diff --git a/README.md b/README.md
index 31d2778..837a854 100644
--- a/README.md
+++ b/README.md
@@ -21,6 +21,8 @@ The main feature is below.
     *   Not completed so far, though. 
     *   See [doc/cstdlib.md](doc/cstdlib.md) for the current status.
 *   KCCI also provides useful libraries by default like regex, zip, and so on.
+    *   See [doc/extension.md](doc/extension.md) for extended library interface.
+    *   See the [samples](samples) because there are some samples about how to use.
     *   Some libraries will be coming soon.
     *   Please let me know if you have library which you want to use.
 
diff --git a/doc/extension.md b/doc/extension.md
index 98a5f14..1421042 100644
--- a/doc/extension.md
+++ b/doc/extension.md
@@ -23,7 +23,7 @@
 #include <kcc/bigint.h>
 ```
 
-*   [Big Integer](extensios/bigint.md)
+*   [Big Integer](extensions/bigint.md)
 
 ---
 
@@ -33,7 +33,7 @@
 #include <kcc/regex.h>
 ```
 
-*   [Regular Expression](extensios/regex.md)
+*   [Regular Expression](extensions/regex.md)
 
 ---
 
@@ -43,7 +43,7 @@
 #include <kcc/zip.h>
 ```
 
-*   [Zip/Unzip](extensios/zip.md)
+*   [Zip/Unzip](extensions/zip.md)
 
 ---
 
@@ -53,4 +53,4 @@
 #include <kcc/sqlite3.h>
 ```
 
-*   [SQLite3](extensios/sqlite3.md)
+*   [SQLite3](extensions/sqlite3.md)