diff --git a/src/core/diags/README.md b/src/core/diags/README.md
index 3db8fae04..127757794 100644
--- a/src/core/diags/README.md
+++ b/src/core/diags/README.md
@@ -38,7 +38,7 @@ Start diagnostics mode.
 ```bash
 > diag start
 start diagnostics mode
-status 0x00
+Done
 ```
 
 ### diag channel
@@ -48,6 +48,7 @@ Get the IEEE 802.15.4 Channel value for diagnostics module.
 ```bash
 > diag channel
 channel: 11
+Done
 ```
 
 ### diag channel \<channel\>
@@ -57,7 +58,7 @@ Set the IEEE 802.15.4 Channel value for diagnostics module.
 ```bash
 > diag channel 11
 set channel to 11
-status 0x00
+Done
 ```
 
 ### diag cw start
@@ -123,6 +124,7 @@ Get the tx power value(dBm) for diagnostics module.
 ```bash
 > diag power
 tx power: -10 dBm
+Done
 ```
 
 ### diag power \<power\>
@@ -132,7 +134,7 @@ Set the tx power value(dBm) for diagnostics module.
 ```bash
 > diag power -10
 set tx power to -10 dBm
-status 0x00
+Done
 ```
 
 ### diag powersettings
@@ -173,7 +175,7 @@ Send the frame set by `diag frame` if length is omitted. Otherwise overwrite the
 ```bash
 > diag send 20 100
 sending 0x14 packet(s), length 0x64
-status 0x00
+Done
 ```
 
 ### diag repeat \<delay\> [length]
@@ -185,7 +187,7 @@ Send the frame set by `diag frame` if length is omitted. Otherwise overwrite the
 ```bash
 > diag repeat 100 100
 sending packets of length 0x64 at the delay of 0x64 ms
-status 0x00
+Done
 ```
 
 ### diag repeat stop
@@ -195,7 +197,7 @@ Stop repeated packet transmission.
 ```bash
 > diag repeat stop
 repeated packet transmission is stopped
-status 0x00
+Done
 ```
 
 ### diag radio sleep
@@ -205,7 +207,7 @@ Enter radio sleep mode.
 ```bash
 > diag radio sleep
 set radio from receive to sleep
-status 0x00
+Done
 ```
 
 ### diag radio receive
@@ -215,7 +217,7 @@ Set radio from sleep mode to receive mode.
 ```bash
 > diag radio receive
 set radio from sleep to receive on channel 11
-status 0x00
+Done
 ```
 
 ### diag radio receive \[async\] \<number\> \[lpr\]
@@ -245,6 +247,7 @@ Return the state of the radio.
 ```bash
 > diag radio state
 sleep
+Done
 ```
 
 ### diag radio enable
@@ -312,6 +315,7 @@ received packets: 10
 sent packets: 10
 first received packet: rssi=-65, lqi=101
 last received packet: rssi=-64, lqi=98
+Done
 ```
 
 ### diag stats clear
@@ -321,6 +325,7 @@ Clear statistics during diagnostics mode.
 ```bash
 > diag stats clear
 stats cleared
+Done
 ```
 
 ### diag gpio get \<gpio\>
@@ -384,7 +389,7 @@ first received packet: rssi=-65, lqi=101
 last received packet: rssi=-61, lqi=98
 
 stop diagnostics mode
-status 0x00
+Done
 ```
 
 ### diag rcp
diff --git a/src/core/diags/factory_diags.cpp b/src/core/diags/factory_diags.cpp
index 2048d1c3b..09ea38a3d 100644
--- a/src/core/diags/factory_diags.cpp
+++ b/src/core/diags/factory_diags.cpp
@@ -93,7 +93,6 @@ Error Diags::ProcessChannel(uint8_t aArgsLength, char *aArgs[])
     otPlatDiagChannelSet(channel);
 
 exit:
-    AppendErrorResult(error);
     return error;
 }
 
@@ -109,7 +108,6 @@ Error Diags::ProcessPower(uint8_t aArgsLength, char *aArgs[])
     otPlatDiagTxPowerSet(power);
 
 exit:
-    AppendErrorResult(error);
     return error;
 }
 
@@ -148,7 +146,6 @@ Error Diags::ProcessEcho(uint8_t aArgsLength, char *aArgs[])
     }
 
 exit:
-    AppendErrorResult(error);
     return error;
 }
 
@@ -326,7 +323,6 @@ Error Diags::ProcessFrame(uint8_t aArgsLength, char *aArgs[])
     mIsTxPacketSet                                 = true;
 
 exit:
-    AppendErrorResult(error);
     return error;
 }
 
@@ -334,8 +330,6 @@ Error Diags::ProcessChannel(uint8_t aArgsLength, char *aArgs[])
 {
     Error error = kErrorNone;
 
-    VerifyOrExit(otPlatDiagModeGet(), error = kErrorInvalidState);
-
     if (aArgsLength == 0)
     {
         Output("channel: %d\r\n", mChannel);
@@ -351,11 +345,10 @@ Error Diags::ProcessChannel(uint8_t aArgsLength, char *aArgs[])
         IgnoreError(Get<Radio>().Receive(mChannel));
         otPlatDiagChannelSet(mChannel);
 
-        Output("set channel to %d\r\nstatus 0x%02x\r\n", mChannel, error);
+        Output("set channel to %d\r\n", mChannel);
     }
 
 exit:
-    AppendErrorResult(error);
     return error;
 }
 
@@ -363,8 +356,6 @@ Error Diags::ProcessPower(uint8_t aArgsLength, char *aArgs[])
 {
     Error error = kErrorNone;
 
-    VerifyOrExit(otPlatDiagModeGet(), error = kErrorInvalidState);
-
     if (aArgsLength == 0)
     {
         Output("tx power: %d dBm\r\n", mTxPower);
@@ -379,11 +370,10 @@ Error Diags::ProcessPower(uint8_t aArgsLength, char *aArgs[])
         SuccessOrExit(error = Get<Radio>().SetTransmitPower(mTxPower));
         otPlatDiagTxPowerSet(mTxPower);
 
-        Output("set tx power to %d dBm\r\nstatus 0x%02x\r\n", mTxPower, error);
+        Output("set tx power to %d dBm\r\n", mTxPower);
     }
 
 exit:
-    AppendErrorResult(error);
     return error;
 }
 
@@ -391,14 +381,13 @@ Error Diags::ProcessRepeat(uint8_t aArgsLength, char *aArgs[])
 {
     Error error = kErrorNone;
 
-    VerifyOrExit(otPlatDiagModeGet(), error = kErrorInvalidState);
     VerifyOrExit(aArgsLength > 0, error = kErrorInvalidArgs);
 
     if (StringMatch(aArgs[0], "stop"))
     {
         otPlatAlarmMilliStop(&GetInstance());
         mRepeatActive = false;
-        Output("repeated packet transmission is stopped\r\nstatus 0x%02x\r\n", error);
+        Output("repeated packet transmission is stopped\r\n");
     }
     else
     {
@@ -431,12 +420,11 @@ Error Diags::ProcessRepeat(uint8_t aArgsLength, char *aArgs[])
         mRepeatActive = true;
         uint32_t now  = otPlatAlarmMilliGetNow();
         otPlatAlarmMilliStartAt(&GetInstance(), now, mTxPeriod);
-        Output("sending packets of length %#x at the delay of %#x ms\r\nstatus 0x%02x\r\n", static_cast<int>(mTxLen),
-               static_cast<int>(mTxPeriod), error);
+        Output("sending packets of length %#x at the delay of %#x ms\r\n", static_cast<int>(mTxLen),
+               static_cast<int>(mTxPeriod));
     }
 
 exit:
-    AppendErrorResult(error);
     return error;
 }
 
@@ -446,7 +434,6 @@ Error Diags::ProcessSend(uint8_t aArgsLength, char *aArgs[])
     uint32_t txPackets;
     uint8_t  txLength;
 
-    VerifyOrExit(otPlatDiagModeGet(), error = kErrorInvalidState);
     VerifyOrExit(aArgsLength >= 1, error = kErrorInvalidArgs);
 
     SuccessOrExit(error = Utils::CmdLineParser::ParseAsUint32(aArgs[0], txPackets));
@@ -470,12 +457,10 @@ Error Diags::ProcessSend(uint8_t aArgsLength, char *aArgs[])
     VerifyOrExit(txLength >= OT_RADIO_FRAME_MIN_SIZE, error = kErrorInvalidArgs);
     mTxLen = txLength;
 
-    Output("sending %#x packet(s), length %#x\r\nstatus 0x%02x\r\n", static_cast<int>(mTxPackets),
-           static_cast<int>(mTxLen), error);
+    Output("sending %#x packet(s), length %#x\r\n", static_cast<int>(mTxPackets), static_cast<int>(mTxLen));
     TransmitPacket();
 
 exit:
-    AppendErrorResult(error);
     return error;
 }
 
@@ -501,10 +486,9 @@ Error Diags::ProcessStart(uint8_t aArgsLength, char *aArgs[])
     SuccessOrExit(error = Get<Radio>().SetTransmitPower(mTxPower));
     otPlatDiagModeSet(true);
     mStats.Clear();
-    Output("start diagnostics mode\r\nstatus 0x%02x\r\n", error);
+    Output("start diagnostics mode\r\n");
 
 exit:
-    AppendErrorResult(error);
     return error;
 }
 
@@ -512,8 +496,6 @@ Error Diags::ProcessStats(uint8_t aArgsLength, char *aArgs[])
 {
     Error error = kErrorNone;
 
-    VerifyOrExit(otPlatDiagModeGet(), error = kErrorInvalidState);
-
     if ((aArgsLength == 1) && StringMatch(aArgs[0], "clear"))
     {
         mStats.Clear();
@@ -531,7 +513,6 @@ Error Diags::ProcessStats(uint8_t aArgsLength, char *aArgs[])
     }
 
 exit:
-    AppendErrorResult(error);
     return error;
 }
 
@@ -540,10 +521,6 @@ Error Diags::ProcessStop(uint8_t aArgsLength, char *aArgs[])
     OT_UNUSED_VARIABLE(aArgsLength);
     OT_UNUSED_VARIABLE(aArgs);
 
-    Error error = kErrorNone;
-
-    VerifyOrExit(otPlatDiagModeGet(), error = kErrorInvalidState);
-
     otPlatAlarmMilliStop(&GetInstance());
     otPlatDiagModeSet(false);
     Get<Radio>().SetPromiscuous(false);
@@ -552,14 +529,12 @@ Error Diags::ProcessStop(uint8_t aArgsLength, char *aArgs[])
     Output("received packets: %d\r\nsent packets: %d\r\n"
            "first received packet: rssi=%d, lqi=%d\r\n"
            "last received packet: rssi=%d, lqi=%d\r\n"
-           "\nstop diagnostics mode\r\nstatus 0x%02x\r\n",
+           "\nstop diagnostics mode\r\n",
            static_cast<int>(mStats.mReceivedPackets), static_cast<int>(mStats.mSentPackets),
            static_cast<int>(mStats.mFirstRssi), static_cast<int>(mStats.mFirstLqi), static_cast<int>(mStats.mLastRssi),
-           static_cast<int>(mStats.mLastLqi), error);
+           static_cast<int>(mStats.mLastLqi));
 
-exit:
-    AppendErrorResult(error);
-    return error;
+    return kErrorNone;
 }
 
 void Diags::TransmitPacket(void)
@@ -635,13 +610,12 @@ Error Diags::ProcessRadio(uint8_t aArgsLength, char *aArgs[])
 {
     Error error = kErrorInvalidArgs;
 
-    VerifyOrExit(otPlatDiagModeGet(), error = kErrorInvalidState);
     VerifyOrExit(aArgsLength > 0, error = kErrorInvalidArgs);
 
     if (StringMatch(aArgs[0], "sleep"))
     {
         SuccessOrExit(error = Get<Radio>().Sleep());
-        Output("set radio from receive to sleep \r\nstatus 0x%02x\r\n", error);
+        Output("set radio from receive to sleep \r\n");
     }
     else if (StringMatch(aArgs[0], "receive"))
     {
@@ -653,7 +627,7 @@ Error Diags::ProcessRadio(uint8_t aArgsLength, char *aArgs[])
         if (aArgsLength == 0)
         {
             SuccessOrExit(error = RadioReceive());
-            Output("set radio from sleep to receive on channel %d\r\nstatus 0x%02x\r\n", mChannel, error);
+            Output("set radio from sleep to receive on channel %d\r\n", mChannel);
             ExitNow();
         }
 
@@ -723,7 +697,6 @@ Error Diags::ProcessRadio(uint8_t aArgsLength, char *aArgs[])
     }
 
 exit:
-    AppendErrorResult(error);
     return error;
 }
 
@@ -840,7 +813,6 @@ Error Diags::ProcessContinuousWave(uint8_t aArgsLength, char *aArgs[])
 {
     Error error = kErrorInvalidArgs;
 
-    VerifyOrExit(otPlatDiagModeGet(), error = kErrorInvalidState);
     VerifyOrExit(aArgsLength > 0, error = kErrorInvalidArgs);
 
     if (StringMatch(aArgs[0], "start"))
@@ -853,7 +825,6 @@ Error Diags::ProcessContinuousWave(uint8_t aArgsLength, char *aArgs[])
     }
 
 exit:
-    AppendErrorResult(error);
     return error;
 }
 
@@ -861,7 +832,6 @@ Error Diags::ProcessStream(uint8_t aArgsLength, char *aArgs[])
 {
     Error error = kErrorInvalidArgs;
 
-    VerifyOrExit(otPlatDiagModeGet(), error = kErrorInvalidState);
     VerifyOrExit(aArgsLength > 0, error = kErrorInvalidArgs);
 
     if (StringMatch(aArgs[0], "start"))
@@ -874,7 +844,6 @@ Error Diags::ProcessStream(uint8_t aArgsLength, char *aArgs[])
     }
 
 exit:
-    AppendErrorResult(error);
     return error;
 }
 
@@ -892,8 +861,6 @@ Error Diags::ProcessPowerSettings(uint8_t aArgsLength, char *aArgs[])
     uint8_t       channel;
     PowerSettings powerSettings;
 
-    VerifyOrExit(otPlatDiagModeGet(), error = kErrorInvalidState);
-
     if (aArgsLength == 0)
     {
         bool          isPrePowerSettingsValid = false;
@@ -936,7 +903,6 @@ Error Diags::ProcessPowerSettings(uint8_t aArgsLength, char *aArgs[])
     }
 
 exit:
-    AppendErrorResult(error);
     return error;
 }
 
@@ -951,8 +917,6 @@ Error Diags::ProcessRawPowerSetting(uint8_t aArgsLength, char *aArgs[])
     Error           error = kErrorInvalidArgs;
     RawPowerSetting setting;
 
-    VerifyOrExit(otPlatDiagModeGet(), error = kErrorInvalidState);
-
     if (aArgsLength == 0)
     {
         SuccessOrExit(error = GetRawPowerSetting(setting));
@@ -974,7 +938,6 @@ Error Diags::ProcessRawPowerSetting(uint8_t aArgsLength, char *aArgs[])
     }
 
 exit:
-    AppendErrorResult(error);
     return error;
 }
 
@@ -1024,7 +987,6 @@ Error Diags::ProcessGpio(uint8_t aArgsLength, char *aArgs[])
     }
 
 exit:
-    AppendErrorResult(error);
     return error;
 }
 
@@ -1112,6 +1074,12 @@ Error Diags::ProcessCmd(uint8_t aArgsLength, char *aArgs[])
         ExitNow();
     }
 
+    if (!otPlatDiagModeGet() && !StringMatch(aArgs[0], "start"))
+    {
+        Output("diagnostics mode is disabled\r\n");
+        ExitNow(error = kErrorInvalidState);
+    }
+
     for (const Command &command : sCommands)
     {
         if (StringMatch(aArgs[0], command.mName))
@@ -1131,6 +1099,8 @@ exit:
         Output("diag feature '%s' is not supported\r\n", aArgs[0]);
     }
 
+    AppendErrorResult(error);
+
     return error;
 }
 
diff --git a/tests/scripts/expect/cli-diags.exp b/tests/scripts/expect/cli-diags.exp
index 116412f8c..f235e2612 100755
--- a/tests/scripts/expect/cli-diags.exp
+++ b/tests/scripts/expect/cli-diags.exp
@@ -36,12 +36,10 @@ spawn_node 2
 switch_node 1
 send "diag start\n"
 expect "start diagnostics mode"
-expect "status 0x00"
 expect_line "Done"
 
 send "diag channel 11\n"
 expect "set channel to 11"
-expect "status 0x00"
 expect_line "Done"
 
 send "diag stats clear\n"
@@ -52,12 +50,10 @@ switch_node 2
 
 send "diag start\n"
 expect "start diagnostics mode"
-expect "status 0x00"
 expect_line "Done"
 
 send "diag channel 11\n"
 expect "set channel to 11"
-expect "status 0x00"
 expect_line "Done"
 
 send "diag stats clear\n"
@@ -66,7 +62,6 @@ expect_line "Done"
 
 send "diag send 10 100\n"
 expect "sending 0xa packet(s), length 0x64"
-expect "status 0x00"
 expect_line "Done"
 
 sleep 2
@@ -95,12 +90,10 @@ switch_node 2
 
 send "diag repeat 20 100\n"
 expect "sending packets of length 0x64 at the delay of 0x14 ms"
-expect "status 0x00"
 expect_line "Done"
 sleep 1
 send "diag repeat stop\n"
 expect "repeated packet transmission is stopped"
-expect "status 0x00"
 expect_line "Done"
 
 switch_node 1
@@ -123,7 +116,6 @@ spawn_node 1
 
 send "diag start\n"
 expect "start diagnostics mode"
-expect "status 0x00"
 expect_line "Done"
 
 send_user "input too short test\n"
@@ -178,17 +170,14 @@ expect "Done"
 
 send "diag channel 11\n"
 expect "set channel to 11"
-expect "status 0x00"
 expect_line "Done"
 
 send "diag power 10\n"
 expect "set tx power to 10 dBm"
-expect "status 0x00"
 expect_line "Done"
 
 send "diag radio sleep\n"
 expect "set radio from receive to sleep"
-expect "status 0x00"
 expect_line "Done"
 
 send "diag radio state\n"
@@ -197,7 +186,6 @@ expect_line "Done"
 
 send "diag radio receive\n"
 expect "set radio from sleep to receive on channel 11"
-expect "status 0x00"
 expect_line "Done"
 
 send "diag radio state\n"
diff --git a/tests/scripts/expect/posix-diag-rcp.exp b/tests/scripts/expect/posix-diag-rcp.exp
index e585d60b4..c9fa1725b 100755
--- a/tests/scripts/expect/posix-diag-rcp.exp
+++ b/tests/scripts/expect/posix-diag-rcp.exp
@@ -33,10 +33,11 @@ spawn_node 1
 
 send "diag rcp\n"
 expect "diagnostics mode is disabled"
-expect_line "Done"
+expect_line "failed"
+expect_line "status 0xd"
+expect_line "Error 13: InvalidState"
 send "diag start\n"
 expect "start diagnostics mode"
-expect "status 0x00"
 expect_line "Done"
 send "diag rcp\n"
 expect "diagnostics mode is enabled"
diff --git a/tests/scripts/expect/posix-power-calibration.exp b/tests/scripts/expect/posix-power-calibration.exp
index a8f15fb29..ac56d16bc 100755
--- a/tests/scripts/expect/posix-power-calibration.exp
+++ b/tests/scripts/expect/posix-power-calibration.exp
@@ -33,7 +33,6 @@ spawn_node 1
 
 send "diag start\n"
 expect "start diagnostics mode"
-expect "status 0x00"
 expect_line "Done"
 
 send "diag powersettings 11\n"
@@ -54,7 +53,6 @@ expect_line "Done"
 
 send "diag start\n"
 expect "start diagnostics mode"
-expect "status 0x00"
 expect_line "Done"
 
 send "diag powersettings 11\n"
diff --git a/tests/scripts/thread-cert/test_diag.py b/tests/scripts/thread-cert/test_diag.py
index db633f544..d5931b5f8 100755
--- a/tests/scripts/thread-cert/test_diag.py
+++ b/tests/scripts/thread-cert/test_diag.py
@@ -48,9 +48,9 @@ class TestDiag(thread_cert.TestCase):
             ('diag invalid test\n', 'diag feature \'invalid\' is not supported'),
             ('diag', 'diagnostics mode is enabled\r\n'),
             ('diag channel 10', 'failed\r\nstatus 0x7\r\n'),
-            ('diag channel 11', 'set channel to 11\r\nstatus 0x00\r\n'),
+            ('diag channel 11', 'set channel to 11\r\n'),
             ('diag channel', 'channel: 11\r\n'),
-            ('diag power -10', 'set tx power to -10 dBm\r\nstatus 0x00\r\n'),
+            ('diag power -10', 'set tx power to -10 dBm\r\n'),
             ('diag power', 'tx power: -10 dBm\r\n'),
             (
                 'diag stats',
@@ -60,26 +60,26 @@ class TestDiag(thread_cert.TestCase):
             ),
             (
                 'diag send 20 100',
-                r'sending 0x14 packet\(s\), length 0x64\r\nstatus 0x00\r\n',
+                r'sending 0x14 packet\(s\), length 0x64\r\n',
             ),
             (
                 '  diag \t send    \t 20\t100',
-                r'sending 0x14 packet\(s\), length 0x64\r\nstatus 0x00\r\n',
+                r'sending 0x14 packet\(s\), length 0x64\r\n',
             ),
             (
                 'diag repeat 100 100',
-                'sending packets of length 0x64 at the delay of 0x64 ms\r\nstatus 0x00\r\n',
+                'sending packets of length 0x64 at the delay of 0x64 ms\r\n',
             ),
             (
                 'diag repeat stop',
-                'repeated packet transmission is stopped\r\nstatus 0x00\r\n',
+                'repeated packet transmission is stopped\r\n',
             ),
             (
                 'diag stop',
                 r'received packets: 0\r\nsent packets: ([1-9]\d*)\r\n'
                 'first received packet: rssi=0, lqi=0\r\n'
                 'last received packet: rssi=0, lqi=0\r\n\n'
-                r'stop diagnostics mode\r\nstatus 0x00\r\n',
+                r'stop diagnostics mode\r\n',
             ),
             ('diag', 'diagnostics mode is disabled\r\n'),
             (