diff --git a/.clang-tidy b/.clang-tidy
index 50c4d9633..61af657f6 100644
--- a/.clang-tidy
+++ b/.clang-tidy
@@ -2,6 +2,7 @@
 Checks: >
   -*,
   bugprone-argument-comment,
+  bugprone-too-small-loop-variable,
   google-explicit-constructor,
   google-readability-casting,
   misc-unused-using-decls,
diff --git a/examples/platforms/simulation/flash.c b/examples/platforms/simulation/flash.c
index ce07f3a70..59461e0e9 100644
--- a/examples/platforms/simulation/flash.c
+++ b/examples/platforms/simulation/flash.c
@@ -84,7 +84,7 @@ void otPlatFlashInit(otInstance *aInstance)
 
     if (create)
     {
-        for (uint8_t index = 0; index < SWAP_NUM; index++)
+        for (uint8_t index = 0; index < (uint8_t)SWAP_NUM; index++)
         {
             otPlatFlashErase(aInstance, index);
         }
diff --git a/examples/platforms/simulation/radio.c b/examples/platforms/simulation/radio.c
index 9fe37b66c..6ba2a5dcf 100644
--- a/examples/platforms/simulation/radio.c
+++ b/examples/platforms/simulation/radio.c
@@ -236,7 +236,7 @@ otError ProcessNodeIdFilter(void *aContext, uint8_t aArgsLength, char *aArgs[])
             break;
         }
 
-        for (uint16_t nodeId = 0; nodeId <= MAX_NETWORK_SIZE; nodeId++)
+        for (uint16_t nodeId = 0; nodeId <= (uint16_t)MAX_NETWORK_SIZE; nodeId++)
         {
             if (FilterContainsId(nodeId))
             {
diff --git a/src/cli/cli.cpp b/src/cli/cli.cpp
index fcfee7b9d..b814d092b 100644
--- a/src/cli/cli.cpp
+++ b/src/cli/cli.cpp
@@ -5256,7 +5256,7 @@ void Interpreter::HandleMeshDiagDiscoverDone(otError aError, otMeshDiagRouterInf
         {
             OutputFormat(kIndentSize, "%u-links:{ ", linkQuality);
 
-            for (uint8_t id = 0; id < OT_ARRAY_LENGTH(aRouterInfo->mLinkQualities); id++)
+            for (uint8_t id = 0; id < static_cast<uint8_t>(OT_ARRAY_LENGTH(aRouterInfo->mLinkQualities)); id++)
             {
                 if (aRouterInfo->mLinkQualities[id] == linkQuality)
                 {
diff --git a/src/cli/cli_dns.cpp b/src/cli/cli_dns.cpp
index 8d7e0a414..c532a0f6f 100644
--- a/src/cli/cli_dns.cpp
+++ b/src/cli/cli_dns.cpp
@@ -496,7 +496,7 @@ otError Dns::ParseDnsServiceMode(const Arg &aArg, otDnsServiceMode &aMode) const
         ExitNow();
     }
 
-    for (uint8_t index = 0; index < OT_ARRAY_LENGTH(kServiceModeStrings); index++)
+    for (size_t index = 0; index < OT_ARRAY_LENGTH(kServiceModeStrings); index++)
     {
         if (aArg == kServiceModeStrings[index])
         {
diff --git a/src/cli/cli_mac_filter.cpp b/src/cli/cli_mac_filter.cpp
index 6525a20aa..7201c0423 100644
--- a/src/cli/cli_mac_filter.cpp
+++ b/src/cli/cli_mac_filter.cpp
@@ -173,7 +173,7 @@ template <> otError MacFilter::Process<Cmd("addr")>(Arg aArgs[])
             "denylist",  // (2) OT_MAC_FILTER_ADDRESS_MODE_DENYLIST
         };
 
-        for (uint8_t index = 0; index < OT_ARRAY_LENGTH(kModeCommands); index++)
+        for (size_t index = 0; index < OT_ARRAY_LENGTH(kModeCommands); index++)
         {
             if (aArgs[0] == kModeCommands[index])
             {
diff --git a/src/core/meshcop/meshcop.cpp b/src/core/meshcop/meshcop.cpp
index 6fb17b020..9dd65663c 100644
--- a/src/core/meshcop/meshcop.cpp
+++ b/src/core/meshcop/meshcop.cpp
@@ -64,7 +64,7 @@ bool JoinerPskd::operator==(const JoinerPskd &aOther) const
 {
     bool isEqual = true;
 
-    for (uint8_t i = 0; i < sizeof(m8); i++)
+    for (size_t i = 0; i < sizeof(m8); i++)
     {
         if (m8[i] != aOther.m8[i])
         {
diff --git a/src/core/thread/network_diagnostic.cpp b/src/core/thread/network_diagnostic.cpp
index be009f396..97926091d 100644
--- a/src/core/thread/network_diagnostic.cpp
+++ b/src/core/thread/network_diagnostic.cpp
@@ -340,7 +340,7 @@ Error Server::AppendDiagTlv(uint8_t aTlvType, Message &aMessage)
 
         tlv.Init();
 
-        for (uint8_t page = 0; page < sizeof(Radio::kSupportedChannelPages) * CHAR_BIT; page++)
+        for (uint8_t page = 0; page < static_cast<uint8_t>(sizeof(Radio::kSupportedChannelPages) * CHAR_BIT); page++)
         {
             if (Radio::kSupportedChannelPages & (1 << page))
             {
diff --git a/tests/unit/test_cmd_line_parser.cpp b/tests/unit/test_cmd_line_parser.cpp
index 7f832cf11..cc2a93595 100644
--- a/tests/unit/test_cmd_line_parser.cpp
+++ b/tests/unit/test_cmd_line_parser.cpp
@@ -309,7 +309,7 @@ void TestParsingHexStrings(void)
 
     for (uint8_t testIter = 0; testIter <= 1; testIter++)
     {
-        for (uint8_t segmentLen = 1; segmentLen <= sizeof(buffer); segmentLen++)
+        for (size_t segmentLen = 1; segmentLen <= sizeof(buffer); segmentLen++)
         {
             if (testIter == 0)
             {
@@ -324,7 +324,7 @@ void TestParsingHexStrings(void)
 
             len = segmentLen;
 
-            printf("\"%s\" segLen:%d -> ", string, segmentLen);
+            printf("\"%s\" segLen:%zu -> ", string, segmentLen);
 
             while (true)
             {
diff --git a/tests/unit/test_hkdf_sha256.cpp b/tests/unit/test_hkdf_sha256.cpp
index a50ac8488..019db5690 100644
--- a/tests/unit/test_hkdf_sha256.cpp
+++ b/tests/unit/test_hkdf_sha256.cpp
@@ -150,7 +150,7 @@ void TestHkdfSha256(void)
 
         VerifyOrQuit(memcmp(outKey, test->mOutKey, test->mOutKeyLength) == 0, "HKDF-SHA-256 failed");
 
-        for (uint16_t i = test->mOutKeyLength + 1; i < sizeof(outKey); i++)
+        for (size_t i = test->mOutKeyLength + 1; i < sizeof(outKey); i++)
         {
             VerifyOrQuit(outKey[i] == kFillByte, "HKDF-SHA-256 wrote beyond output key length");
         }
diff --git a/tests/unit/test_ip_address.cpp b/tests/unit/test_ip_address.cpp
index 153a2c13a..a3b71cf42 100644
--- a/tests/unit/test_ip_address.cpp
+++ b/tests/unit/test_ip_address.cpp
@@ -366,7 +366,7 @@ bool CheckInterfaceId(const ot::Ip6::Address &aAddress1, const ot::Ip6::Address
 
     bool matches = true;
 
-    for (uint8_t bit = aPrefixLength; bit < sizeof(ot::Ip6::Address) * CHAR_BIT; bit++)
+    for (size_t bit = aPrefixLength; bit < sizeof(ot::Ip6::Address) * CHAR_BIT; bit++)
     {
         uint8_t index = bit / CHAR_BIT;
         uint8_t mask  = (0x80 >> (bit % CHAR_BIT));
@@ -403,14 +403,14 @@ void TestIp6AddressSetPrefix(void)
         memcpy(address.mFields.m8, prefix, sizeof(address));
         printf("Prefix is %s\n", address.ToString().AsCString());
 
-        for (uint8_t prefixLength = 0; prefixLength <= sizeof(ot::Ip6::Address) * CHAR_BIT; prefixLength++)
+        for (size_t prefixLength = 0; prefixLength <= sizeof(ot::Ip6::Address) * CHAR_BIT; prefixLength++)
         {
             ip6Prefix.Clear();
             ip6Prefix.Set(prefix, prefixLength);
 
             address = allZeroAddress;
             address.SetPrefix(ip6Prefix);
-            printf("   prefix-len:%-3d --> %s\n", prefixLength, address.ToString().AsCString());
+            printf("   prefix-len:%-3zu --> %s\n", prefixLength, address.ToString().AsCString());
             VerifyOrQuit(CheckPrefix(address, prefix, prefixLength), "Prefix does not match after SetPrefix()");
             VerifyOrQuit(CheckInterfaceId(address, allZeroAddress, prefixLength),
                          "SetPrefix changed bits beyond the prefix length");
diff --git a/tests/unit/test_mac_frame.cpp b/tests/unit/test_mac_frame.cpp
index 7966b70e9..b92003f8c 100644
--- a/tests/unit/test_mac_frame.cpp
+++ b/tests/unit/test_mac_frame.cpp
@@ -442,7 +442,7 @@ void TestMacChannelMask(void)
     VerifyChannelMaskContent(mask1, allChannels, sizeof(allChannels));
 
     // Test ChannelMask::RemoveChannel()
-    for (uint8_t index = 0; index < sizeof(allChannels) - 1; index++)
+    for (size_t index = 0; index < sizeof(allChannels) - 1; index++)
     {
         mask1.RemoveChannel(allChannels[index]);
         VerifyChannelMaskContent(mask1, &allChannels[index + 1], sizeof(allChannels) - 1 - index);
diff --git a/tests/unit/test_nat64.cpp b/tests/unit/test_nat64.cpp
index 66e5fbeb1..d699d83f8 100644
--- a/tests/unit/test_nat64.cpp
+++ b/tests/unit/test_nat64.cpp
@@ -50,7 +50,7 @@ void DumpMessageInHex(const char *prefix, const uint8_t *aBuf, size_t aBufLen)
 {
     // This function dumps all packets the output of this function can be imported to packet analyser for debugging.
     printf("%s", prefix);
-    for (uint16_t i = 0; i < aBufLen; i++)
+    for (size_t i = 0; i < aBufLen; i++)
     {
         printf("%02x", aBuf[i]);
     }
@@ -71,7 +71,7 @@ bool CheckMessage(const Message &aMessage, const uint8_t *aExpectedMessage, size
     if (!success)
     {
         printf("Expected Message\n");
-        for (uint16_t i = 0; i < aExpectedMessageLen; i++)
+        for (size_t i = 0; i < aExpectedMessageLen; i++)
         {
             printf("%02x%c", aExpectedMessage[i], " \n"[(i & 0xf) == 0xf]);
         }
diff --git a/tests/unit/test_toolchain.cpp b/tests/unit/test_toolchain.cpp
index 643b502fe..def163462 100644
--- a/tests/unit/test_toolchain.cpp
+++ b/tests/unit/test_toolchain.cpp
@@ -132,7 +132,7 @@ void test_packed_alignment(void)
     packedStruct.mByte   = 0xfe;
     packedStruct.mUint16 = 0xabcd;
 
-    for (uint16_t start = 0; start < sizeof(PackedStruct); start++)
+    for (size_t start = 0; start < sizeof(PackedStruct); start++)
     {
         uint8_t *ptr = &buffer[start];
 
@@ -140,14 +140,14 @@ void test_packed_alignment(void)
 
         *reinterpret_cast<PackedStruct *>(ptr) = packedStruct;
 
-        for (uint16_t i = 0; i < start; i++)
+        for (size_t i = 0; i < start; i++)
         {
             VerifyOrQuit(buffer[i] == 0, "OT_TOOL_PACKED alignment failed - pre-size write");
         }
 
         VerifyOrQuit(memcmp(ptr, packedStructBytes, sizeof(PackedStruct)) == 0, "OT_TOOL_PACKED alignment failed");
 
-        for (uint16_t i = start + sizeof(packedStruct); i < sizeof(buffer); i++)
+        for (size_t i = start + sizeof(packedStruct); i < sizeof(buffer); i++)
         {
             VerifyOrQuit(buffer[i] == 0, "OT_TOOL_PACKED alignment failed - post-size write");
         }