diff --git a/toxcore/Messenger.c b/toxcore/Messenger.c
index c45debed47..92cbb1d36a 100644
--- a/toxcore/Messenger.c
+++ b/toxcore/Messenger.c
@@ -158,6 +158,15 @@ static int send_online_packet(Messenger *m, int32_t friendnumber)
         return 0;
     }
 
+    uint8_t buf[TOX_CAPABILITIES_SIZE + 1];
+    buf[0] = PACKET_ID_ONLINE;
+    net_pack_u64(buf + 1, TOX_CAPABILITIES_CURRENT);
+
+    if (write_cryptpacket(m->net_crypto, friend_connection_crypt_connection_id(m->fr_c,
+                          m->friendlist[friendnumber].friendcon_id), buf, TOX_CAPABILITIES_SIZE + 1, 0) == -1) {
+        return -1;
+    }
+
     uint8_t packet = PACKET_ID_ONLINE;
     return write_cryptpacket(m->net_crypto, friend_connection_crypt_connection_id(m->fr_c,
                              m->friendlist[friendnumber].friendcon_id), &packet, sizeof(packet), 0) != -1;
@@ -202,6 +211,7 @@ static int32_t init_new_friend(Messenger *m, const uint8_t *real_pk, uint8_t sta
             m->friendlist[i].userstatus = USERSTATUS_NONE;
             m->friendlist[i].is_typing = 0;
             m->friendlist[i].message_id = 0;
+            m->friendlist[i].toxcore_capabilities = TOX_CAPABILITY_BASIC;
             friend_connection_callbacks(m->fr_c, friendcon_id, MESSENGER_CALLBACK_INDEX, &m_handle_status, &m_handle_packet,
                                         &m_handle_lossy_packet, m, i);
 
@@ -2157,6 +2167,19 @@ static int m_handle_status(void *object, int i, uint8_t status, void *userdata)
     return 0;
 }
 
+/* get capabilities of friend's toxcore
+ * return TOX_CAPABILITY_BASIC on any error
+ */
+uint64_t m_get_friend_toxcore_capabilities(const Messenger *m, int32_t friendnumber)
+{
+    if (friend_not_valid(m, friendnumber)) {
+        return TOX_CAPABILITY_BASIC;
+    }
+
+    // return toxcore_capabilities for friend, not matter if ONLINE or OFFLINE
+    return m->friendlist[friendnumber].toxcore_capabilities;
+}
+
 static int m_handle_packet(void *object, int i, const uint8_t *temp, uint16_t len, void *userdata)
 {
     if (len == 0) {
@@ -2169,9 +2192,17 @@ static int m_handle_packet(void *object, int i, const uint8_t *temp, uint16_t le
     uint32_t data_length = len - 1;
 
     if (m->friendlist[i].status != FRIEND_ONLINE) {
-        if (packet_id == PACKET_ID_ONLINE && len == 1) {
-            set_friend_status(m, i, FRIEND_ONLINE, userdata);
-            send_online_packet(m, i);
+        if (packet_id == PACKET_ID_ONLINE) {
+            if (data_length == TOX_CAPABILITIES_SIZE) {
+                uint64_t received_caps;
+                net_unpack_u64(data, &received_caps);
+                m->friendlist[i].toxcore_capabilities = received_caps;
+            } else if (data_length == 0) {
+                set_friend_status(m, i, FRIEND_ONLINE, userdata);
+                send_online_packet(m, i);
+            } else {
+                return -1;
+            }
         } else {
             return -1;
         }
diff --git a/toxcore/Messenger.h b/toxcore/Messenger.h
index cd872a2d24..8da0238722 100644
--- a/toxcore/Messenger.h
+++ b/toxcore/Messenger.h
@@ -64,6 +64,31 @@ typedef struct Messenger_Options {
     void *log_user_data;
 } Messenger_Options;
 
+/* this means no special capabilities, in other words clients that are older
+ * and did not implement this feature yet
+ */
+#define TOX_CAPABILITY_BASIC 0
+
+/* ATTENTION: if you are adding new flags in your fork or toxcore,
+ * or in c-toxcore master,
+ * please coordinate with us first!
+ * thank you, the Tox Devs.
+ */
+#define TOX_CAPABILITY_CAPABILITIES ((uint64_t)1) << 0
+/* add new flags/bits here */
+
+/* if the TOX_CAPABILITY_NEXT_IMPLEMENTATION flag is set it means
+ * we are using a different system for indicating capabilities now,
+ * and TOX_CAPABILITIES_* should be ignored and just the new (not yet known)
+ * system should be used
+ */
+#define TOX_CAPABILITY_NEXT_IMPLEMENTATION ((uint64_t)1) << 63
+
+/* hardcoded capabilities of this version/branch of toxcore */
+#define TOX_CAPABILITIES_CURRENT (uint64_t)(TOX_CAPABILITY_CAPABILITIES)
+/* size of the FLAGS in bytes */
+#define TOX_CAPABILITIES_SIZE sizeof(uint64_t)
+
 
 struct Receipts {
     uint32_t packet_num;
@@ -228,6 +253,7 @@ typedef struct Friend {
 
     struct Receipts *receipts_start;
     struct Receipts *receipts_end;
+    uint64_t toxcore_capabilities;
 } Friend;
 
 struct Messenger {
@@ -460,6 +486,11 @@ uint8_t m_get_userstatus(const Messenger *m, int32_t friendnumber);
 uint8_t m_get_self_userstatus(const Messenger *m);
 
 
+/* get capabilities of friend's toxcore
+ * return TOX_CAPABILITY_BASIC on any error
+ */
+uint64_t m_get_friend_toxcore_capabilities(const Messenger *m, int32_t friendnumber);
+
 /* returns timestamp of last time friendnumber was seen online or 0 if never seen.
  * if friendnumber is invalid this function will return UINT64_MAX.
  */