diff --git a/src/main/java/io/iworkflow/core/Client.java b/src/main/java/io/iworkflow/core/Client.java
index 25f5a1e5..d6b73927 100644
--- a/src/main/java/io/iworkflow/core/Client.java
+++ b/src/main/java/io/iworkflow/core/Client.java
@@ -1,5 +1,9 @@
 package io.iworkflow.core;
 
+import io.iworkflow.core.exceptions.LongPollTimeoutException;
+import io.iworkflow.core.exceptions.NoRunningWorkflowException;
+import io.iworkflow.core.exceptions.WorkflowAlreadyStartedException;
+import io.iworkflow.core.exceptions.WorkflowNotExistsException;
 import io.iworkflow.core.mapper.StateMovementMapper;
 import io.iworkflow.core.persistence.PersistenceOptions;
 import io.iworkflow.gen.models.ErrorSubStatus;
@@ -65,6 +69,7 @@ public UnregisteredClient getUnregisteredClient() {
      * @param workflowId             is required
      * @param workflowTimeoutSeconds is required
      * @return runId
+     * @throws WorkflowAlreadyStartedException if the workflow is already started
      */
     public String startWorkflow(
             final Class<? extends ObjectWorkflow> workflowClass,
@@ -81,6 +86,7 @@ public String startWorkflow(
      * @param workflowTimeoutSeconds is required
      * @param input                  is optional, can be null
      * @return runId
+     * @throws WorkflowAlreadyStartedException if the workflow is already started
      */
     public String startWorkflow(
             final Class<? extends ObjectWorkflow> workflowClass,
@@ -99,6 +105,10 @@ public String startWorkflow(
      * @param input                  is optional, can be null
      * @param option                 is optional, can be null
      * @return runId
+     * @throws WorkflowAlreadyStartedException if the workflow is already started.
+     * If using WorkflowAlreadyStartedOptions in WorkflowOptions, the error will be ignored if ignoreAlreadyStartedError is true.
+     * If ignoreAlreadyStartedError is true and also requestId is set, the requestId will be used to identify the request. The error
+     * will only be thrown if the requestId is different from the requestId of the existing workflow.
      */
     public String startWorkflow(
             final Class<? extends ObjectWorkflow> workflowClass,
@@ -119,6 +129,10 @@ public String startWorkflow(
      * @param input                  is optional, can be null
      * @param options                is optional, can be null
      * @return runId
+     * @throws WorkflowAlreadyStartedException if the workflow is already started.
+     * If using WorkflowAlreadyStartedOptions in WorkflowOptions, the error will be ignored if ignoreAlreadyStartedError is true.
+     * If ignoreAlreadyStartedError is true and also requestId is set, the requestId will be used to identify the request. The error
+     * will only be thrown if the requestId is different from the requestId of the existing workflow.
      */
     public String startWorkflow(
             final String wfType,
@@ -257,9 +271,11 @@ private List<SearchAttribute> convertToSearchAttributeList(final Map<String, Sea
      * A long poll API to wait for the workflow completion.
      * Due to the limit of REST API, it will only wait for 30 seconds for the workflow to complete.
      * (configurable in ClientOptions.LongPollApiMaxWaitTimeSeconds)
-     * If the workflow is not COMPLETED, throw the {@link WorkflowUncompletedException}.
      *
      * @param workflowId    required, the workflowId
+     * @throws WorkflowUncompletedException if the workflow is not COMPLETED
+     * @throws WorkflowNotExistsException if the workflow is not existing
+     * @throws LongPollTimeoutException if the long poll timeout
      */
     public void waitForWorkflowCompletion(
             final String workflowId) {
@@ -277,6 +293,9 @@ public void waitForWorkflowCompletion(
      * @param workflowId    required, the workflowId
      * @param <T>           type of the output
      * @return the output result
+     * @throws WorkflowUncompletedException if the workflow is not COMPLETED
+     * @throws WorkflowNotExistsException if the workflow is not existing
+     * @throws LongPollTimeoutException if the long poll timeout
      */
     public <T> T waitForWorkflowCompletion(
             final Class<T> valueClass,
@@ -287,6 +306,14 @@ public <T> T waitForWorkflowCompletion(
     /**
      * Use {@link #waitForWorkflowCompletion(Class, String)} instead
      * It's just a renaming.
+     * @param <T> type of the output
+     * @param valueClass   required, the type class of the output
+     * @param workflowId   required, the workflowId
+     * @param workflowRunId optional, can be empty
+     * @return the output result
+     * @throws WorkflowUncompletedException if the workflow is not COMPLETED
+     * @throws WorkflowNotExistsException if the workflow is not existing
+     * @throws LongPollTimeoutException if the long poll timeout
      */
     @Deprecated
     public <T> T getSimpleWorkflowResultWithWait(
@@ -299,6 +326,13 @@ public <T> T getSimpleWorkflowResultWithWait(
     /**
      * Use {@link #waitForWorkflowCompletion(Class, String)} instead
      * It's just a renaming.
+     * @param <T> type of the output
+     * @param valueClass   required, the type class of the output
+     * @param workflowId   required, the workflowId
+     * @return the output result
+     * @throws WorkflowUncompletedException if the workflow is not COMPLETED
+     * @throws WorkflowNotExistsException if the workflow is not existing
+     * @throws LongPollTimeoutException if the long poll timeout
      */
     @Deprecated
     public <T> T getSimpleWorkflowResultWithWait(
@@ -310,14 +344,14 @@ public <T> T getSimpleWorkflowResultWithWait(
     /**
      * For most cases, a workflow only has one result(one completion state).
      * Use this API to retrieve the output of the state without waiting for the workflow to complete.
-     * If the workflow is not COMPLETED, throw the {@link WorkflowUncompletedException}.
-     * Else, return the same result as {@link #getSimpleWorkflowResultWithWait(Class, String, String)}.
      *
      * @param valueClass    required, the type class of the output
      * @param workflowId    required, the workflowId
      * @param workflowRunId optional, can be empty
      * @param <T>           type of the output
      * @return the output result
+     * @throws WorkflowUncompletedException if the workflow is not COMPLETED
+     * @throws WorkflowNotExistsException if the workflow is not existing
      */
     public <T> T tryGettingSimpleWorkflowResult(
             final Class<T> valueClass,
@@ -329,13 +363,13 @@ public <T> T tryGettingSimpleWorkflowResult(
     /**
      * For most cases, a workflow only has one result(one completion state).
      * Use this API to retrieve the output of the state without waiting for the workflow to complete.
-     * If the workflow is not COMPLETED, throw the {@link WorkflowUncompletedException}.
-     * Else, return the same result as {@link #getSimpleWorkflowResultWithWait(Class, String)}.
      *
      * @param valueClass    required, the type class of the output
      * @param workflowId    required, the workflowId
      * @param <T>           type of the output
      * @return the output result
+     * @throws WorkflowUncompletedException if the workflow is not COMPLETED
+     * @throws WorkflowNotExistsException if the workflow is not existing
      */
     public <T> T tryGettingSimpleWorkflowResult(
             final Class<T> valueClass,
@@ -346,11 +380,13 @@ public <T> T tryGettingSimpleWorkflowResult(
     /**
      * In some cases, a workflow may have more than one completion states.
      * Use this API to retrieve the output of the states with waiting for the workflow to complete.
-     * If the workflow is not COMPLETED, throw the {@link feign.FeignException.FeignClientException}.
      *
      * @param workflowId    required, the workflowId
      * @param workflowRunId optional, can be empty
      * @return a list of the state output for completion states. User code will figure how to use ObjectEncoder to decode the output
+     * @throws WorkflowUncompletedException if the workflow is not COMPLETED
+     * @throws WorkflowNotExistsException if the workflow is not existing
+     * @throws LongPollTimeoutException if the long poll timeout
      */
     public List<StateCompletionOutput> getComplexWorkflowResultWithWait(
             final String workflowId, final String workflowRunId) {
@@ -360,10 +396,12 @@ public List<StateCompletionOutput> getComplexWorkflowResultWithWait(
     /**
      * In some cases, a workflow may have more than one completion states.
      * Use this API to retrieve the output of the states with waiting for the workflow to complete.
-     * If the workflow is not COMPLETED, throw the {@link feign.FeignException.FeignClientException}.
      *
      * @param workflowId    required, the workflowId
      * @return a list of the state output for completion states. User code will figure how to use ObjectEncoder to decode the output
+     * @throws WorkflowUncompletedException if the workflow is not COMPLETED
+     * @throws WorkflowNotExistsException if the workflow is not existing
+     * @throws LongPollTimeoutException if the long poll timeout
      */
     public List<StateCompletionOutput> getComplexWorkflowResultWithWait(final String workflowId) {
         return getComplexWorkflowResultWithWait(workflowId, "");
@@ -372,12 +410,12 @@ public List<StateCompletionOutput> getComplexWorkflowResultWithWait(final String
     /**
      * In some cases, a workflow may have more than one completion states.
      * Use this API to retrieve the output of the states without waiting for the workflow to complete.
-     * If the workflow is not COMPLETED, throw the {@link WorkflowUncompletedException}.
-     * Else, return the same result as {@link #getComplexWorkflowResultWithWait(String, String)}.
      *
      * @param workflowId    required, the workflowId
      * @param workflowRunId optional, can be empty
      * @return a list of the state output for completion states. User code will figure how to use ObjectEncoder to decode the output
+     * @throws WorkflowUncompletedException if the workflow is not COMPLETED
+     * @throws WorkflowNotExistsException if the workflow is not existing
      */
     public List<StateCompletionOutput> tryGettingComplexWorkflowResult(
             final String workflowId, final String workflowRunId) {
@@ -387,11 +425,11 @@ public List<StateCompletionOutput> tryGettingComplexWorkflowResult(
     /**
      * In some cases, a workflow may have more than one completion states.
      * Use this API to retrieve the output of the states without waiting for the workflow to complete.
-     * If the workflow is not COMPLETED, throw the {@link WorkflowUncompletedException}.
-     * Else, return the same result as {@link #getComplexWorkflowResultWithWait(String)}.
      *
      * @param workflowId    required, the workflowId
      * @return a list of the state output for completion states. User code will figure how to use ObjectEncoder to decode the output
+     * @throws WorkflowUncompletedException if the workflow is not COMPLETED
+     * @throws WorkflowNotExistsException if the workflow is not existing
      */
     public List<StateCompletionOutput> tryGettingComplexWorkflowResult(final String workflowId) {
         return tryGettingComplexWorkflowResult(workflowId, "");
@@ -405,6 +443,7 @@ public List<StateCompletionOutput> tryGettingComplexWorkflowResult(final String
      * @param workflowRunId     optional, can be empty
      * @param signalChannelName required
      * @param signalValue       optional, can be null
+     * @throws NoRunningWorkflowException  if the workflow is not existing or not running
      */
     public void signalWorkflow(
             final Class<? extends ObjectWorkflow> workflowClass,
@@ -432,6 +471,7 @@ public void signalWorkflow(
      * @param workflowId        required
      * @param signalChannelName required
      * @param signalValue       optional, can be null
+     * @throws NoRunningWorkflowException  if the workflow is not existing or not running
      */
     public void signalWorkflow(
             final Class<? extends ObjectWorkflow> workflowClass,
@@ -446,6 +486,7 @@ public void signalWorkflow(
      * @param workflowRunId                 optional, can be empty
      * @param resetWorkflowTypeAndOptions   required, the combination parameter for reset
      * @return the new runId after reset
+     * @throws WorkflowNotExistsException  if the workflow is not existing
      */
     public String resetWorkflow(
             final String workflowId,
@@ -459,6 +500,7 @@ public String resetWorkflow(
      * @param workflowId                    required
      * @param resetWorkflowTypeAndOptions   required, the combination parameter for reset
      * @return the new runId after reset
+     * @throws WorkflowNotExistsException  if the workflow is not existing
      */
     public String resetWorkflow(
             final String workflowId,
@@ -473,6 +515,7 @@ public String resetWorkflow(
      * @param workflowId    required
      * @param workflowRunId optional, can be empty
      * @param options       optional, can be null. If not set, the workflow status will be CANCELED
+     * @throws NoRunningWorkflowException  if the workflow is not existing or not running
      */
     public void stopWorkflow(
             final String workflowId,
@@ -486,6 +529,7 @@ public void stopWorkflow(
      *
      * @param workflowId    required
      * @param options       optional, can be null. If not set, the workflow status will be CANCELED
+     * @throws NoRunningWorkflowException  if the workflow is not existing or not running
      */
     public void stopWorkflow(
             final String workflowId,
@@ -498,6 +542,7 @@ public void stopWorkflow(
      * The workflow status will be CANCELED
      *
      * @param workflowId    required
+     * @throws NoRunningWorkflowException  if the workflow is not existing or not running
      */
     public void stopWorkflow(final String workflowId) {
         stopWorkflow(workflowId, "", null);
@@ -511,6 +556,7 @@ public void stopWorkflow(final String workflowId) {
      * @param workflowRunId     optional, can be empty
      * @param keys              required, cannot be empty or null
      * @return the data attributes
+     * @throws WorkflowNotExistsException  if the workflow is not existing
      */
     public Map<String, Object> getWorkflowDataAttributes(
             final Class<? extends ObjectWorkflow> workflowClass,
@@ -531,6 +577,7 @@ public Map<String, Object> getWorkflowDataAttributes(
      * @param workflowId        required
      * @param keys              required, cannot be empty or null
      * @return the data attributes
+     * @throws WorkflowNotExistsException  if the workflow is not existing
      */
     public Map<String, Object> getWorkflowDataAttributes(
             final Class<? extends ObjectWorkflow> workflowClass,
@@ -546,6 +593,7 @@ public Map<String, Object> getWorkflowDataAttributes(
      * @param workflowId        required
      * @param workflowRunId     optional, can be empty
      * @return the data attributes
+     * @throws WorkflowNotExistsException  if the workflow is not existing
      */
     public Map<String, Object> getAllDataAttributes(
             final Class<? extends ObjectWorkflow> workflowClass,
@@ -560,6 +608,7 @@ public Map<String, Object> getAllDataAttributes(
      * @param workflowClass     required
      * @param workflowId        required
      * @return the data attributes
+     * @throws WorkflowNotExistsException  if the workflow is not existing
      */
     public Map<String, Object> getAllDataAttributes(
             final Class<? extends ObjectWorkflow> workflowClass,
@@ -622,6 +671,7 @@ private Map<String, Object> doGetWorkflowDataAttributes(
      * @param workflowId     required
      * @param workflowRunId  optional, can be empty
      * @param dataAttributes required
+     * @throws NoRunningWorkflowException  if the workflow is not existing or not running
      * */
     public void setWorkflowDataAttributes(
             final Class<? extends ObjectWorkflow> workflowClass,
@@ -637,6 +687,7 @@ public void setWorkflowDataAttributes(
      * @param workflowClass  required
      * @param workflowId     required
      * @param dataAttributes required
+     * @throws NoRunningWorkflowException  if the workflow is not existing or not running
      * */
     public void setWorkflowDataAttributes(
             final Class<? extends ObjectWorkflow> workflowClass,
@@ -766,6 +817,7 @@ public <T> T newRpcStub(Class<T> workflowClassForRpc, String workflowId) {
      * @param <I>           the input type
      * @param <O>           the output type
      * @return output
+     * @throws WorkflowNotExistsException  if the workflow is not existing, or not running to accept a write operation in RPC
      */
     public <I, O> O invokeRPC(RpcDefinitions.RpcFunc1<I, O> rpcStubMethod, I input) {
         return rpcStubMethod.execute(null, input, null, null);
@@ -779,6 +831,7 @@ public <I, O> O invokeRPC(RpcDefinitions.RpcFunc1<I, O> rpcStubMethod, I input)
      * @param <I>           the input type
      * @param <O>           the output type
      * @return              output
+     * @throws WorkflowNotExistsException  if the workflow is not existing, or not running to accept a write operation in RPC
      */
     public <I, O> O invokeRPC(RpcDefinitions.RpcFunc1NoPersistence<I, O> rpcStubMethod, I input) {
         return rpcStubMethod.execute(null, input, null);
@@ -790,6 +843,7 @@ public <I, O> O invokeRPC(RpcDefinitions.RpcFunc1NoPersistence<I, O> rpcStubMeth
      * @param rpcStubMethod the RPC method from stub created by {@link #newRpcStub(Class, String, String)}
      * @param <O>           the output type
      * @return output
+     * @throws WorkflowNotExistsException  if the workflow is not existing, or not running to accept a write operation in RPC
      */
     public <O> O invokeRPC(RpcDefinitions.RpcFunc0<O> rpcStubMethod) {
         return rpcStubMethod.execute(null, null, null);
@@ -801,6 +855,7 @@ public <O> O invokeRPC(RpcDefinitions.RpcFunc0<O> rpcStubMethod) {
      * @param rpcStubMethod the RPC method from stub created by {@link #newRpcStub(Class, String, String)}
      * @param <O>           the output type
      * @return output
+     * @throws WorkflowNotExistsException  if the workflow is not existing, or not running to accept a write operation in RPC
      */
     public <O> O invokeRPC(RpcDefinitions.RpcFunc0NoPersistence<O> rpcStubMethod) {
         return rpcStubMethod.execute(null, null);
@@ -812,6 +867,7 @@ public <O> O invokeRPC(RpcDefinitions.RpcFunc0NoPersistence<O> rpcStubMethod) {
      * @param rpcStubMethod the RPC method from stub created by {@link #newRpcStub(Class, String, String)}
      * @param input         the input of the RPC method
      * @param <I>           the input type
+     * @throws WorkflowNotExistsException  if the workflow is not existing, or not running to accept a write operation in RPC
      */
     public <I> void invokeRPC(RpcDefinitions.RpcProc1<I> rpcStubMethod, I input) {
         rpcStubMethod.execute(null, input, null, null);
@@ -823,6 +879,7 @@ public <I> void invokeRPC(RpcDefinitions.RpcProc1<I> rpcStubMethod, I input) {
      * @param rpcStubMethod the RPC method from stub created by {@link #newRpcStub(Class, String, String)}
      * @param input         the input of the RPC method
      * @param <I>           the input type
+     * @throws WorkflowNotExistsException  if the workflow is not existing, or not running to accept a write operation in RPC
      */
     public <I> void invokeRPC(RpcDefinitions.RpcProc1NoPersistence<I> rpcStubMethod, I input) {
         rpcStubMethod.execute(null, input, null);
@@ -832,6 +889,7 @@ public <I> void invokeRPC(RpcDefinitions.RpcProc1NoPersistence<I> rpcStubMethod,
      * invoking the RPC through RPC stub
      *
      * @param rpcStubMethod the RPC method from stub created by {@link #newRpcStub(Class, String, String)}
+     * @throws WorkflowNotExistsException  if the workflow is not existing, or not running to accept a write operation in RPC
      */
     public void invokeRPC(RpcDefinitions.RpcProc0 rpcStubMethod) {
         rpcStubMethod.execute(null, null, null);
@@ -841,6 +899,7 @@ public void invokeRPC(RpcDefinitions.RpcProc0 rpcStubMethod) {
      * invoking the RPC through RPC stub
      *
      * @param rpcStubMethod the RPC method from stub created by {@link #newRpcStub(Class, String, String)}
+     * @throws WorkflowNotExistsException  if the workflow is not existing, or not running to accept a write operation in RPC
      */
     public void invokeRPC(RpcDefinitions.RpcProc0NoPersistence rpcStubMethod) {
         rpcStubMethod.execute(null, null);
@@ -854,6 +913,7 @@ public void invokeRPC(RpcDefinitions.RpcProc0NoPersistence rpcStubMethod) {
      * @param workflowRunId     optional, can be empty
      * @param attributeKeys     required, cannot be empty or null
      * @return the search attributes
+     * @throws WorkflowNotExistsException  if the workflow is not existing
      */
     public Map<String, Object> getWorkflowSearchAttributes(
             final Class<? extends ObjectWorkflow> workflowClass,
@@ -873,6 +933,7 @@ public Map<String, Object> getWorkflowSearchAttributes(
      * @param workflowId        required
      * @param attributeKeys     required, cannot be empty or null
      * @return the search attributes
+     * @throws WorkflowNotExistsException  if the workflow is not existing
      */
     public Map<String, Object> getWorkflowSearchAttributes(
             final Class<? extends ObjectWorkflow> workflowClass,
@@ -888,6 +949,7 @@ public Map<String, Object> getWorkflowSearchAttributes(
      * @param workflowId        required
      * @param workflowRunId     optional, can be empty
      * @return the search attributes
+     * @throws WorkflowNotExistsException  if the workflow is not existing
      */
     public Map<String, Object> getAllSearchAttributes(
             final Class<? extends ObjectWorkflow> workflowClass,
@@ -903,6 +965,7 @@ public Map<String, Object> getAllSearchAttributes(
      * @param workflowClass    required
      * @param workflowId       required
      * @param searchAttributes required
+     * @throws NoRunningWorkflowException if the workflow is not existing or not running
      * */
     public void setWorkflowSearchAttributes(
             final Class<? extends ObjectWorkflow> workflowClass,
@@ -918,6 +981,7 @@ public void setWorkflowSearchAttributes(
      * @param workflowId       required
      * @param workflowRunId    optional, can be empty
      * @param searchAttributes required
+     * @throws NoRunningWorkflowException if the workflow is not existing or not running
      * */
     public void setWorkflowSearchAttributes(
             final Class<? extends ObjectWorkflow> workflowClass,
@@ -933,6 +997,7 @@ public void setWorkflowSearchAttributes(
      * @param workflowClass     required
      * @param workflowId        required
      * @return the search attributes
+     * @throws WorkflowNotExistsException  if the workflow is not existing
      */
     public Map<String, Object> getAllSearchAttributes(
             final Class<? extends ObjectWorkflow> workflowClass,
@@ -947,6 +1012,7 @@ public Map<String, Object> getAllSearchAttributes(
      * @param workflowId    required
      * @param workflowRunId optional, can be empty
      * @return the workflow's info
+     * @throws WorkflowNotExistsException  if the workflow is not existing
      */
     public WorkflowInfo describeWorkflow(
             final String workflowId,
@@ -963,6 +1029,7 @@ public WorkflowInfo describeWorkflow(
      *
      * @param workflowId    required
      * @return the workflow's info
+     * @throws WorkflowNotExistsException  if the workflow is not existing
      */
     public WorkflowInfo describeWorkflow(
             final String workflowId) {
@@ -1106,9 +1173,10 @@ public void skipTimer(
      * A long poll API to wait for the completion of the state. This only waits for the first completion.
      * Note 1 The stateCompletion to wait for is needed to registered on starting workflow due to limitation in https://github.com/indeedeng/iwf/issues/349
      * Note 2 The max polling time is configured as clientOptions as the Feign client timeout(default to 10s)
-     * If the state is not COMPLETED, throw the {@link ClientSideException} with the sub status of {@link ErrorSubStatus#LONG_POLL_TIME_OUT_SUB_STATUS}
      * @param workflowId the workflowId
      * @param stateClass the state class.
+     * @throws LongPollTimeoutException if the long poll timeout
+     * @throws WorkflowNotExistsException if the workflow is not existing
      */
     public void waitForStateExecutionCompletion(
             final String workflowId,
@@ -1124,6 +1192,8 @@ public void waitForStateExecutionCompletion(
      * @param workflowId the workflowId
      * @param stateClass the state class
      * @param waitForKey key provided by the client and to identity workflow
+     * @throws LongPollTimeoutException if the long poll timeout
+     * @throws WorkflowNotExistsException if the workflow is not existing
      */
     public void waitForStateExecutionCompletion(
             final String workflowId,
@@ -1141,6 +1211,8 @@ public void waitForStateExecutionCompletion(
      * @param workflowId the workflowId
      * @param stateClass the state class
      * @param stateExecutionNumber the state execution number. E.g. if it's 2, it means the 2nd execution of the state
+     * @throws LongPollTimeoutException if the long poll timeout
+     * @throws WorkflowNotExistsException if the workflow is not existing
      */
     public void waitForStateExecutionCompletion(
             final String workflowId,
diff --git a/src/main/java/io/iworkflow/core/Context.java b/src/main/java/io/iworkflow/core/Context.java
index 01a7e549..e4dbd9da 100644
--- a/src/main/java/io/iworkflow/core/Context.java
+++ b/src/main/java/io/iworkflow/core/Context.java
@@ -8,6 +8,10 @@
 public abstract class Context {
     public abstract Long getWorkflowStartTimestampSeconds();
 
+    /**
+     * @return the StateExecutionId.
+     * Only applicable for state methods (waitUntil or execute)
+     */
     public abstract Optional<String> getStateExecutionId();
 
     public abstract String getWorkflowRunId();
@@ -16,11 +20,20 @@ public abstract class Context {
 
     public abstract String getWorkflowType();
 
-    // this is the start time of the first attempt of the API call. It's from ScheduledTimestamp of Cadence/Temporal activity.GetInfo
-    // require server version 1.2.2+, return -1 if server version is lower
+    /**
+     * @return the start time of the first attempt of the state method invocation.
+     * Only applicable for state methods (waitUntil or execute)
+     */
     public abstract Optional<Long> getFirstAttemptTimestampSeconds();
 
-    // Attempt starts from 1, and increased by 1 for every retry if retry policy is specified. It's from Attempt of Cadence/Temporal activity.GetInfo
-    // require server version 1.2.2+, return -1 if server version is lower
+    /**
+     * @return attempt starts from 1, and increased by 1 for every retry if retry policy is specified.
+     */
     public abstract Optional<Integer> getAttempt();
+
+    /**
+     * @return the requestId that is used to start the child workflow from state method.
+     * Only applicable for state methods (waitUntil or execute)
+     */
+    public abstract Optional<String> getChildWorkflowRequestId();
 }
diff --git a/src/main/java/io/iworkflow/core/RPC.java b/src/main/java/io/iworkflow/core/RPC.java
index c85da78f..f8c921fc 100644
--- a/src/main/java/io/iworkflow/core/RPC.java
+++ b/src/main/java/io/iworkflow/core/RPC.java
@@ -38,6 +38,7 @@
      * Only used when workflow has enabled {@link PersistenceOptions} CachingPersistenceByMemo
      * By default, it's false for high throughput support
      * flip to true to bypass the caching for strong consistent reads
+     * @return true if bypass caching for strong consistency
      */
     boolean bypassCachingForStrongConsistency() default false;
 }
\ No newline at end of file
diff --git a/src/main/java/io/iworkflow/core/StateDecision.java b/src/main/java/io/iworkflow/core/StateDecision.java
index bd8c9276..aad6c674 100644
--- a/src/main/java/io/iworkflow/core/StateDecision.java
+++ b/src/main/java/io/iworkflow/core/StateDecision.java
@@ -182,7 +182,7 @@ public static <I> StateDecision singleNextState(final Class<? extends WorkflowSt
      * singleNextState as non-strongly typing required for input
      * @param stateClass required
      * @param stateInput optional, can be null
-     * @return
+     * @return state decision
      */
     public static StateDecision singleNextStateUntypedInput(final Class<? extends WorkflowState> stateClass, final Object stateInput) {
         return singleNextState(stateClass.getSimpleName(), stateInput, null);
diff --git a/src/main/java/io/iworkflow/core/WorkerService.java b/src/main/java/io/iworkflow/core/WorkerService.java
index ff4e2698..ee8c8e30 100644
--- a/src/main/java/io/iworkflow/core/WorkerService.java
+++ b/src/main/java/io/iworkflow/core/WorkerService.java
@@ -388,6 +388,7 @@ private Context fromIdlContext(final io.iworkflow.gen.models.Context context, fi
                 .workflowRunId(context.getWorkflowRunId())
                 .workflowStartTimestampSeconds(context.getWorkflowStartedTimestamp())
                 .stateExecutionId(Optional.ofNullable(context.getStateExecutionId()))
+                .childWorkflowRequestId(context.getWorkflowRunId()+"-"+context.getStateExecutionId())
                 .attempt(attempt)
                 .firstAttemptTimestampSeconds(firstAttemptTimestamp)
                 .build();
diff --git a/src/main/java/io/iworkflow/core/communication/Communication.java b/src/main/java/io/iworkflow/core/communication/Communication.java
index 748760d8..71d6ec8a 100644
--- a/src/main/java/io/iworkflow/core/communication/Communication.java
+++ b/src/main/java/io/iworkflow/core/communication/Communication.java
@@ -16,8 +16,7 @@ public interface Communication {
      * trigger new state movements as the RPC results
      * NOTE: closing workflows like completing/failing are not supported
      * NOTE: Only used in RPC -- cannot be used in state APIs
-     *
-     * @param stateMovements
+     * @param stateMovements the state movements to trigger
      */
     void triggerStateMovements(final StateMovement... stateMovements);
 }
diff --git a/src/main/java/io/iworkflow/core/exceptions/NoRunningWorkflowException.java b/src/main/java/io/iworkflow/core/exceptions/NoRunningWorkflowException.java
index 6bd94c9d..f20a8f04 100644
--- a/src/main/java/io/iworkflow/core/exceptions/NoRunningWorkflowException.java
+++ b/src/main/java/io/iworkflow/core/exceptions/NoRunningWorkflowException.java
@@ -2,7 +2,12 @@
 
 import io.iworkflow.core.ClientSideException;
 
-public class NoRunningWorkflowException extends WorkflowNotExistsOrOpenException {
+/**
+ * A friendly named exception to indicate that the workflow does not exist or exists but not running.
+ * It's the same as {@link WorkflowNotExistsException} but with a different name.
+ * It's subclass of {@link ClientSideException} with ErrorSubStatus.WORKFLOW_NOT_EXISTS_SUB_STATUS
+ */
+public class NoRunningWorkflowException extends WorkflowNotExistsException {
     public NoRunningWorkflowException(
             final ClientSideException exception) {
         super(exception);
diff --git a/src/main/java/io/iworkflow/core/exceptions/WorkflowNotExistsException.java b/src/main/java/io/iworkflow/core/exceptions/WorkflowNotExistsException.java
new file mode 100644
index 00000000..dd29852e
--- /dev/null
+++ b/src/main/java/io/iworkflow/core/exceptions/WorkflowNotExistsException.java
@@ -0,0 +1,14 @@
+package io.iworkflow.core.exceptions;
+
+import io.iworkflow.core.ClientSideException;
+
+/**
+ * A friendly named exception to indicate that the workflow does not exist
+ * It's subclass of {@link ClientSideException} with ErrorSubStatus.WORKFLOW_NOT_EXISTS_SUB_STATUS
+ */
+public class WorkflowNotExistsException extends ClientSideException {
+    public WorkflowNotExistsException(
+            final ClientSideException exception) {
+        super(exception);
+    }
+}
diff --git a/src/main/java/io/iworkflow/core/exceptions/WorkflowNotExistsOrOpenException.java b/src/main/java/io/iworkflow/core/exceptions/WorkflowNotExistsOrOpenException.java
deleted file mode 100644
index 94471233..00000000
--- a/src/main/java/io/iworkflow/core/exceptions/WorkflowNotExistsOrOpenException.java
+++ /dev/null
@@ -1,14 +0,0 @@
-package io.iworkflow.core.exceptions;
-
-import io.iworkflow.core.ClientSideException;
-
-/**
- * @deprecated Use NoRunningWorkflowException instead
- */
-@Deprecated
-public class WorkflowNotExistsOrOpenException extends ClientSideException {
-    public WorkflowNotExistsOrOpenException(
-            final ClientSideException exception) {
-        super(exception);
-    }
-}