diff --git a/include/openthread/coap.h b/include/openthread/coap.h
index dc2a031ac..f7733d946 100644
--- a/include/openthread/coap.h
+++ b/include/openthread/coap.h
@@ -850,11 +850,8 @@ otError otCoapStop(otInstance *aInstance);
  * @param[in]  aInstance  A pointer to an OpenThread instance.
  * @param[in]  aResource  A pointer to the resource.
  *
- * @retval OT_ERROR_NONE     Successfully added @p aResource.
- * @retval OT_ERROR_ALREADY  The @p aResource was already added.
- *
  */
-otError otCoapAddResource(otInstance *aInstance, otCoapResource *aResource);
+void otCoapAddResource(otInstance *aInstance, otCoapResource *aResource);
 
 /**
  * This function removes a resource from the CoAP server.
diff --git a/include/openthread/coap_secure.h b/include/openthread/coap_secure.h
index e939fe58f..11caec54d 100644
--- a/include/openthread/coap_secure.h
+++ b/include/openthread/coap_secure.h
@@ -257,11 +257,8 @@ otError otCoapSecureSendRequest(otInstance *          aInstance,
  * @param[in]  aInstance  A pointer to an OpenThread instance.
  * @param[in]  aResource  A pointer to the resource.
  *
- * @retval OT_ERROR_NONE     Successfully added @p aResource.
- * @retval OT_ERROR_ALREADY  The @p aResource was already added.
- *
  */
-otError otCoapSecureAddResource(otInstance *aInstance, otCoapResource *aResource);
+void otCoapSecureAddResource(otInstance *aInstance, otCoapResource *aResource);
 
 /**
  * This function removes a resource from the CoAP Secure server.
diff --git a/src/cli/cli_coap.cpp b/src/cli/cli_coap.cpp
index 628ce217c..8812eef8d 100644
--- a/src/cli/cli_coap.cpp
+++ b/src/cli/cli_coap.cpp
@@ -193,7 +193,7 @@ otError Coap::ProcessResource(uint8_t aArgsLength, char *aArgs[])
         mResource.mHandler = &Coap::HandleRequest;
 
         strncpy(mUriPath, aArgs[1], sizeof(mUriPath) - 1);
-        SuccessOrExit(error = otCoapAddResource(mInterpreter.mInstance, &mResource));
+        otCoapAddResource(mInterpreter.mInstance, &mResource);
     }
     else
     {
diff --git a/src/cli/cli_coap_secure.cpp b/src/cli/cli_coap_secure.cpp
index fa7c3e648..4a5fcc623 100644
--- a/src/cli/cli_coap_secure.cpp
+++ b/src/cli/cli_coap_secure.cpp
@@ -124,7 +124,7 @@ otError CoapSecure::ProcessResource(uint8_t aArgsLength, char *aArgs[])
         mResource.mHandler = &CoapSecure::HandleRequest;
 
         strncpy(mUriPath, aArgs[1], sizeof(mUriPath) - 1);
-        SuccessOrExit(error = otCoapSecureAddResource(mInterpreter.mInstance, &mResource));
+        otCoapSecureAddResource(mInterpreter.mInstance, &mResource);
     }
     else
     {
@@ -132,7 +132,7 @@ otError CoapSecure::ProcessResource(uint8_t aArgsLength, char *aArgs[])
     }
 
 exit:
-    return OT_ERROR_NONE;
+    return error;
 }
 
 otError CoapSecure::ProcessStart(uint8_t aArgsLength, char *aArgs[])
diff --git a/src/core/api/coap_api.cpp b/src/core/api/coap_api.cpp
index dc963596b..d4dcf86a7 100644
--- a/src/core/api/coap_api.cpp
+++ b/src/core/api/coap_api.cpp
@@ -249,11 +249,11 @@ otError otCoapStop(otInstance *aInstance)
     return instance.GetApplicationCoap().Stop();
 }
 
-otError otCoapAddResource(otInstance *aInstance, otCoapResource *aResource)
+void otCoapAddResource(otInstance *aInstance, otCoapResource *aResource)
 {
     Instance &instance = *static_cast<Instance *>(aInstance);
 
-    return instance.GetApplicationCoap().AddResource(*static_cast<Coap::Resource *>(aResource));
+    instance.GetApplicationCoap().AddResource(*static_cast<Coap::Resource *>(aResource));
 }
 
 void otCoapRemoveResource(otInstance *aInstance, otCoapResource *aResource)
diff --git a/src/core/api/coap_secure_api.cpp b/src/core/api/coap_secure_api.cpp
index 6fb973d4d..7139fa728 100644
--- a/src/core/api/coap_secure_api.cpp
+++ b/src/core/api/coap_secure_api.cpp
@@ -161,11 +161,11 @@ otError otCoapSecureSendRequest(otInstance *          aInstance,
     return instance.GetApplicationCoapSecure().SendMessage(*static_cast<Coap::Message *>(aMessage), aHandler, aContext);
 }
 
-otError otCoapSecureAddResource(otInstance *aInstance, otCoapResource *aResource)
+void otCoapSecureAddResource(otInstance *aInstance, otCoapResource *aResource)
 {
     Instance &instance = *static_cast<Instance *>(aInstance);
 
-    return instance.GetApplicationCoapSecure().AddResource(*static_cast<Coap::Resource *>(aResource));
+    instance.GetApplicationCoapSecure().AddResource(*static_cast<Coap::Resource *>(aResource));
 }
 
 void otCoapSecureRemoveResource(otInstance *aInstance, otCoapResource *aResource)
diff --git a/src/core/coap/coap.cpp b/src/core/coap/coap.cpp
index 530b4ad72..0c4c394bf 100644
--- a/src/core/coap/coap.cpp
+++ b/src/core/coap/coap.cpp
@@ -90,9 +90,9 @@ void CoapBase::ClearRequests(const Ip6::Address *aAddress)
     }
 }
 
-otError CoapBase::AddResource(Resource &aResource)
+void CoapBase::AddResource(Resource &aResource)
 {
-    return mResources.Add(aResource);
+    IgnoreError(mResources.Add(aResource));
 }
 
 void CoapBase::RemoveResource(Resource &aResource)
diff --git a/src/core/coap/coap.hpp b/src/core/coap/coap.hpp
index 10bdf27fa..f314f797e 100644
--- a/src/core/coap/coap.hpp
+++ b/src/core/coap/coap.hpp
@@ -307,11 +307,8 @@ public:
      *
      * @param[in]  aResource  A reference to the resource.
      *
-     * @retval OT_ERROR_NONE     Successfully added @p aResource.
-     * @retval OT_ERROR_ALREADY  The @p aResource was already added.
-     *
      */
-    otError AddResource(Resource &aResource);
+    void AddResource(Resource &aResource);
 
     /**
      * This method removes a resource from the CoAP server.
diff --git a/src/core/meshcop/border_agent.cpp b/src/core/meshcop/border_agent.cpp
index a92e2190d..ca3be6b70 100644
--- a/src/core/meshcop/border_agent.cpp
+++ b/src/core/meshcop/border_agent.cpp
@@ -676,18 +676,18 @@ otError BorderAgent::Start(void)
     SuccessOrExit(error = coaps.SetPsk(Get<KeyManager>().GetPskc().m8, OT_PSKC_MAX_SIZE));
     coaps.SetConnectedCallback(HandleConnected, this);
 
-    IgnoreError(coaps.AddResource(mActiveGet));
-    IgnoreError(coaps.AddResource(mActiveSet));
-    IgnoreError(coaps.AddResource(mPendingGet));
-    IgnoreError(coaps.AddResource(mPendingSet));
-    IgnoreError(coaps.AddResource(mCommissionerPetition));
-    IgnoreError(coaps.AddResource(mCommissionerKeepAlive));
-    IgnoreError(coaps.AddResource(mCommissionerSet));
-    IgnoreError(coaps.AddResource(mCommissionerGet));
-    IgnoreError(coaps.AddResource(mProxyTransmit));
-    IgnoreError(coaps.AddResource(mRelayTransmit));
+    coaps.AddResource(mActiveGet);
+    coaps.AddResource(mActiveSet);
+    coaps.AddResource(mPendingGet);
+    coaps.AddResource(mPendingSet);
+    coaps.AddResource(mCommissionerPetition);
+    coaps.AddResource(mCommissionerKeepAlive);
+    coaps.AddResource(mCommissionerSet);
+    coaps.AddResource(mCommissionerGet);
+    coaps.AddResource(mProxyTransmit);
+    coaps.AddResource(mRelayTransmit);
 
-    IgnoreError(Get<Coap::Coap>().AddResource(mRelayReceive));
+    Get<Coap::Coap>().AddResource(mRelayReceive);
 
     SetState(OT_BORDER_AGENT_STATE_STARTED);
 
diff --git a/src/core/meshcop/commissioner.cpp b/src/core/meshcop/commissioner.cpp
index 38f265174..b14c50437 100644
--- a/src/core/meshcop/commissioner.cpp
+++ b/src/core/meshcop/commissioner.cpp
@@ -114,9 +114,9 @@ void Commissioner::SignalJoinerEvent(otCommissionerJoinerEvent aEvent, const Mac
 
 void Commissioner::AddCoapResources(void)
 {
-    IgnoreError(Get<Coap::Coap>().AddResource(mRelayReceive));
-    IgnoreError(Get<Coap::Coap>().AddResource(mDatasetChanged));
-    IgnoreError(Get<Coap::CoapSecure>().AddResource(mJoinerFinalize));
+    Get<Coap::Coap>().AddResource(mRelayReceive);
+    Get<Coap::Coap>().AddResource(mDatasetChanged);
+    Get<Coap::CoapSecure>().AddResource(mJoinerFinalize);
 }
 
 void Commissioner::RemoveCoapResources(void)
diff --git a/src/core/meshcop/dataset_manager.cpp b/src/core/meshcop/dataset_manager.cpp
index 110038f5e..2efaa2a14 100644
--- a/src/core/meshcop/dataset_manager.cpp
+++ b/src/core/meshcop/dataset_manager.cpp
@@ -683,7 +683,7 @@ ActiveDataset::ActiveDataset(Instance &aInstance)
     , mResourceSet(OT_URI_PATH_ACTIVE_SET, &ActiveDataset::HandleSet, this)
 #endif
 {
-    IgnoreError(Get<Coap::Coap>().AddResource(mResourceGet));
+    Get<Coap::Coap>().AddResource(mResourceGet);
 }
 
 bool ActiveDataset::IsPartiallyComplete(void) const
@@ -732,7 +732,7 @@ PendingDataset::PendingDataset(Instance &aInstance)
     , mResourceSet(OT_URI_PATH_PENDING_SET, &PendingDataset::HandleSet, this)
 #endif
 {
-    IgnoreError(Get<Coap::Coap>().AddResource(mResourceGet));
+    Get<Coap::Coap>().AddResource(mResourceGet);
 }
 
 void PendingDataset::Clear(void)
diff --git a/src/core/meshcop/dataset_manager_ftd.cpp b/src/core/meshcop/dataset_manager_ftd.cpp
index 25da998d1..5ad882412 100644
--- a/src/core/meshcop/dataset_manager_ftd.cpp
+++ b/src/core/meshcop/dataset_manager_ftd.cpp
@@ -461,7 +461,7 @@ exit:
 void ActiveDataset::StartLeader(void)
 {
     IgnoreError(GenerateLocal());
-    IgnoreError(Get<Coap::Coap>().AddResource(mResourceSet));
+    Get<Coap::Coap>().AddResource(mResourceSet);
 }
 
 void ActiveDataset::StopLeader(void)
@@ -487,7 +487,7 @@ exit:
 void PendingDataset::StartLeader(void)
 {
     StartDelayTimer();
-    IgnoreError(Get<Coap::Coap>().AddResource(mResourceSet));
+    Get<Coap::Coap>().AddResource(mResourceSet);
 }
 
 void PendingDataset::StopLeader(void)
diff --git a/src/core/meshcop/energy_scan_client.cpp b/src/core/meshcop/energy_scan_client.cpp
index 0cee3e573..4f4f7d234 100644
--- a/src/core/meshcop/energy_scan_client.cpp
+++ b/src/core/meshcop/energy_scan_client.cpp
@@ -51,11 +51,11 @@ namespace ot {
 
 EnergyScanClient::EnergyScanClient(Instance &aInstance)
     : InstanceLocator(aInstance)
+    , mCallback(NULL)
+    , mContext(NULL)
     , mEnergyScan(OT_URI_PATH_ENERGY_REPORT, &EnergyScanClient::HandleReport, this)
 {
-    mContext  = NULL;
-    mCallback = NULL;
-    IgnoreError(Get<Coap::Coap>().AddResource(mEnergyScan));
+    Get<Coap::Coap>().AddResource(mEnergyScan);
 }
 
 otError EnergyScanClient::SendQuery(uint32_t                           aChannelMask,
diff --git a/src/core/meshcop/joiner.cpp b/src/core/meshcop/joiner.cpp
index c3d223cd3..36345f07c 100644
--- a/src/core/meshcop/joiner.cpp
+++ b/src/core/meshcop/joiner.cpp
@@ -65,7 +65,7 @@ Joiner::Joiner(Instance &aInstance)
     , mJoinerEntrust(OT_URI_PATH_JOINER_ENTRUST, &Joiner::HandleJoinerEntrust, this)
 {
     memset(mJoinerRouters, 0, sizeof(mJoinerRouters));
-    IgnoreError(Get<Coap::Coap>().AddResource(mJoinerEntrust));
+    Get<Coap::Coap>().AddResource(mJoinerEntrust);
 }
 
 void Joiner::GetJoinerId(Mac::ExtAddress &aJoinerId) const
diff --git a/src/core/meshcop/joiner_router.cpp b/src/core/meshcop/joiner_router.cpp
index 5d0e4587e..227415457 100644
--- a/src/core/meshcop/joiner_router.cpp
+++ b/src/core/meshcop/joiner_router.cpp
@@ -63,7 +63,7 @@ JoinerRouter::JoinerRouter(Instance &aInstance)
     , mIsJoinerPortConfigured(false)
     , mExpectJoinEntRsp(false)
 {
-    IgnoreError(Get<Coap::Coap>().AddResource(mRelayTransmit));
+    Get<Coap::Coap>().AddResource(mRelayTransmit);
 }
 
 void JoinerRouter::HandleStateChanged(Notifier::Callback &aCallback, otChangedFlags aFlags)
diff --git a/src/core/meshcop/meshcop_leader.cpp b/src/core/meshcop/meshcop_leader.cpp
index 629acc392..9bd9a6d82 100644
--- a/src/core/meshcop/meshcop_leader.cpp
+++ b/src/core/meshcop/meshcop_leader.cpp
@@ -60,8 +60,8 @@ Leader::Leader(Instance &aInstance)
     , mDelayTimerMinimal(DelayTimerTlv::kDelayTimerMinimal)
     , mSessionId(Random::NonCrypto::GetUint16())
 {
-    IgnoreError(Get<Coap::Coap>().AddResource(mPetition));
-    IgnoreError(Get<Coap::Coap>().AddResource(mKeepAlive));
+    Get<Coap::Coap>().AddResource(mPetition);
+    Get<Coap::Coap>().AddResource(mKeepAlive);
 }
 
 void Leader::HandlePetition(void *aContext, otMessage *aMessage, const otMessageInfo *aMessageInfo)
diff --git a/src/core/meshcop/panid_query_client.cpp b/src/core/meshcop/panid_query_client.cpp
index 7eb0526d5..1fa2dea4a 100644
--- a/src/core/meshcop/panid_query_client.cpp
+++ b/src/core/meshcop/panid_query_client.cpp
@@ -54,7 +54,7 @@ PanIdQueryClient::PanIdQueryClient(Instance &aInstance)
     , mContext(NULL)
     , mPanIdQuery(OT_URI_PATH_PANID_CONFLICT, &PanIdQueryClient::HandleConflict, this)
 {
-    IgnoreError(Get<Coap::Coap>().AddResource(mPanIdQuery));
+    Get<Coap::Coap>().AddResource(mPanIdQuery);
 }
 
 otError PanIdQueryClient::SendQuery(uint16_t                            aPanId,
diff --git a/src/core/thread/address_resolver.cpp b/src/core/thread/address_resolver.cpp
index 6547526d5..113e281cc 100644
--- a/src/core/thread/address_resolver.cpp
+++ b/src/core/thread/address_resolver.cpp
@@ -71,9 +71,9 @@ AddressResolver::AddressResolver(Instance &aInstance)
         mUnusedList.Push(*entry);
     }
 
-    IgnoreError(Get<Coap::Coap>().AddResource(mAddressError));
-    IgnoreError(Get<Coap::Coap>().AddResource(mAddressQuery));
-    IgnoreError(Get<Coap::Coap>().AddResource(mAddressNotification));
+    Get<Coap::Coap>().AddResource(mAddressError);
+    Get<Coap::Coap>().AddResource(mAddressQuery);
+    Get<Coap::Coap>().AddResource(mAddressNotification);
 
     IgnoreError(Get<Ip6::Icmp>().RegisterHandler(mIcmpHandler));
 }
diff --git a/src/core/thread/announce_begin_server.cpp b/src/core/thread/announce_begin_server.cpp
index fa808d35f..c37d567e3 100644
--- a/src/core/thread/announce_begin_server.cpp
+++ b/src/core/thread/announce_begin_server.cpp
@@ -51,7 +51,7 @@ AnnounceBeginServer::AnnounceBeginServer(Instance &aInstance)
     : AnnounceSenderBase(aInstance, &AnnounceBeginServer::HandleTimer)
     , mAnnounceBegin(OT_URI_PATH_ANNOUNCE_BEGIN, &AnnounceBeginServer::HandleRequest, this)
 {
-    IgnoreError(Get<Coap::Coap>().AddResource(mAnnounceBegin));
+    Get<Coap::Coap>().AddResource(mAnnounceBegin);
 }
 
 void AnnounceBeginServer::SendAnnounce(uint32_t aChannelMask, uint8_t aCount, uint16_t aPeriod)
diff --git a/src/core/thread/energy_scan_server.cpp b/src/core/thread/energy_scan_server.cpp
index 0ef750036..67e309c3b 100644
--- a/src/core/thread/energy_scan_server.cpp
+++ b/src/core/thread/energy_scan_server.cpp
@@ -59,7 +59,7 @@ EnergyScanServer::EnergyScanServer(Instance &aInstance)
     , mNotifierCallback(aInstance, &EnergyScanServer::HandleStateChanged, this)
     , mEnergyScan(OT_URI_PATH_ENERGY_SCAN, &EnergyScanServer::HandleRequest, this)
 {
-    IgnoreError(Get<Coap::Coap>().AddResource(mEnergyScan));
+    Get<Coap::Coap>().AddResource(mEnergyScan);
 }
 
 void EnergyScanServer::HandleRequest(void *aContext, otMessage *aMessage, const otMessageInfo *aMessageInfo)
diff --git a/src/core/thread/mle_router.cpp b/src/core/thread/mle_router.cpp
index 3380d70af..90b4f7ca3 100644
--- a/src/core/thread/mle_router.cpp
+++ b/src/core/thread/mle_router.cpp
@@ -356,8 +356,8 @@ void MleRouter::SetStateLeader(uint16_t aRloc16)
     Get<NetworkData::Leader>().Start();
     Get<MeshCoP::ActiveDataset>().StartLeader();
     Get<MeshCoP::PendingDataset>().StartLeader();
-    IgnoreError(Get<Coap::Coap>().AddResource(mAddressSolicit));
-    IgnoreError(Get<Coap::Coap>().AddResource(mAddressRelease));
+    Get<Coap::Coap>().AddResource(mAddressSolicit);
+    Get<Coap::Coap>().AddResource(mAddressRelease);
     Get<Ip6::Ip6>().SetForwardingEnabled(true);
     Get<Ip6::Mpl>().SetTimerExpirations(kMplRouterDataMessageTimerExpirations);
     Get<Mac::Mac>().SetBeaconEnabled(true);
diff --git a/src/core/thread/network_data_leader_ftd.cpp b/src/core/thread/network_data_leader_ftd.cpp
index fb690bc76..6a3876aed 100644
--- a/src/core/thread/network_data_leader_ftd.cpp
+++ b/src/core/thread/network_data_leader_ftd.cpp
@@ -76,9 +76,9 @@ void Leader::Reset(void)
 
 void Leader::Start(void)
 {
-    IgnoreError(Get<Coap::Coap>().AddResource(mServerData));
-    IgnoreError(Get<Coap::Coap>().AddResource(mCommissioningDataGet));
-    IgnoreError(Get<Coap::Coap>().AddResource(mCommissioningDataSet));
+    Get<Coap::Coap>().AddResource(mServerData);
+    Get<Coap::Coap>().AddResource(mCommissioningDataGet);
+    Get<Coap::Coap>().AddResource(mCommissioningDataSet);
 }
 
 void Leader::Stop(void)
diff --git a/src/core/thread/network_diagnostic.cpp b/src/core/thread/network_diagnostic.cpp
index 29998e417..1f3933408 100644
--- a/src/core/thread/network_diagnostic.cpp
+++ b/src/core/thread/network_diagnostic.cpp
@@ -63,10 +63,10 @@ NetworkDiagnostic::NetworkDiagnostic(Instance &aInstance)
     , mReceiveDiagnosticGetCallback(NULL)
     , mReceiveDiagnosticGetCallbackContext(NULL)
 {
-    IgnoreError(Get<Coap::Coap>().AddResource(mDiagnosticGetRequest));
-    IgnoreError(Get<Coap::Coap>().AddResource(mDiagnosticGetQuery));
-    IgnoreError(Get<Coap::Coap>().AddResource(mDiagnosticGetAnswer));
-    IgnoreError(Get<Coap::Coap>().AddResource(mDiagnosticReset));
+    Get<Coap::Coap>().AddResource(mDiagnosticGetRequest);
+    Get<Coap::Coap>().AddResource(mDiagnosticGetQuery);
+    Get<Coap::Coap>().AddResource(mDiagnosticGetAnswer);
+    Get<Coap::Coap>().AddResource(mDiagnosticReset);
 }
 
 void NetworkDiagnostic::SetReceiveDiagnosticGetCallback(otReceiveDiagnosticGetCallback aCallback,
diff --git a/src/core/thread/panid_query_server.cpp b/src/core/thread/panid_query_server.cpp
index 8e54923b9..55062e9b8 100644
--- a/src/core/thread/panid_query_server.cpp
+++ b/src/core/thread/panid_query_server.cpp
@@ -53,7 +53,7 @@ PanIdQueryServer::PanIdQueryServer(Instance &aInstance)
     , mTimer(aInstance, &PanIdQueryServer::HandleTimer, this)
     , mPanIdQuery(OT_URI_PATH_PANID_QUERY, &PanIdQueryServer::HandleQuery, this)
 {
-    IgnoreError(Get<Coap::Coap>().AddResource(mPanIdQuery));
+    Get<Coap::Coap>().AddResource(mPanIdQuery);
 }
 
 void PanIdQueryServer::HandleQuery(void *aContext, otMessage *aMessage, const otMessageInfo *aMessageInfo)