diff --git a/link-peps.py b/link-peps.py
new file mode 100755
index 0000000..03765ab
--- /dev/null
+++ b/link-peps.py
@@ -0,0 +1,51 @@
+#! /usr/bin/env python
+"""Destructively* link PEPs in the given Markdown document.
+
+"PEP nnnn" or "PEP nnnn (title)" are converted to "[PEP nnnn](url) (title)".
+
+* The document is changed "destructively". Make a backup (e.g. `git add`)
+  before runnig the tool.
+
+This is just a simple helper for simple cases. Always check its work.
+"""
+
+import re
+import fileinput
+import urllib.request
+import json
+
+PEP_RE = re.compile(
+    r'''
+        (?<!\[)          # Don't process links (square bracket before 'PEP')
+        PEP              # 'PEP'
+        (\s|-)*          # Whitespace or dash(es)
+        (?P<num>\d+)     # PEP number
+        \s*              # Optional whitespace
+        (                # Optionally:
+          \(             #  parenthesized
+            (?P<title>   #   title
+              [^)]+      #    (anything except end-parenthesis)
+            )
+          \)
+        )?
+    ''',
+    re.VERBOSE,
+)
+
+def linkify(match):
+    number = int(match['num'])
+    title = match['title'] or get_title(number)
+    return f'[PEP {number}](https://peps.python.org/pep-{number:04}/) ({title})'
+
+def get_title(number):
+    global pep_info
+    try:
+        pep_info
+    except NameError:
+        with urllib.request.urlopen('https://peps.python.org/api/peps.json') as response:
+            pep_info = json.load(response)
+    return pep_info[str(number)]['title']
+
+
+for line in fileinput.input(inplace=True):
+    print(PEP_RE.sub(linkify, line.rstrip()))