diff --git a/src/main/scala/com/fluency03/blockchain/api/actors/BlocksActor.scala b/src/main/scala/com/fluency03/blockchain/api/actors/BlocksActor.scala
index ce03d09..a10b252 100644
--- a/src/main/scala/com/fluency03/blockchain/api/actors/BlocksActor.scala
+++ b/src/main/scala/com/fluency03/blockchain/api/actors/BlocksActor.scala
@@ -26,7 +26,7 @@ class BlocksActor extends ActorSupport {
   val transActor: ActorSelection = context.actorSelection(PARENT_UP + TRANS_ACTOR_NAME)
 
   // TODO (Chang): need persistence
-  var blocks = mutable.Map.empty[String, Block]
+  var blocksPool = mutable.Map.empty[String, Block]
 
   def receive: Receive = {
     case GetBlocks => onGetBlocks()
@@ -46,24 +46,25 @@ class BlocksActor extends ActorSupport {
    *
    */
 
-  private[this] def onGetBlocks(): Unit = sender() ! blocks.values.toSeq
-  private[this] def onGetBlocks(hashes: Set[String]): Unit = sender() ! blocks.filterKeys(
+  private[this] def onGetBlocks(): Unit = sender() ! blocksPool.values.toSeq
+
+  private[this] def onGetBlocks(hashes: Set[String]): Unit = sender() ! blocksPool.filterKeys(
     k => hashes.contains(k)
   ).values.toSeq
 
   private[this] def onCreateBlock(block: Block): Unit = {
-    if (blocks.contains(block.hash)) sender() ! FailureMsg(s"Block ${block.hash} already exists.")
+    if (blocksPool.contains(block.hash)) sender() ! FailureMsg(s"Block ${block.hash} already exists.")
     else {
-      blocks += (block.hash -> block)
+      blocksPool += (block.hash -> block)
       sender() ! SuccessMsg(s"Block ${block.hash} created.")
     }
   }
 
-  private[this] def onGetBlock(hash: String): Unit = sender() ! blocks.get(hash)
+  private[this] def onGetBlock(hash: String): Unit = sender() ! blocksPool.get(hash)
 
   private[this] def onDeleteBlock(hash: String): Unit = {
-    if (blocks.contains(hash)) {
-      blocks -= hash
+    if (blocksPool.contains(hash)) {
+      blocksPool -= hash
       sender() ! SuccessMsg(s"Block $hash deleted.")
     } else sender() ! FailureMsg(s"Block $hash does not exist.")
   }
diff --git a/src/main/scala/com/fluency03/blockchain/api/actors/NetworkActor.scala b/src/main/scala/com/fluency03/blockchain/api/actors/NetworkActor.scala
index bd953f1..c953beb 100644
--- a/src/main/scala/com/fluency03/blockchain/api/actors/NetworkActor.scala
+++ b/src/main/scala/com/fluency03/blockchain/api/actors/NetworkActor.scala
@@ -32,6 +32,13 @@ class NetworkActor extends ActorSupport {
 
   // TODO (Chang): need persistence
 
+  /**
+   * TODO (Chang):
+   *  - Remove wallet
+   *  - Sign transaction
+   *
+   */
+
   def receive: Receive = {
     case GetNetwork => onGetNetwork()
     case GetPeers => onGetPeers()
diff --git a/src/main/scala/com/fluency03/blockchain/api/actors/PeerActor.scala b/src/main/scala/com/fluency03/blockchain/api/actors/PeerActor.scala
index bcde51b..92b1d2d 100644
--- a/src/main/scala/com/fluency03/blockchain/api/actors/PeerActor.scala
+++ b/src/main/scala/com/fluency03/blockchain/api/actors/PeerActor.scala
@@ -27,6 +27,13 @@ class PeerActor extends ActorSupport {
   val wallets = mutable.Map.empty[String, Wallet]
   val others = mutable.Map.empty[String, Peer]
 
+  /**
+   * TODO (Chang):
+   *  - Remove wallet
+   *  - Sign transactions
+   *
+   */
+
   def receive: Receive = {
     case GetPublicKeys => sender() ! wallets.values.map(_.address).toSet
     case CreateWallet => sender() ! addWallet()
diff --git a/src/main/scala/com/fluency03/blockchain/api/actors/TransactionsActor.scala b/src/main/scala/com/fluency03/blockchain/api/actors/TransactionsActor.scala
index b644aa8..1fc0699 100644
--- a/src/main/scala/com/fluency03/blockchain/api/actors/TransactionsActor.scala
+++ b/src/main/scala/com/fluency03/blockchain/api/actors/TransactionsActor.scala
@@ -22,13 +22,20 @@ class TransactionsActor extends ActorSupport {
   override def postStop(): Unit = log.info("{} stopped!", this.getClass.getSimpleName)
 
   // TODO (Chang): need persistence
-  val currentTransactions: mutable.Map[String, Transaction] = mutable.Map.empty[String, Transaction]
+  val transPool: mutable.Map[String, Transaction] = mutable.Map.empty[String, Transaction]
   val uTxOs: mutable.Map[Outpoint, TxOut] = mutable.Map.empty[Outpoint, TxOut]
 
   val blockchainActor: ActorSelection = context.actorSelection(PARENT_UP + BLOCKCHAIN_ACTOR_NAME)
   val blockActor: ActorSelection = context.actorSelection(PARENT_UP + BLOCKS_ACTOR_NAME)
   val networkActor: ActorSelection = context.actorSelection(PARENT_UP + NETWORK_ACTOR_NAME)
 
+  /**
+   * TODO (Chang):
+   *  - Update transaction
+   *  - Sign transaction
+   *
+   */
+
   def receive: Receive = {
     case GetTransactions => onGetTransactions()
     case GetTransactions(ids) => onGetTransactions(ids)
@@ -38,25 +45,25 @@ class TransactionsActor extends ActorSupport {
     case _ => unhandled _
   }
 
-  private def onGetTransactions(): Unit = sender() ! currentTransactions.values.toSeq
+  private def onGetTransactions(): Unit = sender() ! transPool.values.toSeq
 
-  private def onGetTransactions(ids: Set[String]): Unit = sender() ! currentTransactions.filterKeys(
+  private def onGetTransactions(ids: Set[String]): Unit = sender() ! transPool.filterKeys(
     k => ids.contains(k)
   ).values.toSeq
 
   private def onCreateTransaction(tx: Transaction): Unit = {
-    if (currentTransactions.contains(tx.id)) sender() ! FailureMsg(s"Transaction ${tx.id} already exists.")
+    if (transPool.contains(tx.id)) sender() ! FailureMsg(s"Transaction ${tx.id} already exists.")
     else {
-      currentTransactions += (tx.id -> tx)
+      transPool += (tx.id -> tx)
       sender() ! SuccessMsg(s"Transaction ${tx.id} created.")
     }
   }
 
-  private def onGetTransaction(id: String): Unit = sender() ! currentTransactions.get(id)
+  private def onGetTransaction(id: String): Unit = sender() ! transPool.get(id)
 
   private def onDeleteTransaction(id: String): Unit =
-    if (currentTransactions contains id) {
-      currentTransactions -= id
+    if (transPool contains id) {
+      transPool -= id
       sender() ! SuccessMsg(s"Transaction $id deleted.")
     } else sender() ! FailureMsg(s"Transaction $id does not exist.")
 
diff --git a/src/main/scala/com/fluency03/blockchain/api/routes/NetworkRoutes.scala b/src/main/scala/com/fluency03/blockchain/api/routes/NetworkRoutes.scala
index 12f4a3e..d4f301a 100644
--- a/src/main/scala/com/fluency03/blockchain/api/routes/NetworkRoutes.scala
+++ b/src/main/scala/com/fluency03/blockchain/api/routes/NetworkRoutes.scala
@@ -20,6 +20,12 @@ trait NetworkRoutes extends RoutesSupport {
 
   def networkActor: ActorRef
 
+  /**
+   * TODO (Chang):
+   *  - Sign transaction
+   *
+   */
+
   lazy val networkRoutes: Route =
     path(NETWORK) {
       get {
diff --git a/src/main/scala/com/fluency03/blockchain/api/routes/TransactionRoutes.scala b/src/main/scala/com/fluency03/blockchain/api/routes/TransactionRoutes.scala
index ae24724..4f63ace 100644
--- a/src/main/scala/com/fluency03/blockchain/api/routes/TransactionRoutes.scala
+++ b/src/main/scala/com/fluency03/blockchain/api/routes/TransactionRoutes.scala
@@ -20,6 +20,13 @@ trait TransactionRoutes extends RoutesSupport {
 
   def transActor: ActorRef
 
+  /**
+   * TODO (Chang):
+   *  - Update transaction
+   *  - Sign transaction
+   *
+   */
+
   lazy val transRoutes: Route =
     path(TRANSACTIONS) {
       parameters( 'ids.as(CsvSeq[String]) ? ) { ids =>