diff --git a/src/interfaces/README.md b/src/interfaces/README.md
--- a/src/interfaces/README.md
+++ b/src/interfaces/README.md
@@ -2,9 +2,9 @@
 
 The following interfaces are defined here:
 
-* [`Chain`](chain.h) — used by wallet to access blockchain and mempool state. Added in [#10973](https://github.com/bitcoin/bitcoin/pull/10973).
+* [`Chain`](chain.h) — used by wallet to access blockchain and mempool state. Added in [#14437](https://github.com/bitcoin/bitcoin/pull/14437), [#14711](https://github.com/bitcoin/bitcoin/pull/14711), [#15288](https://github.com/bitcoin/bitcoin/pull/15288), and [#10973](https://github.com/bitcoin/bitcoin/pull/10973).
 
-* [`ChainClient`](chain.h) — used by node to start & stop `Chain` clients. Added in [#10973](https://github.com/bitcoin/bitcoin/pull/10973).
+* [`ChainClient`](chain.h) — used by node to start & stop `Chain` clients. Added in [#14437](https://github.com/bitcoin/bitcoin/pull/14437).
 
 * [`Node`](node.h) — used by GUI to start & stop bitcoin node. Added in [#10244](https://github.com/bitcoin/bitcoin/pull/10244).
 
diff --git a/src/interfaces/chain.h b/src/interfaces/chain.h
--- a/src/interfaces/chain.h
+++ b/src/interfaces/chain.h
@@ -30,7 +30,27 @@
 
 class Wallet;
 
-//! Interface for giving wallet processes access to blockchain state.
+//! Interface giving clients (wallet processes, maybe other analysis tools in
+//! the future) ability to access to the chain state, receive notifications,
+//! estimate fees, and submit transactions.
+//!
+//! TODO: Current chain methods are too low level, exposing too much of the
+//! internal workings of the bitcoin node, and not being very convenient to use.
+//! Chain methods should be cleaned up and simplified over time. Examples:
+//!
+//! * The Chain::lock() method, which lets clients delay chain tip updates
+//!   should be removed when clients are able to respond to updates
+//!   asynchronously
+//!   (https://github.com/bitcoin/bitcoin/pull/10973#issuecomment-380101269).
+//!
+//! * The relayTransactions() and submitToMemoryPool() methods could be replaced
+//!   with a higher-level broadcastTransaction method
+//!   (https://github.com/bitcoin/bitcoin/pull/14978#issuecomment-459373984).
+//!
+//! * The initMessages() and loadWallet() methods which the wallet uses to send
+//!   notifications to the GUI should go away when GUI and wallet can directly
+//!   communicate with each other without going through the node
+//!   (https://github.com/bitcoin/bitcoin/pull/15288#discussion_r253321096).
 class Chain {
 public:
     virtual ~Chain() {}
@@ -163,8 +183,8 @@
     //! Relay transaction.
     virtual void relayTransaction(const TxId &txid) = 0;
 
-    //! Check chain limits.
-    virtual bool checkChainLimits(CTransactionRef tx) = 0;
+    //! Check if transaction will pass the mempool's chain limits.
+    virtual bool checkChainLimits(const CTransactionRef &tx) = 0;
 
     //! Get node max tx fee setting (-maxtxfee).
     //! This could be replaced by a per-wallet max fee, as proposed at
diff --git a/src/interfaces/chain.cpp b/src/interfaces/chain.cpp
--- a/src/interfaces/chain.cpp
+++ b/src/interfaces/chain.cpp
@@ -205,9 +205,8 @@
         }
         bool hasDescendantsInMempool(const TxId &txid) override {
             LOCK(::g_mempool.cs);
-            auto it_mp = ::g_mempool.mapTx.find(txid);
-            return it_mp != ::g_mempool.mapTx.end() &&
-                   it_mp->GetCountWithDescendants() > 1;
+            auto it = ::g_mempool.GetIter(txid);
+            return it && (*it)->GetCountWithDescendants() > 1;
         }
         void relayTransaction(const TxId &txid) override {
             CInv inv(MSG_TX, txid);
@@ -218,7 +217,7 @@
                                     size_t &descendants) override {
             ::g_mempool.GetTransactionAncestry(txid, ancestors, descendants);
         }
-        bool checkChainLimits(CTransactionRef tx) override {
+        bool checkChainLimits(const CTransactionRef &tx) override {
             LockPoints lp;
             CTxMemPoolEntry entry(tx, Amount(), 0, 0, false, 0, lp);
             CTxMemPool::setEntries ancestors;