diff --git a/tools/ldb.cc b/tools/ldb.cc
index 56e3d9670..d26a491e0 100644
--- a/tools/ldb.cc
+++ b/tools/ldb.cc
@@ -67,7 +67,7 @@ public:
     }
 
     LDBCommand* cmdObj = LDBCommand::InitFromCmdLineArgs(argc, argv);
-    if (cmdObj == NULL) {
+    if (cmdObj == nullptr) {
       fprintf(stderr, "Unknown command\n");
       PrintHelp(argv[0]);
       exit(1);
diff --git a/tools/reduce_levels_test.cc b/tools/reduce_levels_test.cc
index 1e48e296e..8f2a4ce17 100644
--- a/tools/reduce_levels_test.cc
+++ b/tools/reduce_levels_test.cc
@@ -18,7 +18,7 @@ public:
   ReduceLevelTest() {
     dbname_ = test::TmpDir() + "/db_reduce_levels_test";
     DestroyDB(dbname_, Options());
-    db_ = NULL;
+    db_ = nullptr;
   }
 
   Status OpenDB(bool create_if_missing, int levels,
@@ -41,7 +41,7 @@ public:
   }
 
   Status CompactMemTable() {
-    if (db_ == NULL) {
+    if (db_ == nullptr) {
       return Status::InvalidArgument("DB not opened.");
     }
     DBImpl* db_impl = reinterpret_cast<DBImpl*>(db_);
@@ -49,9 +49,9 @@ public:
   }
 
   void CloseDB() {
-    if (db_ != NULL) {
+    if (db_ != nullptr) {
       delete db_;
-      db_ = NULL;
+      db_ = nullptr;
     }
   }
 
diff --git a/tools/sst_dump.cc b/tools/sst_dump.cc
index 7297571b2..f24e148d2 100644
--- a/tools/sst_dump.cc
+++ b/tools/sst_dump.cc
@@ -22,7 +22,7 @@ namespace leveldb {
 
 class SstFileReader {
 public:
-  SstFileReader(std::string file_name,
+  explicit SstFileReader(std::string file_name,
                 bool verify_checksum = false,
                 bool output_hex = false);
   Status ReadSequential(bool print_kv, uint64_t read_num = -1);
@@ -95,7 +95,7 @@ static void print_help() {
 
 int main(int argc, char** argv) {
 
-  const char* dir_or_file = NULL;
+  const char* dir_or_file = nullptr;
   uint64_t read_num = -1;
   std::string command;
 
@@ -121,7 +121,7 @@ int main(int argc, char** argv) {
     }
   }
 
-  if(dir_or_file == NULL) {
+  if(dir_or_file == nullptr) {
     print_help();
     exit(1);
   }