diff --git a/include/openthread/backbone_router_ftd.h b/include/openthread/backbone_router_ftd.h
index 64fc71615..e27551959 100644
--- a/include/openthread/backbone_router_ftd.h
+++ b/include/openthread/backbone_router_ftd.h
@@ -328,7 +328,7 @@ typedef enum
  *
  * @param[in] aContext  The user context pointer.
  * @param[in] aEvent    The ND Proxy event.
- * @param[in] aDua      The Domain Unicast Address of the ND Proxy, or `nullptr` if @p aEvent is
+ * @param[in] aDua      The Domain Unicast Address of the ND Proxy, or NULL if @p aEvent is
  *                      `OT_BACKBONE_ROUTER_NDPROXY_CLEARED`.
  */
 typedef void (*otBackboneRouterNdProxyCallback)(void                        *aContext,
@@ -385,7 +385,7 @@ typedef enum
  *
  * @param[in] aContext       The user context pointer.
  * @param[in] aEvent         The Domain Prefix event.
- * @param[in] aDomainPrefix  The new Domain Prefix if added or changed, nullptr otherwise.
+ * @param[in] aDomainPrefix  The new Domain Prefix if added or changed, NULL otherwise.
  */
 typedef void (*otBackboneRouterDomainPrefixCallback)(void                             *aContext,
                                                      otBackboneRouterDomainPrefixEvent aEvent,
diff --git a/include/openthread/instance.h b/include/openthread/instance.h
index a8cd3b5fd..5e3c69303 100644
--- a/include/openthread/instance.h
+++ b/include/openthread/instance.h
@@ -52,7 +52,7 @@ extern "C" {
  *
  * @note This number versions both OpenThread platform and user APIs.
  */
-#define OPENTHREAD_API_VERSION (499)
+#define OPENTHREAD_API_VERSION (500)
 
 /**
  * @addtogroup api-instance
diff --git a/include/openthread/link.h b/include/openthread/link.h
index ccdc2c7aa..5d41d1de1 100644
--- a/include/openthread/link.h
+++ b/include/openthread/link.h
@@ -1102,7 +1102,7 @@ otError otLinkSetRegion(otInstance *aInstance, uint16_t aRegionCode);
  * @param[out] aRegionCode  The radio region code. The `aRegionCode >> 8` is first ascii char
  *                          and the `aRegionCode & 0xff` is the second ascii char.
  *
- * @retval  OT_ERROR_INVALID_ARGS     @p aRegionCode is nullptr.
+ * @retval  OT_ERROR_INVALID_ARGS     @p aRegionCode is NULL.
  * @retval  OT_ERROR_FAILED           Other platform specific errors.
  * @retval  OT_ERROR_NONE             Successfully got region code.
  * @retval  OT_ERROR_NOT_IMPLEMENTED  The feature is not implemented.
diff --git a/include/openthread/nat64.h b/include/openthread/nat64.h
index 1ac93701a..c6c6ace4a 100644
--- a/include/openthread/nat64.h
+++ b/include/openthread/nat64.h
@@ -446,7 +446,7 @@ void otIp4ToIp4MappedIp6Address(const otIp4Address *aIp4Address, otIp6Address *a
  * truncated but the outputted string is always null-terminated.
  *
  * @param[in]  aAddress  A pointer to an IPv4 address (MUST NOT be NULL).
- * @param[out] aBuffer   A pointer to a char array to output the string (MUST NOT be `nullptr`).
+ * @param[out] aBuffer   A pointer to a char array to output the string (MUST NOT be NULL).
  * @param[in]  aSize     The size of @p aBuffer (in bytes).
  */
 void otIp4AddressToString(const otIp4Address *aAddress, char *aBuffer, uint16_t aSize);
@@ -474,7 +474,7 @@ otError otIp4CidrFromString(const char *aString, otIp4Cidr *aCidr);
  * truncated but the outputted string is always null-terminated.
  *
  * @param[in]  aCidr     A pointer to an IPv4 CIDR (MUST NOT be NULL).
- * @param[out] aBuffer   A pointer to a char array to output the string (MUST NOT be `nullptr`).
+ * @param[out] aBuffer   A pointer to a char array to output the string (MUST NOT be NULL).
  * @param[in]  aSize     The size of @p aBuffer (in bytes).
  */
 void otIp4CidrToString(const otIp4Cidr *aCidr, char *aBuffer, uint16_t aSize);
diff --git a/include/openthread/platform/dns.h b/include/openthread/platform/dns.h
index 326fded12..e15e843aa 100644
--- a/include/openthread/platform/dns.h
+++ b/include/openthread/platform/dns.h
@@ -87,11 +87,11 @@ void otPlatDnsCancelUpstreamQuery(otInstance *aInstance, otPlatDnsUpstreamQuery
  * The transaction will be released, so the platform must not call on the same transaction twice. This function passes
  * the ownership of `aResponse` to OpenThread stack.
  *
- * Platform can pass a nullptr to close a transaction without a response.
+ * Platform can pass NULL to close a transaction without a response.
  *
  * @param[in] aInstance  The OpenThread instance structure.
  * @param[in] aTxn       A pointer to the opaque DNS query transaction object.
- * @param[in] aResponse  A message buffer of the DNS response payload or `nullptr` to close a transaction without a
+ * @param[in] aResponse  A message buffer of the DNS response payload or NULL to close a transaction without a
  *                       response.
  */
 extern void otPlatDnsUpstreamQueryDone(otInstance *aInstance, otPlatDnsUpstreamQuery *aTxn, otMessage *aResponse);
diff --git a/include/openthread/platform/multipan.h b/include/openthread/platform/multipan.h
index adece8af6..897dcb297 100644
--- a/include/openthread/platform/multipan.h
+++ b/include/openthread/platform/multipan.h
@@ -115,7 +115,7 @@ extern void otPlatMultipanSwitchoverDone(otInstance *aInstance, bool aSuccess);
  *
  * @param[in] aIid  The IID of the interface.
  *
- * @retval  Instance pointer if aIid is has an instance assigned, nullptr otherwise.
+ * @retval  Instance pointer if aIid is has an instance assigned, NULL otherwise.
  */
 otInstance *otPlatMultipanIidToInstance(uint8_t aIid);
 
diff --git a/include/openthread/platform/radio.h b/include/openthread/platform/radio.h
index 8e45fd2eb..b49be9cfd 100644
--- a/include/openthread/platform/radio.h
+++ b/include/openthread/platform/radio.h
@@ -1193,7 +1193,7 @@ otError otPlatRadioEnableCsl(otInstance         *aInstance,
 /**
  * Reset CSL receiver in the platform.
  *
- * @note Defaults to `otPlatRadioEnableCsl(aInstance,0, Mac::kShortAddrInvalid, nullptr);`
+ * @note Defaults to `otPlatRadioEnableCsl(aInstance,0, Mac::kShortAddrInvalid, NULL);`
  *
  * @param[in]  aInstance     The OpenThread instance structure.
  *
@@ -1298,7 +1298,7 @@ otError otPlatRadioSetRegion(otInstance *aInstance, uint16_t aRegionCode);
  * @param[in]  aInstance    The OpenThread instance structure.
  * @param[out] aRegionCode  The radio region.
  *
- * @retval  OT_ERROR_INVALID_ARGS     @p aRegionCode is nullptr.
+ * @retval  OT_ERROR_INVALID_ARGS     @p aRegionCode is NULL.
  * @retval  OT_ERROR_FAILED           Other platform specific errors.
  * @retval  OT_ERROR_NONE             Successfully got region code.
  * @retval  OT_ERROR_NOT_IMPLEMENTED  The feature is not implemented.