diff --git a/TeXmacs/progs/check/check-master.scm b/TeXmacs/progs/check/check-master.scm
index 4f8036df79cf3ef7b912a4778e87bfbda31fc1c1..9c17340d858e319f0da461ffcfd6205149c8a08d 100644
--- a/TeXmacs/progs/check/check-master.scm
+++ b/TeXmacs/progs/check/check-master.scm
@@ -94,4 +94,5 @@
   (regtest-tm-define)
   (regtest-tm-dialogue)
   (regtest-fonts)
+  (regtest-tm-tools)
 )
diff --git a/TeXmacs/progs/texmacs/texmacs/tm-tools-test.scm b/TeXmacs/progs/texmacs/texmacs/tm-tools-test.scm
new file mode 100644
index 0000000000000000000000000000000000000000..40567d83b6a2f8a09e4e6305ed17339b05b06a9c
--- /dev/null
+++ b/TeXmacs/progs/texmacs/texmacs/tm-tools-test.scm
@@ -0,0 +1,32 @@
+
+;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
+;;
+;; MODULE      : tm-tools-test.scm
+;; DESCRIPTION : Test suite for tm-tools
+;; COPYRIGHT   : (C) 2023  jingkaimori
+;;
+;; This software falls under the GNU general public license version 3 or later.
+;; It comes WITHOUT ANY WARRANTY WHATSOEVER. For details, see the file LICENSE
+;; in the root directory or <http://www.gnu.org/licenses/gpl-3.0.html>.
+;;
+;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
+
+(texmacs-module (texmacs texmacs tm-tools-test)
+  (:use (texmacs texmacs tm-tools)))
+
+(define (utf8-string-length-test)
+  (regression-test-group
+    "unicode character count" "utf8-string-length-test"
+    utf8-string-length :none
+    (test "empty length" "" 0)
+    (test "ascii length (one byte in utf-8)" "Hello world!" 12)
+    (test "russian length (two byte in utf-8)" "Всем привет!" 12)
+    (test "kanji length (three byte in utf-8)" "你好世界！" 5)
+    (test "fraktur length (four byte in utf-8)" "𝕳𝖊𝖑𝖑𝖔 𝖜𝖔𝖗𝖑𝖉!" 12)
+    (test "hybrid length" "Hello world!Всем привет!你好世界！𝕳𝖊𝖑𝖑𝖔 𝖜𝖔𝖗𝖑𝖉!" 41)))
+
+(tm-define (regtest-tm-tools)
+  (let ((n (+ (utf8-string-length-test)
+              0)))
+    (display* "Total: " (object->string n) " tests.\n")
+    (display "Test suite of tm-tools: ok\n")))
\ No newline at end of file
diff --git a/TeXmacs/progs/texmacs/texmacs/tm-tools.scm b/TeXmacs/progs/texmacs/texmacs/tm-tools.scm
index f7ccec41730e8aafa1c517c3f691772a28935fd5..167d73e36d0edc7e0b654ce9843be5ec49b859e1 100644
--- a/TeXmacs/progs/texmacs/texmacs/tm-tools.scm
+++ b/TeXmacs/progs/texmacs/texmacs/tm-tools.scm
@@ -17,9 +17,22 @@
 ;; Document statistics
 ;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
 
+;; TODO: if string in scheme represent unicode codepoint with single character 
+;;   rather than utf-8 encoding, replace this function with string-length
+(tm-define (utf8-string-length s)
+  (let ((lth-s (string-length s)))
+    (if (== lth-s 0)
+      0
+      (let* ((s-first (char->integer (string-ref s 0)))
+             (s-rest (substring s 1 lth-s))
+             (lth-rest (utf8-string-length s-rest)))
+        (cond
+          ((== (logand s-first #xc0) #x80) lth-rest)
+          (else (+ lth-rest 1)))))))
+
 (tm-define (count-characters doc)
   (with s (convert doc "texmacs-tree" "verbatim-snippet")
-    (string-length s)))
+    (utf8-string-length s)))
 
 (define (compress-spaces s)
   (let* ((s1 (string-replace s "\n" " "))
diff --git a/TeXmacs/tests/17_1.scm b/TeXmacs/tests/17_1.scm
new file mode 100644
index 0000000000000000000000000000000000000000..e5db7ad8a751eb958a0f34cb747c7d26722c86fc
--- /dev/null
+++ b/TeXmacs/tests/17_1.scm
@@ -0,0 +1,12 @@
+(define (test-count-characters)
+  (load-buffer "$TEXMACS_PATH/tests/17_1.tm")
+  (regression-test-group
+   "count-characters" "result"
+   count-characters :none
+   (test "character count" (buffer-tree) 41)))
+
+(tm-define (test_9_1)
+  (let ((n (+ (test-no-title)
+              0)))
+    (display* "Total: " (object->string n) " tests.\n")
+    (display "Test suite of 9_1: ok\n")))
diff --git a/TeXmacs/tests/17_1.tm b/TeXmacs/tests/17_1.tm
new file mode 100644
index 0000000000000000000000000000000000000000..975b4df378e9c23c5cbdc8ee39703ac9fd5b83ce
--- /dev/null
+++ b/TeXmacs/tests/17_1.tm
@@ -0,0 +1,12 @@
+<TeXmacs|2.1.2>
+
+<style|<tuple|generic|chinese>>
+
+<\body>
+  Hello world!\<#412\>\<#441\>\<#435\>\<#43C\>
+  \<#43F\>\<#440\>\<#438\>\<#432\>\<#435\>\<#442\>!\<#4F60\>\<#597D\>\<#4E16\>\<#754C\>\<#FF01\>\<#1D573\>\<#1D58A\>\<#1D591\>\<#1D591\>\<#1D594\>
+  \<#1D59C\>\<#1D594\>\<#1D597\>\<#1D591\>\<#1D589\>!
+</body>
+
+<initial|<\collection>
+</collection>>
\ No newline at end of file