diff --git a/test/diagnostics/check-unused-diagnostics.swift b/test/diagnostics/check-unused-diagnostics.swift
new file mode 100644
index 0000000000000..b06a522c78b9d
--- /dev/null
+++ b/test/diagnostics/check-unused-diagnostics.swift
@@ -0,0 +1,3 @@
+// REQUIRES: OS=macosx
+
+// RUN: %{python} %utils/check-unused-diagnostics.py
diff --git a/utils/check-unused-diagnostics.py b/utils/check-unused-diagnostics.py
new file mode 100644
index 0000000000000..9c14bfc7c3a57
--- /dev/null
+++ b/utils/check-unused-diagnostics.py
@@ -0,0 +1,94 @@
+import os
+import re
+import sys
+import ahocorasick
+
+def extract_diagnostics_from_file(file_path):
+    """
+    Extract diagnostics patterns from a given file.
+
+    Args:
+    - file_path (str): Path to the file.
+
+    Returns:
+    - list: List of extracted diagnostics with the "diag::" prefix.
+    """
+    with open(file_path, 'r') as file:
+        content = file.read()
+        pattern = r'^\s*(WARNING|NOTE|ERROR|REMARK)\(([^,]+),'
+        return ["diag::" + match.group(2).strip() for match in re.finditer(pattern, content, re.MULTILINE)]
+
+def extract_all_diagnostics():
+    """
+    Recursively extract diagnostics from all diagnostics definition files.
+
+    Returns:
+    - list: List of all extracted diagnostics.
+    """
+    file_pattern = re.compile(r'diagnostic.*\.def$', re.IGNORECASE)
+    identifiers = []
+
+    for dirpath, dirnames, filenames in os.walk('.'):
+        for filename in filenames:
+            if file_pattern.match(filename):
+                file_path = os.path.join(dirpath, filename)
+                identifiers.extend(extract_diagnostics_from_file(file_path))
+
+    return identifiers
+
+def build_automaton(patterns):
+    """
+    Build an Aho-Corasick automaton from the given patterns.
+
+    Args:
+    - patterns (list): List of patterns.
+
+    Returns:
+    - Automaton: Aho-Corasick automaton.
+    """
+    A = ahocorasick.Automaton()
+    for idx, pattern in enumerate(patterns):
+        A.add_word(pattern, (idx, pattern))
+    A.make_automaton()
+    return A
+
+def check_strings_in_files(strings, folder_path):
+    """
+    Check if all strings appear in the files within the given folder (including subfolders).
+
+    Args:
+    - strings (list): List of strings to search for.
+    - folder_path (str): Path to the folder.
+
+    Returns:
+    - list: List of strings that haven't been found.
+    """
+    pattern_map = {s: False for s in strings}
+    automaton = build_automaton(strings)
+
+    for dirpath, dirnames, filenames in os.walk(folder_path):
+        if all(pattern_map.values()):  # End early if all patterns are found
+            break
+        for file_name in filenames:
+            file_path = os.path.join(dirpath, file_name)
+            with open(file_path, 'r', encoding='utf-8', errors='ignore') as f:
+                for _, (_, found) in automaton.iter(f.read()):
+                    pattern_map[found] = True
+
+    return [key for key, found in pattern_map.items() if not found]
+
+def check_for_unused_diagnostics():
+    diagnostics = extract_all_diagnostics()
+    unused_diagnostics = check_strings_in_files(diagnostics, './lib')
+
+    if not unused_diagnostics:
+        print("All diagnostics appear at least once in the codebase!")
+        return 0
+    else:
+        print("The following diagnostics did not appear in the codebase:")
+        for diag in unused_diagnostics:
+            print(diag)
+        return 1
+
+if __name__ == '__main__':
+    sys.exit(check_for_unused_diagnostics())