diff --git a/linkcheck/strformat.py b/linkcheck/strformat.py
index fa12f610..923cba7d 100644
--- a/linkcheck/strformat.py
+++ b/linkcheck/strformat.py
@@ -24,9 +24,7 @@ necessarily optimised for large strings, so use with care.
 
 import re
 import textwrap
-import codecs
 import os
-import math
 import time
 import urllib.parse
 import locale
@@ -72,23 +70,6 @@ def ascii_safe(s):
     return s
 
 
-def is_ascii(s):
-    """Test if a string can be encoded in ASCII."""
-    try:
-        s.encode('ascii', 'strict')
-        return True
-    except (UnicodeEncodeError, UnicodeDecodeError):
-        return False
-
-
-def is_encoding(text):
-    """Check if string is a valid encoding."""
-    try:
-        return codecs.lookup(text)
-    except (LookupError, ValueError):
-        return False
-
-
 def url_unicode_split(url):
     """Like urllib.parse.urlsplit(), but always returning unicode parts."""
     return [unicode_safe(s) for s in urllib.parse.urlsplit(url)]
@@ -152,37 +133,11 @@ def indent(text, indent_string="  "):
     return os.linesep.join("%s%s" % (indent_string, x) for x in text.splitlines())
 
 
-def get_line_number(s, index):
-    r"""Return the line number of s[index] or zero on errors.
-    Lines are assumed to be separated by the ASCII character '\n'."""
-    i = 0
-    if index < 0:
-        return 0
-    line = 1
-    while i < index:
-        if s[i] == '\n':
-            line += 1
-        i += 1
-    return line
-
-
 def paginate(text):
     """Print text in pages of lines."""
     pydoc.pager(text)
 
 
-_markup_re = re.compile("<.*?>", re.DOTALL)
-
-
-def remove_markup(s):
-    """Remove all <*> html markup tags from s."""
-    mo = _markup_re.search(s)
-    while mo:
-        s = s[0:mo.start()] + s[mo.end():]
-        mo = _markup_re.search(s)
-    return s
-
-
 def strsize(b, grouping=True):
     """Return human representation of bytes b. A negative number of bytes
     raises a value error."""
@@ -216,32 +171,6 @@ def strtime(t, func=time.localtime):
     return time.strftime("%Y-%m-%d %H:%M:%S", func(t)) + strtimezone()
 
 
-# from quodlibet
-def strduration(duration):
-    """Turn a time value in seconds into hh:mm:ss or mm:ss."""
-    if duration < 0:
-        duration = abs(duration)
-        prefix = "-"
-    else:
-        prefix = ""
-    duration = math.ceil(duration)
-    if duration >= SECONDS_PER_HOUR:  # 1 hour
-        # time, in hours:minutes:seconds
-        return "%s%02d:%02d:%02d" % (
-            prefix,
-            duration // SECONDS_PER_HOUR,
-            (duration % SECONDS_PER_HOUR) // SECONDS_PER_MINUTE,
-            duration % SECONDS_PER_MINUTE,
-        )
-    else:
-        # time, in minutes:seconds
-        return "%s%02d:%02d" % (
-            prefix,
-            duration // SECONDS_PER_MINUTE,
-            duration % SECONDS_PER_MINUTE,
-        )
-
-
 # from quodlibet
 def strduration_long(duration, do_translate=True):
     """Turn a time value in seconds into x hours, x minutes, etc."""
diff --git a/tests/test_strformat.py b/tests/test_strformat.py
index f17029d4..d1c7d1a5 100644
--- a/tests/test_strformat.py
+++ b/tests/test_strformat.py
@@ -72,13 +72,6 @@ class TestStrFormat(unittest.TestCase):
         self.assertEqual(wrap(None, 10), None)
         self.assertFalse(linkcheck.strformat.get_paragraphs(None))
 
-    def test_remove_markup(self):
-        # Test markup removing.
-        self.assertEqual(linkcheck.strformat.remove_markup("<a>"), "")
-        self.assertEqual(linkcheck.strformat.remove_markup("<>"), "")
-        self.assertEqual(linkcheck.strformat.remove_markup("<<>"), "")
-        self.assertEqual(linkcheck.strformat.remove_markup("a < b"), "a < b")
-
     def test_strsize(self):
         # Test byte size strings.
         self.assertRaises(ValueError, linkcheck.strformat.strsize, -1)
@@ -93,10 +86,6 @@ class TestStrFormat(unittest.TestCase):
         self.assertEqual(linkcheck.strformat.strsize(1024 * 1024 * 1024), "1.00GB")
         self.assertEqual(linkcheck.strformat.strsize(1024 * 1024 * 1024 * 14), "14.0GB")
 
-    def test_is_ascii(self):
-        self.assertTrue(linkcheck.strformat.is_ascii("abcd./"))
-        self.assertTrue(not linkcheck.strformat.is_ascii("ä"))
-
     def test_indent(self):
         s = "bla"
         self.assertEqual(linkcheck.strformat.indent(s, ""), s)
@@ -120,18 +109,6 @@ class TestStrFormat(unittest.TestCase):
         t = linkcheck.strformat.strtime(0, func=time.gmtime)
         self.assertEqual(t, "1970-01-01 00:00:00" + zone)
 
-    def test_duration(self):
-        duration = linkcheck.strformat.strduration
-        self.assertEqual(duration(-0.5), "-00:01")
-        self.assertEqual(duration(0), "00:00")
-        self.assertEqual(duration(0.9), "00:01")
-        self.assertEqual(duration(1), "00:01")
-        self.assertEqual(duration(2), "00:02")
-        self.assertEqual(duration(60), "01:00")
-        self.assertEqual(duration(120), "02:00")
-        self.assertEqual(duration(60 * 60), "01:00:00")
-        self.assertEqual(duration(60 * 60 * 24), "24:00:00")
-
     def test_duration_long(self):
         def duration(s):
             return linkcheck.strformat.strduration_long(s, do_translate=False)
@@ -149,17 +126,6 @@ class TestStrFormat(unittest.TestCase):
             duration(60 * 60 * 24 * 365 + 60 * 60 * 24 + 2), "1 year, 1 day"
         )
 
-    def test_linenumber(self):
-        get_line_number = linkcheck.strformat.get_line_number
-        self.assertEqual(get_line_number("a", -5), 0)
-        self.assertEqual(get_line_number("a", 0), 1)
-        self.assertEqual(get_line_number("a\nb", 2), 2)
-
-    def test_encoding(self):
-        is_encoding = linkcheck.strformat.is_encoding
-        self.assertTrue(is_encoding("ascii"))
-        self.assertFalse(is_encoding("hulla"))
-
     def test_unicode_safe(self):
         unicode_safe = linkcheck.strformat.unicode_safe
         self.assertEqual(unicode_safe("a"), "a")