.c/h` | Registered slave table |
 | `led_ring.c/h` | LED digit display |
 | `proto/uart_messages.proto` | Protocol schema |
 | `proto/*.pb.c/h` | Generated nanopb |
diff --git a/main/client_registry.c b/main/client_registry.c
new file mode 100644
index 0000000..03dc969
--- /dev/null
+++ b/main/client_registry.c
@@ -0,0 +1,104 @@
+#include "client_registry.h"
+#include "freertos/FreeRTOS.h"
+#include "freertos/idf_additions.h"
+#include <string.h>
+
+typedef struct {
+  client_info_t info;
+  bool active;
+} client_slot_t;
+
+static client_slot_t s_clients[CLIENT_REGISTRY_MAX];
+
+static uint32_t now_ms(void) {
+  return (uint32_t)(xTaskGetTickCount() * portTICK_PERIOD_MS);
+}
+
+static bool mac_equal(const uint8_t *a, const uint8_t *b) {
+  return memcmp(a, b, CLIENT_MAC_LEN) == 0;
+}
+
+void client_registry_init(void) { memset(s_clients, 0, sizeof(s_clients)); }
+
+const client_info_t *
+client_registry_find_by_mac(const uint8_t mac[CLIENT_MAC_LEN]) {
+  if (mac == NULL) {
+    return NULL;
+  }
+  for (size_t i = 0; i < CLIENT_REGISTRY_MAX; i++) {
+    if (s_clients[i].active && mac_equal(s_clients[i].info.mac, mac)) {
+      return &s_clients[i].info;
+    }
+  }
+  return NULL;
+}
+
+esp_err_t client_registry_upsert(const uint8_t mac[CLIENT_MAC_LEN], uint32_t id,
+                                 uint32_t version, bool available, bool used,
+                                 bool *out_is_new) {
+  if (mac == NULL) {
+    return ESP_ERR_INVALID_ARG;
+  }
+
+  uint32_t ts = now_ms();
+  client_slot_t *slot = NULL;
+  bool is_new = false;
+
+  for (size_t i = 0; i < CLIENT_REGISTRY_MAX; i++) {
+    if (s_clients[i].active && mac_equal(s_clients[i].info.mac, mac)) {
+      slot = &s_clients[i];
+      break;
+    }
+  }
+
+  if (slot == NULL) {
+    for (size_t i = 0; i < CLIENT_REGISTRY_MAX; i++) {
+      if (!s_clients[i].active) {
+        slot = &s_clients[i];
+        slot->active = true;
+        memcpy(slot->info.mac, mac, CLIENT_MAC_LEN);
+        is_new = true;
+        break;
+      }
+    }
+    if (slot == NULL) {
+      return ESP_ERR_NO_MEM;
+    }
+  }
+
+  slot->info.id = id;
+  slot->info.version = version;
+  slot->info.available = available;
+  slot->info.used = used;
+  slot->info.last_ping = ts;
+  slot->info.last_success_ping = ts;
+
+  if (out_is_new != NULL) {
+    *out_is_new = is_new;
+  }
+  return ESP_OK;
+}
+
+size_t client_registry_count(void) {
+  size_t n = 0;
+  for (size_t i = 0; i < CLIENT_REGISTRY_MAX; i++) {
+    if (s_clients[i].active) {
+      n++;
+    }
+  }
+  return n;
+}
+
+const client_info_t *client_registry_at(size_t index) {
+  size_t n = 0;
+  for (size_t i = 0; i < CLIENT_REGISTRY_MAX; i++) {
+    if (!s_clients[i].active) {
+      continue;
+    }
+    if (n == index) {
+      return &s_clients[i].info;
+    }
+    n++;
+  }
+  return NULL;
+}
diff --git a/main/client_registry.h b/main/client_registry.h
new file mode 100644
index 0000000..fc093b7
--- /dev/null
+++ b/main/client_registry.h
@@ -0,0 +1,33 @@
+#ifndef CLIENT_REGISTRY_H
+#define CLIENT_REGISTRY_H
+
+#include "esp_err.h"
+#include <stdbool.h>
+#include <stddef.h>
+#include <stdint.h>
+
+#define CLIENT_REGISTRY_MAX 16
+#define CLIENT_MAC_LEN 6
+
+typedef struct {
+  uint32_t id;
+  bool available;
+  bool used;
+  uint8_t mac[CLIENT_MAC_LEN];
+  uint32_t last_ping;
+  uint32_t last_success_ping;
+  uint32_t version;
+} client_info_t;
+
+void client_registry_init(void);
+
+/** Register or refresh a client; sets last_ping and last_success_ping to now. */
+esp_err_t client_registry_upsert(const uint8_t mac[CLIENT_MAC_LEN], uint32_t id,
+                                 uint32_t version, bool available, bool used,
+                                 bool *out_is_new);
+
+size_t client_registry_count(void);
+const client_info_t *client_registry_at(size_t index);
+const client_info_t *client_registry_find_by_mac(const uint8_t mac[CLIENT_MAC_LEN]);
+
+#endif
diff --git a/main/cmd_client_info.c b/main/cmd_client_info.c
new file mode 100644
index 0000000..69c8a00
--- /dev/null
+++ b/main/cmd_client_info.c
@@ -0,0 +1,77 @@
+#include "client_registry.h"
+#include "cmd_client_info.h"
+#include "cmd_handler.h"
+#include "esp_log.h"
+#include "pb_encode.h"
+#include "uart_messages.pb.h"
+#include "uart_proto.h"
+
+static const char *TAG = "[CLIENT_INFO]";
+
+static bool encode_client_mac(pb_ostream_t *stream, const pb_field_t *field,
+                              void *const *arg) {
+  const uint8_t *mac = (const uint8_t *)*arg;
+  if (mac == NULL) {
+    return true;
+  }
+  if (!pb_encode_tag_for_field(stream, field)) {
+    return false;
+  }
+  return pb_encode_string(stream, mac, CLIENT_MAC_LEN);
+}
+
+static bool encode_clients_list(pb_ostream_t *stream, const pb_field_t *field,
+                              void *const *arg) {
+  (void)arg;
+
+  size_t count = client_registry_count();
+  for (size_t i = 0; i < count; i++) {
+    const client_info_t *client = client_registry_at(i);
+    if (client == NULL) {
+      continue;
+    }
+
+    alox_ClientInfo proto = alox_ClientInfo_init_zero;
+    proto.id = client->id;
+    proto.available = client->available;
+    proto.used = client->used;
+    proto.last_ping = client->last_ping;
+    proto.last_success_ping = client->last_success_ping;
+    proto.version = client->version;
+    proto.mac.funcs.encode = encode_client_mac;
+    proto.mac.arg = (void *)client->mac;
+
+    if (!pb_encode_tag_for_field(stream, field)) {
+      return false;
+    }
+    if (!pb_encode_submessage(stream, alox_ClientInfo_fields, &proto)) {
+      return false;
+    }
+  }
+  return true;
+}
+
+static void handle_client_info(const uint8_t *data, size_t len) {
+  (void)data;
+  (void)len;
+
+  alox_UartMessage response = alox_UartMessage_init_zero;
+  response.type = alox_MessageType_CLIENT_INFO;
+  response.which_payload = alox_UartMessage_client_info_response_tag;
+  response.payload.client_info_response.clients.funcs.encode =
+      encode_clients_list;
+  response.payload.client_info_response.clients.arg = NULL;
+
+  ESP_LOGI(TAG, "sending %u clients", (unsigned)client_registry_count());
+
+  if (uart_send_uart_message(&response) != ESP_OK) {
+    ESP_LOGE(TAG, "failed to send response");
+  }
+}
+
+void cmd_client_info_register(void) {
+  if (msg_register_handler(alox_MessageType_CLIENT_INFO, handle_client_info) !=
+      ESP_OK) {
+    ESP_LOGE(TAG, "register failed");
+  }
+}
diff --git a/main/cmd_client_info.h b/main/cmd_client_info.h
new file mode 100644
index 0000000..57abb81
--- /dev/null
+++ b/main/cmd_client_info.h
@@ -0,0 +1,6 @@
+#ifndef CMD_CLIENT_INFO_H
+#define CMD_CLIENT_INFO_H
+
+void cmd_client_info_register(void);
+
+#endif
diff --git a/main/esp_now_comm.c b/main/esp_now_comm.c
index bfbd320..afd9469 100644
--- a/main/esp_now_comm.c
+++ b/main/esp_now_comm.c
@@ -1,3 +1,4 @@
+#include "client_registry.h"
 #include "esp_now_comm.h"
 #include "esp_err.h"
 #include "esp_event.h"
@@ -20,8 +21,6 @@
 #define ESPNOW_MSG_DISCOVER 1
 #define ESPNOW_MSG_SLAVE_INFO 2
 #define ESPNOW_DISCOVER_INTERVAL_MS 500
-#define ESPNOW_MAX_SLAVES 16
-
 static const uint8_t ESPNOW_BCAST[ESP_NOW_ETH_ALEN] = {0xff, 0xff, 0xff,
                                                        0xff, 0xff, 0xff};
 
@@ -45,19 +44,9 @@ typedef struct __attribute__((packed)) {
   uint8_t used;
 } espnow_slave_info_packet_t;
 
-typedef struct {
-  uint8_t mac[ESP_NOW_ETH_ALEN];
-  uint32_t slave_id;
-  uint32_t version;
-  bool available;
-  bool used;
-  bool seen;
-} slave_entry_t;
-
 static app_config_t s_config;
 static uint8_t s_wifi_channel;
 static uint8_t s_own_mac[ESP_NOW_ETH_ALEN];
-static slave_entry_t s_slaves[ESPNOW_MAX_SLAVES];
 static bool s_slave_joined;
 static uint8_t s_master_mac[ESP_NOW_ETH_ALEN];
 
@@ -97,30 +86,6 @@ static esp_err_t ensure_peer(const uint8_t *mac) {
 
 static esp_err_t ensure_broadcast_peer(void) { return ensure_peer(ESPNOW_BCAST); }
 
-static slave_entry_t *find_slave(const uint8_t *mac) {
-  for (int i = 0; i < ESPNOW_MAX_SLAVES; i++) {
-    if (s_slaves[i].seen && mac_equal(s_slaves[i].mac, mac)) {
-      return &s_slaves[i];
-    }
-  }
-  return NULL;
-}
-
-static slave_entry_t *alloc_slave(const uint8_t *mac) {
-  slave_entry_t *existing = find_slave(mac);
-  if (existing != NULL) {
-    return existing;
-  }
-  for (int i = 0; i < ESPNOW_MAX_SLAVES; i++) {
-    if (!s_slaves[i].seen) {
-      memcpy(s_slaves[i].mac, mac, ESP_NOW_ETH_ALEN);
-      s_slaves[i].seen = true;
-      return &s_slaves[i];
-    }
-  }
-  return NULL;
-}
-
 static void send_slave_info(const uint8_t *dest_mac) {
   espnow_slave_info_packet_t pkt = {
       .magic = ESPNOW_MAGIC,
@@ -169,22 +134,19 @@ static void handle_slave_info(const espnow_slave_info_packet_t *pkt) {
     return;
   }
 
-  bool is_new = (find_slave(pkt->mac) == NULL);
-  slave_entry_t *entry = alloc_slave(pkt->mac);
-  if (entry == NULL) {
-    ESP_LOGW(TAG, "slave table full");
+  bool is_new = false;
+  esp_err_t err = client_registry_upsert(
+      pkt->mac, pkt->slave_id, pkt->version, pkt->available != 0,
+      pkt->used != 0, &is_new);
+  if (err != ESP_OK) {
+    ESP_LOGW(TAG, "client registry full");
     return;
   }
 
-  entry->slave_id = pkt->slave_id;
-  entry->version = pkt->version;
-  entry->available = pkt->available != 0;
-  entry->used = pkt->used != 0;
-
   char mac_str[18];
   mac_to_str(pkt->mac, mac_str, sizeof(mac_str));
   if (is_new) {
-    ESP_LOGI(TAG, "slave joined id=%lu mac=%s ver=%lu",
+    ESP_LOGI(TAG, "client registered id=%lu mac=%s ver=%lu",
              (unsigned long)pkt->slave_id, mac_str,
              (unsigned long)pkt->version);
   }
@@ -278,7 +240,7 @@ esp_err_t esp_now_comm_init(const app_config_t *config) {
 
   memset(&s_config, 0, sizeof(s_config));
   memcpy(&s_config, config, sizeof(s_config));
-  memset(s_slaves, 0, sizeof(s_slaves));
+  client_registry_init();
   s_slave_joined = false;
   memset(s_master_mac, 0, sizeof(s_master_mac));
 
diff --git a/main/powerpod.c b/main/powerpod.c
index 8eee094..3886839 100644
--- a/main/powerpod.c
+++ b/main/powerpod.c
@@ -1,5 +1,6 @@
 #include "app_config.h"
 #include "cmd_handler.h"
+#include "cmd_client_info.h"
 #include "cmd_version.h"
 #include "esp_now_comm.h"
 #include "powerpod.h"
@@ -133,6 +134,7 @@ void app_main(void) {
     init_cmdHandler(cmd_queue);
     init_uart(cmd_queue);
     cmd_version_register();
+    cmd_client_info_register();
   }
 
   uint8_t current_digit = 10;