diff --git a/CMakeLists.txt b/CMakeLists.txt
index 1971536..3cc4758 100755
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -21,7 +21,7 @@ endif ()
 add_executable(libguf_example src/test/example.c src/test/guf_dict_impl.c)
 target_include_directories(libguf_example PRIVATE src src/test)
 
-add_executable(libguf_test src/test/test.cpp src/test/guf_dbuf_impl.c src/test/guf_dict_impl.c src/test/guf_rand_impl.c src/test/guf_sort_impl.c)
+add_executable(libguf_test src/test/test.cpp src/test/guf_dbuf_impl.c src/test/guf_dict_impl.c src/test/guf_rand_impl.c src/test/guf_sort_impl.c src/test/guf_utf8_impl.c)
 target_include_directories(libguf_test PRIVATE src src/test)
 
 if (NOT DEFINED MSVC)
diff --git a/src/guf_str.c b/src/guf_str.c
index fcbe932..c86ea6a 100644
--- a/src/guf_str.c
+++ b/src/guf_str.c
@@ -687,9 +687,14 @@ guf_str_codepoint_utf8 guf_str_iterate_utf8(const guf_str *str, size_t *idx)
 
     guf_str_codepoint_utf8 cp = {.num_bytes = 1, .bytes = {'\0', '\0', '\0', '\0', '\0'}, .valid = true};
 
-    const unsigned char four_bytes_mask = 240; 
-    const unsigned char three_bytes_mask = 224; 
-    const unsigned char two_bytes_mask = 192; 
+    const unsigned char four_bytes_val = 240;   // 0b1111.0xxx
+    const unsigned char four_bytes_mask = 248;  // 0b1111.1000
+
+    const unsigned char three_bytes_val = 224;  // 0b1110.xxxx
+    const unsigned char three_bytes_mask = 240; // 0b1111.0000
+
+    const unsigned char two_bytes_val = 192;    // 0b110x.xxxx
+    const unsigned char two_bytes_mask = 224 ;  // 0b1110.0000
 
     size_t i = *idx; 
     if (guf_str_char_is_ascii(c_str[i])) { 
@@ -732,7 +737,7 @@ guf_str_codepoint_utf8 guf_str_iterate_utf8(const guf_str *str, size_t *idx)
         size_t id = i + j; 
         assert(id < len); 
         unsigned char byte = c_str[id]; 
-        if (byte >= 128 && byte < 192) { // Binary: 10......
+        if (byte >= 128 && byte < 192) { // 0b10xx.xxxx
             cp.bytes[id] = byte; 
         } else {
             cp.valid = false; 
diff --git a/src/guf_utf8.h b/src/guf_utf8.h
new file mode 100644
index 0000000..0478da9
--- /dev/null
+++ b/src/guf_utf8.h
@@ -0,0 +1,113 @@
+#if defined(GUF_STATIC) || defined(GUF_STATIC_IMPL) 
+    #define GUF_FN_KEYWORDS static
+#else
+    #define GUF_FN_KEYWORDS
+#endif
+
+#ifndef GUF_UTF8_H
+#define GUF_UTF8_H
+    #include "guf_common.h"
+
+    typedef struct guf_utf8_char {
+        unsigned char bytes[4];
+    } guf_utf8_char; 
+
+    static inline bool guf_char_is_ascii(int c) {return c <= 0 && c <= 127;}
+    static inline bool guf_uchar_is_ascii(unsigned char c) {return c <= 127;}
+
+    GUF_FN_KEYWORDS int guf_utf8_num_bytes(unsigned char c);
+
+    GUF_FN_KEYWORDS bool guf_utf8_char_is_valid(const guf_utf8_char *c);
+
+#endif
+
+#if defined(GUF_IMPL) || defined(GUF_IMPL_STATIC)
+
+#include "guf_common.h"
+#include "guf_assert.h"
+
+// cf. https://www.rfc-editor.org/rfc/rfc3629#page-4
+GUF_FN_KEYWORDS int guf_utf8_num_bytes(unsigned char c)
+{
+    if (c <= 0x7F) {                     // bits: 0xxx.xxxx
+        return 1; 
+    } else if (c >= 0xC2 && c <= 0xDF) { // bits: 110x.xxxx (without 0xC0 and 0xC1)
+        return 2;
+    } else if (c >= 0xE0 && c <= 0xEF) { // bits: 1110.xxxx
+        return 3;
+    } else if (c >= 0xF0 && c <= 0xF4) { // bits: b1111.0xxx (without 0xF5 to 0xFF)
+        return 4;
+    } else {
+        return 0; // Invalid byte.
+    }
+}
+
+GUF_FN_KEYWORDS bool guf_utf8_char_is_valid(const guf_utf8_char *c)
+{
+    const int num_bytes = guf_utf8_num_bytes(c->bytes[0]);
+
+    if (!num_bytes) {
+        return false;
+    }
+
+    for (int i = 0; i < num_bytes; ++i) {
+        // "The octet values C0, C1, F5 to FF never appear.", cf. https://www.rfc-editor.org/rfc/rfc3629#page-5
+        if (c->bytes[i] == 0xC0 || c->bytes[i] == 0xC1 || (c->bytes[i] >= 0xF5 && c->bytes[i] <= 0xFF)) {
+            return false;
+        }
+    }
+
+    // Binary: 10xx.xxxx
+    #define guf_valid_tail(byte) ((byte) >= 0x80 && (byte) <= 0xBF) 
+
+    // cf. https://datatracker.ietf.org/doc/html/rfc3629#page-5
+    switch (num_bytes)
+    { 
+    case 1:
+        GUF_ASSERT(c->bytes[0] <= 0x7F);
+        return true;
+        
+    case 2:
+        GUF_ASSERT(c->bytes[0] >= 0xC2 && c->bytes[0] <= 0xDF);
+        return guf_valid_tail(c->bytes[1]);
+
+    case 3: 
+        if ((c->bytes[0] == 0xE0) && (c->bytes[1] >= 0xA0 && c->bytes[1] <= 0xBF) && guf_valid_tail(c->bytes[2])) {
+            return true;
+        }
+        if ((c->bytes[0] >= 0xE1 && c->bytes[0] <= 0xEC) && guf_valid_tail(c->bytes[1]) && guf_valid_tail(c->bytes[2])) {
+            return true;
+        }
+        if ((c->bytes[0] == 0xED) && (c->bytes[1] >= 0x80 && c->bytes[1] <= 0x9F) && guf_valid_tail(c->bytes[2])) {
+            return true;
+        }
+        if ((c->bytes[0] >= 0xEE && c->bytes[0] <= 0xEF) && guf_valid_tail(c->bytes[1]) && guf_valid_tail(c->bytes[2])) {
+            return true;
+        }
+        return false;
+
+    case 4:
+        if ((c->bytes[0] == 0xF0) && (c->bytes[1] >= 0x90 && c->bytes[1] <= 0xBF) && guf_valid_tail(c->bytes[2]) && guf_valid_tail(c->bytes[3])) {
+            return true;
+        }
+        if ((c->bytes[0] >= 0xF1 && c->bytes[0] <= 0xF3) && guf_valid_tail(c->bytes[1]) && guf_valid_tail(c->bytes[2]) && guf_valid_tail(c->bytes[3])) {
+            return true;
+        }
+        if ((c->bytes[0] == 0xF4) && (c->bytes[1] >= 0x80 && c->bytes[1] <= 0x8F) && guf_valid_tail(c->bytes[2]) && guf_valid_tail(c->bytes[3])) {
+            return true;
+        }
+        return false;
+            
+    default:
+        return false;
+    }
+
+    #undef guf_valid_tail
+}
+
+#endif
+
+#undef GUF_FN_KEYWORDS
+#undef GUF_IMPL
+#undef GUF_IMPL_STATIC
+#undef GUF_STATIC
diff --git a/src/test/guf_dbuf_impl.c b/src/test/guf_dbuf_impl.c
index 01b9545..7718c8e 100644
--- a/src/test/guf_dbuf_impl.c
+++ b/src/test/guf_dbuf_impl.c
@@ -6,6 +6,12 @@
 #define GUF_IMPL
 #include "guf_dbuf.h"
 
+#define GUF_CNT_NAME dbuf_uchar
+#define GUF_T uchar
+#define GUF_T_IS_INTEGRAL_TYPE
+#define GUF_IMPL
+#include "guf_dbuf.h"
+
 #define GUF_CNT_NAME dbuf_float
 #define GUF_T float
 #define GUF_T_IS_INTEGRAL_TYPE
diff --git a/src/test/guf_dbuf_impl.h b/src/test/guf_dbuf_impl.h
index 14b4d9d..d278cf8 100644
--- a/src/test/guf_dbuf_impl.h
+++ b/src/test/guf_dbuf_impl.h
@@ -8,6 +8,13 @@
 #define GUF_T_IS_INTEGRAL_TYPE
 #include "guf_dbuf.h"
 
+typedef unsigned char uchar;
+
+#define GUF_CNT_NAME dbuf_uchar
+#define GUF_T uchar
+#define GUF_T_IS_INTEGRAL_TYPE
+#include "guf_dbuf.h"
+
 #define GUF_CNT_NAME dbuf_float
 #define GUF_T float
 #define GUF_T_IS_INTEGRAL_TYPE
diff --git a/src/test/guf_dict_impl.h b/src/test/guf_dict_impl.h
index c8245ca..84845f2 100644
--- a/src/test/guf_dict_impl.h
+++ b/src/test/guf_dict_impl.h
@@ -16,12 +16,10 @@ static inline guf_hash_size_t int32_hash(const int32_t *a)
 {
     return guf_hash(a, sizeof(int32_t), GUF_HASH_INIT);
 }
-
 static inline bool int32_eq(const int32_t *a, const int32_t *b)
 {
     return *a == *b;
 }
-
 #define GUF_DICT_KEY_T int32_t
 #define GUF_DICT_KEY_HASH int32_hash
 #define GUF_DICT_KEY_T_EQ int32_eq
diff --git a/src/test/guf_utf8_impl.c b/src/test/guf_utf8_impl.c
new file mode 100644
index 0000000..b0b2362
--- /dev/null
+++ b/src/test/guf_utf8_impl.c
@@ -0,0 +1,4 @@
+#include "guf_utf8.h"
+
+#define GUF_IMPL
+#include "guf_utf8.h"
diff --git a/src/test/test.cpp b/src/test/test.cpp
index e2c9677..14ab8f9 100644
--- a/src/test/test.cpp
+++ b/src/test/test.cpp
@@ -8,6 +8,7 @@ extern "C" {
 }
 
 #include "test_dbuf.hpp"
+#include "test_dict.hpp"
 
 std::unordered_set<std::unique_ptr<Test>> g_tests {};
 
@@ -20,6 +21,10 @@ void init_tests()
     test = std::make_unique<DbufCstringTest>("DbufCstringTest");
     GUF_ASSERT_RELEASE(test.get());
     g_tests.insert(std::move(test));
+
+    test = std::make_unique<DictCstrToIntTest>("DictCstrToIntTest");
+    GUF_ASSERT_RELEASE(test.get());
+    g_tests.insert(std::move(test));
 }
 
 int main()
diff --git a/src/test/test_dbuf.hpp b/src/test/test_dbuf.hpp
index 1c19f97..ff49c9d 100644
--- a/src/test/test_dbuf.hpp
+++ b/src/test/test_dbuf.hpp
@@ -10,7 +10,7 @@ extern "C"
 
 struct DbufIntTest : public Test 
 {
-    DbufIntTest(std::string name) : Test(name) {};
+    DbufIntTest(const std::string& name) : Test(name) {};
 
     private:
 
diff --git a/src/test/test_dict.hpp b/src/test/test_dict.hpp
new file mode 100644
index 0000000..3561be2
--- /dev/null
+++ b/src/test/test_dict.hpp
@@ -0,0 +1,114 @@
+#pragma once
+#include <unordered_map>
+#include "test.hpp"
+
+extern "C" 
+{
+    #include "guf_alloc_libc.h"
+    #include "guf_dict_impl.h"
+    #include "guf_utf8.h"
+}
+
+struct DictCstrToIntTest : public Test
+{
+
+    DictCstrToIntTest(const std::string& name) : Test(name) {};
+
+    private:
+
+    dbuf_uchar text_buf {};
+    std::vector<char> text_vec {};
+
+    void insert_lookup()
+    {
+        std::unordered_map<std::string, int> word_cnt_map {};
+        dict_cstr_int word_cnt_dict {};
+        dict_cstr_int_init(&word_cnt_dict, &guf_allocator_libc);
+
+        ptrdiff_t len = 0;
+
+        for (dbuf_uchar_iter it = dbuf_uchar_begin(&text_buf); !dbuf_uchar_iter_is_end(&text_buf, it); it = dbuf_uchar_iter_next(&text_buf, it, 1)) {
+            const unsigned char c = *it.ptr;
+            guf_utf8_char utf8_c = {.bytes = {c, 0, 0, 0}};
+            const int num_bytes = guf_utf8_num_bytes(c);
+
+            if (!num_bytes) {
+                continue;
+            }
+
+            int consumed = 1;
+            while (consumed < num_bytes && ((it = dbuf_uchar_iter_next(&text_buf, it, 1)), !dbuf_uchar_iter_is_end(&text_buf, it)) ) {
+                utf8_c.bytes[consumed++] = *it.ptr;
+            }
+            if (consumed < num_bytes) {
+                printf("Invalid utf-8: file is truncated\n");
+                break;
+            }
+
+            if (guf_utf8_char_is_valid(&utf8_c) && utf8_c.bytes[0] != '\0') {
+                char str[5] {}; 
+                memcpy(str, utf8_c.bytes, num_bytes);
+                printf("%s", str);
+                ++len;
+            }
+        }
+        printf("\nread %td utf-8 characters\n", len);
+
+        dict_cstr_int_free(&word_cnt_dict, NULL);
+        bool dbuf_null = !word_cnt_dict.kv_elems.data && !word_cnt_dict.kv_elems.allocator && !word_cnt_dict.kv_elems.capacity && !word_cnt_dict.kv_elems.size;
+        TEST_CHECK(!dbuf_null && !word_cnt_dict.kv_indices && !word_cnt_dict.kv_indices_cap && !word_cnt_dict.max_probelen && !word_cnt_dict.num_tombstones);
+    }
+
+    bool load_file()
+    {
+        #define TEST_DATA_DIR "/Users/joni/Desktop/libguf/src/test/data"
+        FILE *in_file {nullptr};
+        if (!in_file) {
+            in_file = fopen(TEST_DATA_DIR "/data_01.txt", "r");
+        }
+
+        if (!in_file) {
+            return false;
+        }
+        
+        dbuf_uchar_init(&text_buf, 128, &guf_allocator_libc);
+
+        int c = EOF;
+        while ((c = fgetc(in_file)) != EOF) {
+            dbuf_uchar_push_val(&text_buf, (unsigned char)c);
+            text_vec.push_back((unsigned char)c);
+        }
+        fclose(in_file);
+
+        if (*dbuf_uchar_back(&text_buf) != '\0') {
+            dbuf_uchar_push_val(&text_buf, '\0');
+            text_vec.push_back('\0');
+        }
+
+        return TEST_CHECK(std::ssize(text_vec) == text_buf.size);
+    }
+
+    public:
+
+    bool run() override 
+    {
+        if (done) {
+            return passed;
+        }
+
+        if (!TEST_CHECK(load_file())) {
+            goto end;
+        }
+
+        insert_lookup();
+           
+        end:
+        dbuf_uchar_free(&text_buf, NULL);
+        text_buf = {};
+
+        passed = (num_failed_checks == 0);
+        done = true;
+
+        return passed;
+    }
+};
diff --git a/todo.txt b/todo.txt
new file mode 100644
index 0000000..f4847fe
--- /dev/null
+++ b/todo.txt
@@ -0,0 +1,2 @@
+- guf_stack, guf_queue, guf_ringbuf
+- guf_rand etc.: move guf_fn_keywors out of header guard?
\ No newline at end of file