diff --git a/src/klib.c b/src/klib.c
new file mode 100644
index 0000000..e91b81d
--- /dev/null
+++ b/src/klib.c
@@ -0,0 +1,161 @@
+#include "klib.h"
+#include "string.h"
+
+/* ---- character classification -------------------------------------- */
+
+bool isDigit(int c) { return c >= '0' && c <= '9'; }
+bool isUpper(int c) { return c >= 'A' && c <= 'Z'; }
+bool isLower(int c) { return c >= 'a' && c <= 'z'; }
+bool isAlpha(int c) { return isUpper(c) || isLower(c); }
+bool isAlnum(int c) { return isAlpha(c) || isDigit(c); }
+bool isSpace(int c) { return c == ' ' || c == '\t' || c == '\n' || c == '\r' || c == '\v' || c == '\f'; }
+bool isHexDigit(int c) { return isDigit(c) || (c >= 'a' && c <= 'f') || (c >= 'A' && c <= 'F'); }
+
+int toUpper(int c) { return isLower(c) ? c - 'a' + 'A' : c; }
+int toLower(int c) { return isUpper(c) ? c - 'A' + 'a' : c; }
+
+/* ---- string manipulation --------------------------------------------- */
+
+char* strcpy(char* dest, const char* src)
+{
+    char* out = dest;
+    while ((*out++ = *src++) != 0)
+        ;
+    return dest;
+}
+
+char* strncpy(char* dest, const char* src, usize count)
+{
+    usize i = 0;
+    for (; i < count && src[i]; i++)
+        dest[i] = src[i];
+    for (; i < count; i++)
+        dest[i] = 0;
+    return dest;
+}
+
+char* strcat(char* dest, const char* src)
+{
+    strcpy(dest + strlen(dest), src);
+    return dest;
+}
+
+char* strncat(char* dest, const char* src, usize count)
+{
+    char* end = dest + strlen(dest);
+    usize i = 0;
+    for (; i < count && src[i]; i++)
+        end[i] = src[i];
+    end[i] = 0;
+    return dest;
+}
+
+char* strchr(const char* str, int c)
+{
+    for (;; str++) {
+        if (*str == (char)c)
+            return (char*)str;
+        if (*str == 0)
+            return nullptr;
+    }
+}
+
+char* strrchr(const char* str, int c)
+{
+    const char* last = nullptr;
+    for (;; str++) {
+        if (*str == (char)c)
+            last = str;
+        if (*str == 0)
+            return (char*)last;
+    }
+}
+
+char* strstr(const char* haystack, const char* needle)
+{
+    if (!*needle)
+        return (char*)haystack;
+    usize needleLen = strlen(needle);
+    for (; *haystack; haystack++) {
+        if (memcmp(haystack, needle, needleLen) == 0)
+            return (char*)haystack;
+    }
+    return nullptr;
+}
+
+usize strspn(const char* str, const char* accept)
+{
+    usize count = 0;
+    for (; str[count]; count++) {
+        if (!strchr(accept, str[count]))
+            break;
+    }
+    return count;
+}
+
+usize strcspn(const char* str, const char* reject)
+{
+    usize count = 0;
+    for (; str[count]; count++) {
+        if (strchr(reject, str[count]))
+            break;
+    }
+    return count;
+}
+
+char* strTokR(char* str, const char* delim, char** savePtr)
+{
+    char* cursor = str ? str : *savePtr;
+    if (cursor == nullptr)
+        return nullptr;
+
+    cursor += strspn(cursor, delim);
+    if (*cursor == 0) {
+        *savePtr = nullptr;
+        return nullptr;
+    }
+
+    char* tokenEnd = cursor + strcspn(cursor, delim);
+    if (*tokenEnd) {
+        *tokenEnd = 0;
+        *savePtr = tokenEnd + 1;
+    } else {
+        *savePtr = nullptr;
+    }
+    return cursor;
+}
+
+/* ---- number parsing ---------------------------------------------------- */
+
+static int digitValue(int c)
+{
+    if (c >= '0' && c <= '9')
+        return c - '0';
+    if (c >= 'a' && c <= 'z')
+        return c - 'a' + 10;
+    if (c >= 'A' && c <= 'Z')
+        return c - 'A' + 10;
+    return -1;
+}
+
+uint64 strtoul(const char* str, char** endPtr, int base)
+{
+    const char* cursor = str;
+    while (isSpace((unsigned char)*cursor))
+        cursor++;
+
+    bool negative = false;
+    if (*cursor == '+' || *cursor == '-') {
+        negative = (*cursor == '-');
+        cursor++;
+    }
+
+    if ((base == 0 || base == 16) && cursor[0] == '0' && (cursor[1] == 'x' || cursor[1] == 'X')) {
+        cursor += 2;
+        base = 16;
+    } else if (base == 0 && cursor[0] == '0') {
+        base = 8;
+    } else if (base == 0) {
+        base = 10;
+    }
+