diff --git a/linkcheck/better_exchook2.py b/linkcheck/better_exchook2.py
index cd5cc4f1..f4a5dee6 100644
--- a/linkcheck/better_exchook2.py
+++ b/linkcheck/better_exchook2.py
@@ -232,7 +232,7 @@ def better_exchook(etype, value, tb, out=sys.stdout):
         if value is None or not valuestr:
             line = "%s" % etype
         else:
-            line = "%s: %s" % (etype, valuestr)
+            line = f"{etype}: {valuestr}"
         return line
     if (isinstance(etype, BaseException) or
         (hasattr(types, "InstanceType") and isinstance(etype, types.InstanceType)) or
diff --git a/linkcheck/checker/__init__.py b/linkcheck/checker/__init__.py
index dd0a28f5..e8b2f6de 100644
--- a/linkcheck/checker/__init__.py
+++ b/linkcheck/checker/__init__.py
@@ -197,7 +197,7 @@ def get_index_html(urls):
         except KeyError:
             # Some unicode entries raise KeyError.
             url = name
-        lines.append('<a href="%s">%s</a>' % (url, name))
+        lines.append(f'<a href="{url}">{name}</a>')
     lines.extend(["</body>", "</html>"])
     return os.linesep.join(lines)
 
diff --git a/linkcheck/checker/mailtourl.py b/linkcheck/checker/mailtourl.py
index 536f0baa..04842c6b 100644
--- a/linkcheck/checker/mailtourl.py
+++ b/linkcheck/checker/mailtourl.py
@@ -370,7 +370,7 @@ class MailtoUrl(urlbase.UrlBase):
         The cache url is a comma separated list of emails.
         """
         emails = ",".join(sorted(self.addresses))
-        self.cache_url = "%s:%s" % (self.scheme, emails)
+        self.cache_url = f"{self.scheme}:{emails}"
 
     def can_get_content(self):
         """
diff --git a/linkcheck/checker/unknownurl.py b/linkcheck/checker/unknownurl.py
index 44422a49..f4e5a34d 100644
--- a/linkcheck/checker/unknownurl.py
+++ b/linkcheck/checker/unknownurl.py
@@ -423,7 +423,7 @@ ignored_schemes_other = r"""
 |whatsapp   # WhatsApp
 """
 
-ignored_schemes = "^(%s%s%s%s)$" % (
+ignored_schemes = "^({}{}{}{})$".format(
     ignored_schemes_permanent,
     ignored_schemes_provisional,
     ignored_schemes_historical,
diff --git a/linkcheck/checker/urlbase.py b/linkcheck/checker/urlbase.py
index 969ba972..bf448fcd 100644
--- a/linkcheck/checker/urlbase.py
+++ b/linkcheck/checker/urlbase.py
@@ -508,7 +508,7 @@ class UrlBase:
         else:
             host = "%s:%d" % (self.host, self.port)
         if self.userinfo:
-            urlparts[1] = "%s@%s" % (self.userinfo, host)
+            urlparts[1] = f"{self.userinfo}@{host}"
         else:
             urlparts[1] = host
         # save anchor for later checking
diff --git a/linkcheck/command/arg_parser.py b/linkcheck/command/arg_parser.py
index 0f1fa291..1e8c346a 100644
--- a/linkcheck/command/arg_parser.py
+++ b/linkcheck/command/arg_parser.py
@@ -180,7 +180,7 @@ file entry:
     )
     + "\n".join(
         [
-            " o %s - %s" % (tag, desc)
+            f" o {tag} - {desc}"
             for tag, desc in sorted(checker.const.Warnings.items())
         ]
     )
diff --git a/linkcheck/configuration/__init__.py b/linkcheck/configuration/__init__.py
index 9892da0d..f940c5ba 100644
--- a/linkcheck/configuration/__init__.py
+++ b/linkcheck/configuration/__init__.py
@@ -46,7 +46,7 @@ HtmlCopyright = (
 HtmlAppInfo = App + ", " + HtmlCopyright
 Url = _release.__url__
 SupportUrl = _release.__support_url__
-UserAgent = "Mozilla/5.0 (compatible; %s/%s; +%s)" % (AppName, Version, Url)
+UserAgent = f"Mozilla/5.0 (compatible; {AppName}/{Version}; +{Url})"
 Freeware = (
     AppName
     + """ comes with ABSOLUTELY NO WARRANTY!
@@ -87,7 +87,7 @@ def get_modules_info():
         if version_attr and hasattr(mod, version_attr):
             attr = getattr(mod, version_attr)
             version = attr() if callable(attr) else attr
-            module_infos.append("%s %s" % (name, version))
+            module_infos.append(f"{name} {version}")
         else:
             # ignore attribute errors in case library developers
             # change the version information attribute
diff --git a/linkcheck/configuration/confparse.py b/linkcheck/configuration/confparse.py
index 2d64c75a..544dce3e 100644
--- a/linkcheck/configuration/confparse.py
+++ b/linkcheck/configuration/confparse.py
@@ -227,7 +227,7 @@ class LCConfigParser(RawConfigParser):
                     self.config.add_auth(
                         pattern=auth[0], user=auth[1], password=auth[2]
                     )
-                    password_fields.append("entry/%s/%s" % (auth[0], auth[1]))
+                    password_fields.append(f"entry/{auth[0]}/{auth[1]}")
                 elif len(auth) == 2:
                     self.config.add_auth(pattern=auth[0], user=auth[1])
                 else:
diff --git a/linkcheck/director/console.py b/linkcheck/director/console.py
index e2bc6e06..761b7fab 100644
--- a/linkcheck/director/console.py
+++ b/linkcheck/director/console.py
@@ -53,7 +53,7 @@ class StatusLogger:
 
     def writeln(self, msg):
         """Write status message and line break to file descriptor."""
-        self.fd.write("%s%s" % (msg, os.linesep))
+        self.fd.write(f"{msg}{os.linesep}")
 
     def flush(self):
         """Flush file descriptor."""
diff --git a/linkcheck/htmlutil/loginformsearch.py b/linkcheck/htmlutil/loginformsearch.py
index 77103414..238994e7 100644
--- a/linkcheck/htmlutil/loginformsearch.py
+++ b/linkcheck/htmlutil/loginformsearch.py
@@ -34,7 +34,7 @@ class Form:
 
     def __repr__(self):
         """Return string displaying URL and form data."""
-        return "<url=%s data=%s>" % (self.url, self.data)
+        return f"<url={self.url} data={self.data}>"
 
 
 def search_form(content, cgiuser, cgipassword):
diff --git a/linkcheck/loader.py b/linkcheck/loader.py
index ecf5853e..25e94879 100644
--- a/linkcheck/loader.py
+++ b/linkcheck/loader.py
@@ -34,7 +34,7 @@ def get_package_modules(packagename, packagepath):
     for mod in pkgutil.iter_modules(packagepath):
         if not mod.ispkg:
             try:
-                name = "..%s.%s" % (packagename, mod.name)
+                name = f"..{packagename}.{mod.name}"
                 yield importlib.import_module(name, __name__)
             except ImportError as msg:
                 print(_("WARN: could not load module %s: %s") % (mod.name, msg))
diff --git a/linkcheck/logger/__init__.py b/linkcheck/logger/__init__.py
index 4d5c4c43..f69ab088 100644
--- a/linkcheck/logger/__init__.py
+++ b/linkcheck/logger/__init__.py
@@ -325,7 +325,7 @@ class _Logger(abc.ABC):
         """
         Write string to output descriptor plus a newline.
         """
-        self.write("%s%s" % (s, os.linesep), **args)
+        self.write(f"{s}{os.linesep}", **args)
 
     def has_part(self, name):
         """
diff --git a/linkcheck/logger/dot.py b/linkcheck/logger/dot.py
index fb17d0a1..52db5472 100644
--- a/linkcheck/logger/dot.py
+++ b/linkcheck/logger/dot.py
@@ -70,7 +70,7 @@ class DOTLogger(_GraphLogger):
         """Write edge from parent to node."""
         source = dotquote(self.nodes[node["parent_url"]]["label"])
         target = dotquote(node["label"])
-        self.writeln('  "%s" -> "%s" [' % (source, target))
+        self.writeln(f'  "{source}" -> "{target}" [')
         self.writeln('    label="%s",' % dotquote(node["edge"]))
         if self.has_part("result"):
             self.writeln("    valid=%d," % node["valid"])
diff --git a/linkcheck/logger/xmllog.py b/linkcheck/logger/xmllog.py
index 33338d0a..995acb8c 100644
--- a/linkcheck/logger/xmllog.py
+++ b/linkcheck/logger/xmllog.py
@@ -113,4 +113,4 @@ class _XMLLogger(_Logger):
             for aname, avalue in attrs.items():
                 args = (xmlquote(aname), xmlquoteattr(avalue))
                 self.write(' %s="%s"' % args)
-        self.writeln(">%s</%s>" % (xmlquote(content), xmlquote(name)))
+        self.writeln(f">{xmlquote(content)}</{xmlquote(name)}>")
diff --git a/linkcheck/plugins/anchorcheck.py b/linkcheck/plugins/anchorcheck.py
index 35248c62..e9a8a200 100644
--- a/linkcheck/plugins/anchorcheck.py
+++ b/linkcheck/plugins/anchorcheck.py
@@ -66,7 +66,7 @@ class UrlAnchorCheck:
         else:
             anchors = "-"
         args = {"name": url_data.anchor, "decoded": decoded_anchor, "anchors": anchors}
-        msg = "%s %s" % (
+        msg = "{} {}".format(
             _("Anchor `%(name)s' (decoded: `%(decoded)s') not found.") % args,
             _("Available anchors: %(anchors)s.") % args,
         )
diff --git a/linkcheck/plugins/httpheaderinfo.py b/linkcheck/plugins/httpheaderinfo.py
index 7e299d47..0c925274 100644
--- a/linkcheck/plugins/httpheaderinfo.py
+++ b/linkcheck/plugins/httpheaderinfo.py
@@ -39,7 +39,7 @@ class HttpHeaderInfo(_ConnectionPlugin):
                 headers.append(name.lower())
         if headers:
             items = [
-                "%s=%s" % (name.capitalize(), url_data.headers[name])
+                f"{name.capitalize()}={url_data.headers[name]}"
                 for name in headers
             ]
             info = "HTTP headers %s" % ", ".join(items)
diff --git a/linkcheck/strformat.py b/linkcheck/strformat.py
index f16d6e3e..0783fab7 100644
--- a/linkcheck/strformat.py
+++ b/linkcheck/strformat.py
@@ -73,10 +73,10 @@ def unquote(s, matching=False):
     return s
 
 
-_para_mac = r"(?:%(sep)s)(?:(?:%(sep)s)\s*)+" % {'sep': '\r'}
-_para_posix = r"(?:%(sep)s)(?:(?:%(sep)s)\s*)+" % {'sep': '\n'}
-_para_win = r"(?:%(sep)s)(?:(?:%(sep)s)\s*)+" % {'sep': '\r\n'}
-_para_ro = re.compile("%s|%s|%s" % (_para_mac, _para_posix, _para_win))
+_para_mac = r"(?:{sep})(?:(?:{sep})\s*)+".format(sep='\r')
+_para_posix = r"(?:{sep})(?:(?:{sep})\s*)+".format(sep='\n')
+_para_win = r"(?:{sep})(?:(?:{sep})\s*)+".format(sep='\r\n')
+_para_ro = re.compile(f"{_para_mac}|{_para_posix}|{_para_win}")
 
 
 def get_paragraphs(text):
@@ -104,7 +104,7 @@ def wrap(text, width, **kwargs):
 
 def indent(text, indent_string="  "):
     """Indent each line of text with the given indent string."""
-    return os.linesep.join("%s%s" % (indent_string, x) for x in text.splitlines())
+    return os.linesep.join(f"{indent_string}{x}" for x in text.splitlines())
 
 
 def paginate(text):
@@ -191,7 +191,7 @@ def strduration_long(duration, do_translate=True):
     time_str.reverse()
     if len(time_str) > 2:
         time_str.pop()
-    return "%s%s" % (prefix, ", ".join(time_str))
+    return "{}{}".format(prefix, ", ".join(time_str))
 
 
 def strtimezone():
diff --git a/linkcheck/url.py b/linkcheck/url.py
index e6ad1df5..ed1e52dd 100644
--- a/linkcheck/url.py
+++ b/linkcheck/url.py
@@ -61,10 +61,10 @@ _safe_path_pattern = (
     r"(%%[%(_hex_safe)s][%(_hex_full)s]))+)*/?)" % _basic
 )
 _safe_fragment_pattern = r"%s*" % _safe_char
-_safe_cgi = r"%s+(=(%s|/)+)?" % (_safe_char, _safe_char)
-_safe_query_pattern = r"(%s(&%s)*)?" % (_safe_cgi, _safe_cgi)
-_safe_param_pattern = r"(%s(;%s)*)?" % (_safe_cgi, _safe_cgi)
-safe_url_pattern = r"%s://%s%s(#%s)?" % (
+_safe_cgi = fr"{_safe_char}+(=({_safe_char}|/)+)?"
+_safe_query_pattern = fr"({_safe_cgi}(&{_safe_cgi})*)?"
+_safe_param_pattern = fr"({_safe_cgi}(;{_safe_cgi})*)?"
+safe_url_pattern = r"{}://{}{}(#{})?".format(
     _safe_scheme_pattern,
     _safe_host_pattern,
     _safe_path_pattern,
@@ -195,7 +195,7 @@ def url_fix_host(urlparts, encoding):
         if not urlparts[2] or urlparts[2] == '/':
             urlparts[2] = comps
         else:
-            urlparts[2] = "%s%s" % (
+            urlparts[2] = "{}{}".format(
                 comps,
                 urllib.parse.unquote(urlparts[2], encoding=encoding),
             )
@@ -255,12 +255,12 @@ def url_parse_query(query, encoding):
         k = urllib.parse.quote(k, safe='/-:,;')
         if v:
             v = urllib.parse.quote(v, safe='/-:,;')
-            f.append("%s=%s%s" % (k, v, sep))
+            f.append(f"{k}={v}{sep}")
         elif v is None:
-            f.append("%s%s" % (k, sep))
+            f.append(f"{k}{sep}")
         else:
             # some sites do not work when the equal sign is missing
-            f.append("%s=%s" % (k, sep))
+            f.append(f"{k}={sep}")
     return ''.join(f) + append
 
 
@@ -381,9 +381,9 @@ def url_quote(url, encoding):
         k = urllib.parse.quote(k, safe='/-:,;')
         if v:
             v = urllib.parse.quote(v, safe='/-:,;')
-            f.append("%s=%s%s" % (k, v, sep))
+            f.append(f"{k}={v}{sep}")
         else:
-            f.append("%s%s" % (k, sep))
+            f.append(f"{k}{sep}")
     urlparts[3] = ''.join(f)
     urlparts[4] = urllib.parse.quote(urlparts[4])  # anchor
     return urlunsplit(urlparts)
@@ -397,7 +397,7 @@ def document_quote(document):
         query = None
     doc = urllib.parse.quote(doc, safe='/=,')
     if query:
-        return "%s?%s" % (doc, query)
+        return f"{doc}?{query}"
     return doc
 
 
diff --git a/scripts/update_iana_uri_schemes.py b/scripts/update_iana_uri_schemes.py
index 261e5d0a..48b5cc12 100644
--- a/scripts/update_iana_uri_schemes.py
+++ b/scripts/update_iana_uri_schemes.py
@@ -87,7 +87,7 @@ def main(args):
 
 def get_regex(schemes):
     expr = [
-        "|%s # %s" % (re.escape(scheme).ljust(10), description)
+        f"|{re.escape(scheme).ljust(10)} # {description}"
         for scheme, description in sorted(schemes.items())
     ]
     return "\n".join(expr)
diff --git a/tests/checker/httpserver.py b/tests/checker/httpserver.py
index 4a28d5e4..6b58dd63 100644
--- a/tests/checker/httpserver.py
+++ b/tests/checker/httpserver.py
@@ -132,7 +132,7 @@ class NoQueryHttpRequestHandler(StoppableHttpRequestHandler):
         list = ["example1.txt", "example2.html", "example3"]
         for name in list:
             displayname = linkname = name
-            list_item = '<li><a href="%s">%s</a>\n' % (
+            list_item = '<li><a href="{}">{}</a>\n'.format(
                 urllib.parse.quote(linkname),
                 html.escape(displayname),
             )
@@ -247,7 +247,7 @@ def get_cookie(maxage=2000):
         ("Version", "1"),
         ("Foo", "Bar"),
     )
-    return "; ".join('%s="%s"' % (key, value) for key, value in data)
+    return "; ".join(f'{key}="{value}"' for key, value in data)
 
 
 class CookieRedirectHttpRequestHandler(NoQueryHttpRequestHandler):
diff --git a/tests/checker/telnetserver.py b/tests/checker/telnetserver.py
index 15f12dc1..fa23851c 100644
--- a/tests/checker/telnetserver.py
+++ b/tests/checker/telnetserver.py
@@ -40,9 +40,9 @@ class TelnetServerTest(LinkCheckTest):
     def get_url(self, user=None, password=None):
         if user is not None:
             if password is not None:
-                netloc = "%s:%s@%s" % (user, password, self.host)
+                netloc = f"{user}:{password}@{self.host}"
             else:
-                netloc = "%s@%s" % (user, self.host)
+                netloc = f"{user}@{self.host}"
         else:
             netloc = self.host
         return "telnet://%s:%d" % (netloc, self.port)
diff --git a/tests/checker/test_httpbin.py b/tests/checker/test_httpbin.py
index 7b449585..e24f4a7e 100644
--- a/tests/checker/test_httpbin.py
+++ b/tests/checker/test_httpbin.py
@@ -54,7 +54,7 @@ class TestHttpbin(LinkCheckTest):
     def test_basic_auth(self):
         user = "testuser"
         password = "testpassword"
-        url = get_httpbin_url("/basic-auth/%s/%s" % (user, password))
+        url = get_httpbin_url(f"/basic-auth/{user}/{password}")
         nurl = self.norm(url)
         entry = dict(user=user, password=password, pattern=re.compile(r".*"))
         confargs = dict(authentication=[entry])
diff --git a/tests/configuration/test_config.py b/tests/configuration/test_config.py
index 959c7e05..4a2fbf27 100644
--- a/tests/configuration/test_config.py
+++ b/tests/configuration/test_config.py
@@ -64,7 +64,7 @@ class TestConfig(TestBase):
         patterns = [x["pattern"].pattern for x in config["externlinks"]]
         for prefix in ("ignore_", "nofollow_"):
             for suffix in ("1", "2"):
-                key = "%simadoofus%s" % (prefix, suffix)
+                key = f"{prefix}imadoofus{suffix}"
                 self.assertTrue(key in patterns)
         for key in ("url-unicode-domain",):
             self.assertTrue(key in config["ignorewarnings"])
diff --git a/tests/htmllib.py b/tests/htmllib.py
index a59d03dc..16d56c0d 100644
--- a/tests/htmllib.py
+++ b/tests/htmllib.py
@@ -37,9 +37,9 @@ def pretty_print_html(fd, soup):
             if val is None:
                 fd.write(" %s" % key)
             else:
-                fd.write(' %s="%s"' % (key, quote_attrval(val)))
+                fd.write(f' {key}="{quote_attrval(val)}"')
         if element_text:
-            fd.write(">%s</%s>" % (element_text, tag))
+            fd.write(f">{element_text}</{tag}>")
         else:
             fd.write("/>")
 
diff --git a/tests/test_ftpparse.py b/tests/test_ftpparse.py
index 7a9b617f..56ed3ba9 100644
--- a/tests/test_ftpparse.py
+++ b/tests/test_ftpparse.py
@@ -125,5 +125,5 @@ class TestFtpparse(unittest.TestCase):
         for line, expected in patterns:
             res = ftpparse(line)
             self.assertEqual(
-                expected, res, "got %r\nexpected %r\n%r" % (res, expected, line)
+                expected, res, f"got {res!r}\nexpected {expected!r}\n{line!r}"
             )
diff --git a/tests/test_parser.py b/tests/test_parser.py
index 40bc922c..465656a8 100644
--- a/tests/test_parser.py
+++ b/tests/test_parser.py
@@ -165,7 +165,7 @@ class TestParser(unittest.TestCase):
         Check parse results.
         """
         res = out.getvalue()
-        msg = "Test error; in: %r, out: %r, expect: %r" % (_in, res, _out)
+        msg = f"Test error; in: {_in!r}, out: {res!r}, expect: {_out!r}"
         self.assertEqual(res, _out, msg=msg)
 
     def test_encoding_detection_utf_content(self):
diff --git a/tests/test_po.py b/tests/test_po.py
index 30d5f459..e5b49103 100644
--- a/tests/test_po.py
+++ b/tests/test_po.py
@@ -70,5 +70,5 @@ class TestGTranslator(unittest.TestCase):
                 continue
             self.assertFalse(
                 "·" in line,
-                "Broken GTranslator copy/paste in %r:\n%s" % (f, line),
+                f"Broken GTranslator copy/paste in {f!r}:\n{line}",
             )
diff --git a/tests/test_robotparser.py b/tests/test_robotparser.py
index bebf3afd..c6b452ea 100644
--- a/tests/test_robotparser.py
+++ b/tests/test_robotparser.py
@@ -40,7 +40,7 @@ class TestRobotParser(unittest.TestCase):
         else:
             ac = "access allowed"
         if a != b:
-            self.fail("%s != %s (%s)" % (a, b, ac))
+            self.fail(f"{a} != {b} ({ac})")
 
     @need_network
     def test_nonexisting_robots(self):