diff --git a/src/init.cpp b/src/init.cpp
--- a/src/init.cpp
+++ b/src/init.cpp
@@ -27,6 +27,7 @@
 #include <net_processing.h>
 #include <netbase.h>
 #include <policy/policy.h>
+#include <rpc/blockchain.h>
 #include <rpc/register.h>
 #include <rpc/server.h>
 #include <scheduler.h>
diff --git a/src/rest.cpp b/src/rest.cpp
--- a/src/rest.cpp
+++ b/src/rest.cpp
@@ -62,9 +62,6 @@
     }
 };
 
-extern UniValue mempoolInfoToJSON();
-extern UniValue mempoolToJSON(bool fVerbose = false);
-
 static bool RESTERR(HTTPRequest *req, enum HTTPStatusCode status,
                     std::string message) {
     req->WriteHeader("Content-Type", "text/plain");
diff --git a/src/rpc/blockchain.h b/src/rpc/blockchain.h
--- a/src/rpc/blockchain.h
+++ b/src/rpc/blockchain.h
@@ -14,11 +14,29 @@
 
 UniValue getblockchaininfo(const Config &config, const JSONRPCRequest &request);
 
+/**
+ * Get the difficulty of the net wrt the given block index, or the chain tip
+ * if not provided.
+ *
+ * @return A floating point number that is a multiple of the main net minimum
+ * difficulty (4295032833 hashes).
+ */
 double GetDifficulty(const CBlockIndex *blockindex);
 
+/** Callback for when block tip changed. */
+void RPCNotifyBlockChange(bool ibd, const CBlockIndex *pindex);
+
+/** Block description to JSON */
 UniValue blockToJSON(const Config &config, const CBlock &block,
                      const CBlockIndex *blockindex, bool txDetails = false);
 
+/** Mempool information to JSON */
+UniValue mempoolInfoToJSON();
+
+/** Mempool to JSON */
+UniValue mempoolToJSON(bool fVerbose = false);
+
+/** Block header to JSON */
 UniValue blockheaderToJSON(const CBlockIndex *blockindex);
 
 #endif // BITCOIN_RPCBLOCKCHAIN_H
diff --git a/src/rpc/blockchain.cpp b/src/rpc/blockchain.cpp
--- a/src/rpc/blockchain.cpp
+++ b/src/rpc/blockchain.cpp
@@ -471,7 +471,7 @@
     info.pushKV("depends", depends);
 }
 
-UniValue mempoolToJSON(bool fVerbose = false) {
+UniValue mempoolToJSON(bool fVerbose) {
     if (fVerbose) {
         LOCK(g_mempool.cs);
         UniValue o(UniValue::VOBJ);
diff --git a/src/rpc/server.h b/src/rpc/server.h
--- a/src/rpc/server.h
+++ b/src/rpc/server.h
@@ -281,7 +281,6 @@
 void StopRPC();
 std::string JSONRPCExecBatch(Config &config, RPCServer &rpcServer,
                              const JSONRPCRequest &req, const UniValue &vReq);
-void RPCNotifyBlockChange(bool ibd, const CBlockIndex *);
 
 /**
  * Retrieves any serialization flags requested in command line argument