diff --git a/day01.py b/day01.py
index 83b125d..8d8cb39 100644
--- a/day01.py
+++ b/day01.py
@@ -1,5 +1,7 @@
 #!/usr/bin/env python
 
+# https://adventofcode.com/2025/day/1
+
 f = open("day01input.txt", "r")
 a = f.readlines()
 b = list(map(str.strip, a))
diff --git a/day02.py b/day02.py
index 61bb15d..a3a9d1b 100644
--- a/day02.py
+++ b/day02.py
@@ -1,5 +1,7 @@
 #!/usr/bin/env python
 
+https://adventofcode.com/2025/day/2
+
 import re
 from functools import reduce
 
diff --git a/day03.py b/day03.py
index e8bd2d5..9bc5da3 100644
--- a/day03.py
+++ b/day03.py
@@ -1,5 +1,7 @@
 #!/usr/bin/env python
 
+https://adventofcode.com/2025/day/3
+
 f = open("day03input.txt", "r")
 #f = open("testinput.txt", "r")
 d = [l.strip() for l in f.readlines()]
diff --git a/day04.py b/day04.py
index be8c282..e84aef9 100644
--- a/day04.py
+++ b/day04.py
@@ -1,5 +1,7 @@
 #!/usr/bin/env python
 
+https://adventofcode.com/2025/day/4
+
 f = open("day04input.txt", "r")
 #f = open("testinput.txt", "r")
 d = [l.strip() for l in f.readlines()]