diff --git a/_config.yml b/_config.yml
index bc34ef8..98bebd0 100644
--- a/_config.yml
+++ b/_config.yml
@@ -6,6 +6,7 @@ author: the TCLab Team
 copyright: "2025"
 logo: tclab.png
 exclude_patterns: ["_build", ".venv", "*.ipynb_checkpoints", ".pipenv"]
+only_build_toc_files: true
 
 # Force re-execution of notebooks on each build.
 # See https://jupyterbook.org/content/execute.html
diff --git a/_toc.de.yml b/_toc.de.yml
new file mode 100644
index 0000000..10c676b
--- /dev/null
+++ b/_toc.de.yml
@@ -0,0 +1,15 @@
+# Table of contents
+# Learn more at https://jupyterbook.org/customize/toc.html
+
+format: jb-book
+root: U00_Intro
+chapters:
+- file: U01_DSP_Basics
+- file: U02_Project
+  sections:
+    - file: U02_1_Input
+    - file: U02_2_Freq_Shift
+    - file: U02_3_Low_Pass
+    - file: U02_4_Sync
+    - file: U02_5_Output
+
diff --git a/_toc.yml b/_toc.en.yml
similarity index 59%
rename from _toc.yml
rename to _toc.en.yml
index 656bdd4..92722f0 100644
--- a/_toc.yml
+++ b/_toc.en.yml
@@ -2,22 +2,13 @@
 # Learn more at https://jupyterbook.org/customize/toc.html
 
 format: jb-book
-root: U00_Intro
+root: U00_Intro.en
 chapters:
-- file: U00_Intro.en
-- file: U01_DSP_Basics
 - file: U01_DSP_Basics.en
-- file: U02_Project
 - file: U02_Project.en
   sections:
-    - file: U02_1_Input
     - file: U02_1_Input.en
-    - file: U02_2_Freq_Shift
     - file: U02_2_Freq_Shift.en
-    - file: U02_3_Low_Pass
     - file: U02_3_Low_Pass.en
-    - file: U02_4_Sync
     - file: U02_4_Sync.en
-    - file: U02_5_Output
     - file: U02_5_Output.en
-