diff --git a/core/String.carp b/core/String.carp
index 41a595ae9..3c946b504 100644
--- a/core/String.carp
+++ b/core/String.carp
@@ -50,7 +50,7 @@
   (doc from-chars "Creates a string from an array of characters.")
   (register from-chars (Fn [&(Array Char)] String))
   (doc tail "Returns the tail of a string (all characters except the first).")
-  (register tail (λ [(Ref String)] String))
+  (register tail (Fn [&String] String))
   (doc format "Formats a string.")
   (register format (Fn [&String &String] String))
   (implements format String.format)
@@ -133,15 +133,9 @@
     (from-chars &(Array.suffix &(chars s) b)))
 
   (doc starts-with? "Check if the string `s` begins with the string `sub`.")
-  (defn starts-with? [s sub]
-    (let [ls (length sub)]
-      (and (>= (length s) ls) (= sub &(prefix s ls)))))
-
+  (register starts-with? (Fn [&String &String] Bool))
   (doc ends-with? "Check if the string `s` ends with the string `sub`.")
-  (defn ends-with? [s sub]
-    (let [ls (length s)
-          lsub (length sub)]
-      (and (>= ls lsub) (= sub &(suffix s (- ls lsub))))))
+  (register ends-with? (Fn [&String &String] Bool))
 
   (doc zero "The empty string.")
   (defn zero [] @"")
@@ -240,6 +234,29 @@
   (doc lines "splits a string into lines.")
   (defn lines [s]
     (split-by s &[\newline]))
+
+  (doc copy-map "Maps a function over the UTF-8 characters (`chars`) of a string, returning a new string.")
+  (defn copy-map [f s]
+    (from-chars &(Array.copy-map f &(chars s))))
+
+  (doc copy-filter "Filters the UTF-8 characters (`chars`) of a string using a predicate, returning a new string.")
+  (defn copy-filter [f s]
+    (from-chars &(Array.copy-filter f &(chars s))))
+
+  (doc any? "Checks if any UTF-8 character (`chars`) in a string satisfies a predicate.")
+  (defn any? [f s]
+    (Array.any? f &(chars s)))
+
+  (doc all? "Checks if all UTF-8 characters (`chars`) in a string satisfy a predicate.")
+  (defn all? [f s]
+    (Array.all? f &(chars s)))
+
+  (doc reduce "Reduces a string using its UTF-8 characters (`chars`), a function and an initial value.")
+  (defn reduce [f init s]
+    (Array.reduce f init &(chars s)))
+
+  (doc replace "Replaces all occurrences of a literal substring in a string with another string.")
+  (register replace (Fn [&String &String &String] String))
 )
 
 (defmodule StringCopy
@@ -573,7 +590,6 @@
 )
 
 (defmodule Uint32Extra
-  (doc str "Converts a Uint32 reference to a string.")
   (defn str [a] (Uint32.str @a))
   (implements str Uint32Extra.str)
   (doc prn "Converts a Uint32 reference to a string for printing.")
diff --git a/core/carp_string.h b/core/carp_string.h
index 631fd088e..02c4fafbc 100644
--- a/core/carp_string.h
+++ b/core/carp_string.h
@@ -191,6 +191,20 @@ String String_tail(const String* s) {
     return news;
 }
 
+bool String_starts_MINUS_with_QMARK_(const String* s, const String* sub) {
+    size_t ls = strlen(*s);
+    size_t lsub = strlen(*sub);
+    if (lsub > ls) return false;
+    return memcmp(*s, *sub, lsub) == 0;
+}
+
+bool String_ends_MINUS_with_QMARK_(const String* s, const String* sub) {
+    size_t ls = strlen(*s);
+    size_t lsub = strlen(*sub);
+    if (lsub > ls) return false;
+    return memcmp(*s + (ls - lsub), *sub, lsub) == 0;
+}
+
 String String_empty() {
     String s = CARP_MALLOC(1);
     s[0] = '\0';
@@ -394,6 +408,49 @@ int String_index_MINUS_of_MINUS_string(const String* s, const String* needle) {
     return (int)(result - *s);
 }
 
+String String_replace(const String* s, const String* needle, const String* replacement) {
+    size_t needle_len = strlen(*needle);
+    if (needle_len == 0) {
+        return String_copy(s);
+    }
+
+    size_t s_len = strlen(*s);
+    size_t replacement_len = strlen(*replacement);
+
+    // First pass: count occurrences
+    size_t count = 0;
+    const char* tmp = *s;
+    while ((tmp = strstr(tmp, *needle))) {
+        count++;
+        tmp += needle_len;
+    }
+
+    if (count == 0) {
+        return String_copy(s);
+    }
+
+    // Allocate once
+    size_t new_len = s_len + (count * replacement_len) - (count * needle_len);
+    String result = CARP_MALLOC(new_len + 1);
+    if (result == NULL) return NULL;
+
+    // Second pass: fill the buffer
+    char* insert_ptr = result;
+    const char* current_ptr = *s;
+    while (count--) {
+        const char* next_needle = strstr(current_ptr, *needle);
+        size_t skipped_len = next_needle - current_ptr;
+        memcpy(insert_ptr, current_ptr, skipped_len);
+        insert_ptr += skipped_len;
+        memcpy(insert_ptr, *replacement, replacement_len);
+        insert_ptr += replacement_len;
+        current_ptr = next_needle + needle_len;
+    }
+    strcpy(insert_ptr, current_ptr);
+
+    return result;
+}
+
 String Pointer_strp(void* in) {
     int size = snprintf(NULL, 0, "%p", in) + 1;
     String buffer = CARP_MALLOC(size);
diff --git a/test/string.carp b/test/string.carp
index 47c14ae04..f9f2ddbbb 100644
--- a/test/string.carp
+++ b/test/string.carp
@@ -400,4 +400,69 @@
                 3
                 (Dynamic.length (Dynamic.String.to-array "abc"))
                 "Dynamic.String.to-array works as expected (check length)")
+
+  (assert-equal test
+                "bcde"
+                &(copy-map &(fn [c] (Char.from-int (Int.inc (Char.to-int @c)))) "abcd")
+                "copy-map works as expected")
+  (assert-equal test
+                "bd"
+                &(copy-filter &(fn [c] (or (= @c \b) (= @c \d))) "abcd")
+                "copy-filter works as expected")
+  (assert-true test
+               (any? &(fn [c] (= @c \c)) "abcd")
+               "any? works as expected I")
+  (assert-false test
+                (any? &(fn [c] (= @c \z)) "abcd")
+                "any? works as expected II")
+  (assert-true test
+               (all? &(fn [c] (not (= @c \z))) "abcd")
+               "all? works as expected I")
+  (assert-false test
+                (all? &(fn [c] (= @c \a)) "abcd")
+                "all? works as expected II")
+  (assert-equal test
+                4
+                (reduce &(fn [acc c] (Int.inc acc)) 0 "abcd")
+                "reduce works as expected (counting characters)")
+  (assert-equal test
+                "hEllo world"
+                &(replace "hello world" "e" "E")
+                "replace works as expected I")
+  (assert-equal test
+                "hi there hi"
+                &(replace "hello there hello" "hello" "hi")
+                "replace works as expected II")
+  (assert-equal test
+                "aaaaa"
+                &(replace "aba" "b" "aaa")
+                "replace works as expected III")
+  (assert-equal test
+                "xyz"
+                &(replace "xyz" "" "abc")
+                "replace with empty needle returns original string")
+  (assert-equal test
+                ""
+                &(replace "aaaaa" "a" "")
+                "replace with empty replacement works")
+  (assert-equal test
+                "hello world"
+                &(replace "hello world" "universe" "planet")
+                "replace with non-existent needle returns copy")
+  (assert-equal test
+                "abc"
+                &(replace "xyz" "xyz" "abc")
+                "replace whole string works")
+  (assert-equal test
+                "bba"
+                &(replace "aaaaa" "aa" "b")
+                "replace multiple overlapping-style patterns works (non-overlapping)")
+  (assert-equal test
+                "!!!hello!!!"
+                &(replace "   hello   " "   " "!!!")
+                "replace at start and end works")
+  (assert-equal test
+                "hello 🪐 world"
+                &(replace "hello 🌏 world" "🌏" "🪐")
+                "replace works with multi-byte Unicode characters")
 )