diff --git a/README.cn.md b/README.cn.md
index 5da482d5943664a9bc4920e890c9c113f5d12e6f..9236024f6846005884cac0b363383121763cbf57 100644
--- a/README.cn.md
+++ b/README.cn.md
@@ -95,14 +95,14 @@ for step in range(100):
 #include "visualdl/sdk.h"
 
 namespace vs = visualdl;
-namepsace cp = visualdl::components;
+namespace cp = visualdl::components;
 
 int main() {
   const std::string dir = "./tmp";
   vs::LogWriter logger(dir, 10);
 
   logger.SetMode("train");
-  auto tablet = logger.NewTablet("scalars/scalar0");
+  auto tablet = logger.AddTablet("scalars/scalar0");
 
   cp::Scalar<float> scalar0(tablet);
 
diff --git a/docs/README.md b/docs/README.md
index 40429233175c7ed1445557b5c387324dd4d605a6..8825363c41c2002fd309def4b17b453a6b1bd755 100644
--- a/docs/README.md
+++ b/docs/README.md
@@ -81,14 +81,14 @@ The same code for C++ SDK in the above Python SDK is as follows
 #include "visualdl/sdk.h"
 
 namespace vs = visualdl;
-namepsace cp = visualdl::components;
+namespace cp = visualdl::components;
 
 int main() {
   const std::string dir = "./tmp";
   vs::LogWriter logger(dir, 10);
   
   logger.SetMode("train");
-  auto tablet = logger.NewTablet("scalars/scalar0");
+  auto tablet = logger.AddTablet("scalars/scalar0");
   
   cp::Scalar<float> scalar0(tablet);
   
diff --git a/visualdl/logic/sdk.cc b/visualdl/logic/sdk.cc
index 7436bc1f9410a77e3216fa7918aa60c99a1a521a..864b4598e11a3135a2be867d4c5896a0194707f6 100644
--- a/visualdl/logic/sdk.cc
+++ b/visualdl/logic/sdk.cc
@@ -30,6 +30,11 @@ namespace visualdl {
 std::string g_log_dir;
 
 LogWriter LogWriter::AsMode(const std::string& mode) {
+  for (auto ch : "%/") {
+    CHECK(mode.find(ch) == std::string::npos)
+      << "character "<< ch << " is a reserved word, it is not allowed in mode.";
+  }
+
   LogWriter writer = *this;
   storage_.AddMode(mode);
   writer.mode_ = mode;
@@ -37,7 +42,9 @@ LogWriter LogWriter::AsMode(const std::string& mode) {
 }
 
 Tablet LogWriter::AddTablet(const std::string& tag) {
-  // TODO(ChunweiYan) add string check here.
+  CHECK(tag.find("%") == std::string::npos)
+      << "character % is a reserved word, it is not allowed in tag.";
+
   auto tmp = mode_ + "/" + tag;
   string::TagEncode(tmp);
   auto res = storage_.AddTablet(tmp);