diff --git a/requirements.txt b/requirements.txt
index 32c4523a9..12b1f7302 100644
--- a/requirements.txt
+++ b/requirements.txt
@@ -9,8 +9,8 @@ pytest-cov
 -e ./zulip
 -e ./zulip_bots
 -e ./zulip_botserver
--e git+https://github.com/zulip/zulint@14e3974001bf8442a6a3486125865660f1f2eb68#egg=zulint==1.0.0
-mypy==0.910
+-e git+https://github.com/zulip/zulint@85de0cbadbba3f498deba32f861bb9a478faa3b4#egg=zulint==1.0.0
+mypy==1.6.1
 types-python-dateutil
 types-pytz
 types-requests
diff --git a/tools/custom_check.py b/tools/custom_check.py
index f53bbc7ee..2e8efd169 100644
--- a/tools/custom_check.py
+++ b/tools/custom_check.py
@@ -4,24 +4,22 @@
 
 whitespace_rules: List[Rule] = [
     # This linter should be first since bash_rules depends on it.
-    {"pattern": r"\s+$", "strip": "\n", "description": "Fix trailing whitespace"},
-    {"pattern": "\t", "strip": "\n", "description": "Fix tab-based whitespace"},
+    {"pattern": r"[\t ]+$", "description": "Fix trailing whitespace"},
+    {"pattern": r"\t", "description": "Fix tab-based whitespace"},
 ]
 
 markdown_whitespace_rules = list(
-    rule for rule in whitespace_rules if rule["pattern"] != r"\s+$"
+    rule for rule in whitespace_rules if rule["pattern"] != r"[\t ]+$"
 ) + [
     # Two spaces trailing a line with other content is okay--it's a markdown line break.
     # This rule finds one space trailing a non-space, three or more trailing spaces, and
     # spaces on an empty line.
     {
-        "pattern": r"((?<!\s)\s$)|(\s\s\s+$)|(^\s+$)",
-        "strip": "\n",
+        "pattern": r"((?<![\t ])[\t ]$)|([\t ][\t ][\t ]+$)|(^[\t ]+$)",
         "description": "Fix trailing whitespace",
     },
     {
         "pattern": r"^#+[A-Za-z0-9]",
-        "strip": "\n",
         "description": "Missing space after # in heading",
     },
 ]
@@ -29,13 +27,6 @@
 python_rules = RuleList(
     langs=["py"],
     rules=[
-        {"pattern": r'".*"%\([a-z_].*\)?$', "description": 'Missing space around "%"'},
-        {"pattern": r"'.*'%\([a-z_].*\)?$", "description": 'Missing space around "%"'},
-        # This rule is constructed with + to avoid triggering on itself
-        {"pattern": r" =" + r'[^ =>~"]', "description": 'Missing whitespace after "="'},
-        {"pattern": r'":\w[^"]*$', "description": 'Missing whitespace after ":"'},
-        {"pattern": r"':\w[^']*$", "description": 'Missing whitespace after ":"'},
-        {"pattern": r"^\s+[#]\w", "strip": "\n", "description": 'Missing whitespace after "#"'},
         {
             "pattern": r"assertEquals[(]",
             "description": "Use assertEqual, not assertEquals (which is deprecated).",
@@ -46,13 +37,6 @@
             "good_lines": ["def foo (self):"],
             "bad_lines": ["def foo(self: Any):"],
         },
-        {"pattern": r"== None", "description": "Use `is None` to check whether something is None"},
-        {"pattern": r"type:[(]", "description": 'Missing whitespace after ":" in type annotation'},
-        {"pattern": r"# type [(]", "description": "Missing : after type in type annotation"},
-        {"pattern": r"#type", "description": 'Missing whitespace after "#" in type annotation'},
-        {"pattern": r"if[(]", "description": "Missing space between if and ("},
-        {"pattern": r", [)]", "description": 'Unnecessary whitespace between "," and ")"'},
-        {"pattern": r"%  [(]", "description": 'Unnecessary whitespace between "%" and "("'},
         # This next check could have false positives, but it seems pretty
         # rare; if we find any, they can be added to the exclude list for
         # this rule.
@@ -97,7 +81,6 @@
         },
         *whitespace_rules,
     ],
-    max_length=140,
 )
 
 bash_rules = RuleList(
@@ -145,10 +128,6 @@
     },
 ]
 
-markdown_docs_length_exclude = {
-    "zulip_bots/zulip_bots/bots/converter/doc.md",
-}
-
 markdown_rules = RuleList(
     langs=["md"],
     rules=[
@@ -159,8 +138,6 @@
             "description": "Linkified markdown URLs should use cleaner <http://example.com> syntax.",
         },
     ],
-    max_length=120,
-    length_exclude=markdown_docs_length_exclude,
 )
 
 txt_rules = RuleList(
diff --git a/zulip/tests/__init__.py b/zulip/tests/__init__.py
index 832c764d2..f77af49c2 100644
--- a/zulip/tests/__init__.py
+++ b/zulip/tests/__init__.py
@@ -1,4 +1,3 @@
 import pkgutil
-from typing import List
 
-__path__: List[str] = pkgutil.extend_path(__path__, __name__)
+__path__ = pkgutil.extend_path(__path__, __name__)
diff --git a/zulip_botserver/tests/__init__.py b/zulip_botserver/tests/__init__.py
index 832c764d2..f77af49c2 100644
--- a/zulip_botserver/tests/__init__.py
+++ b/zulip_botserver/tests/__init__.py
@@ -1,4 +1,3 @@
 import pkgutil
-from typing import List
 
-__path__: List[str] = pkgutil.extend_path(__path__, __name__)
+__path__ = pkgutil.extend_path(__path__, __name__)
diff --git a/zulip_botserver/zulip_botserver/server.py b/zulip_botserver/zulip_botserver/server.py
index 85f49d0b6..08f1d233d 100644
--- a/zulip_botserver/zulip_botserver/server.py
+++ b/zulip_botserver/zulip_botserver/server.py
@@ -149,7 +149,9 @@ def load_bot_handlers(
             api_key=bots_config[bot]["key"],
             site=bots_config[bot]["site"],
         )
-        bot_dir = os.path.join(os.path.dirname(os.path.abspath(bot_lib_modules[bot].__file__)))
+        bot_file = bot_lib_modules[bot].__file__
+        assert bot_file is not None
+        bot_dir = os.path.dirname(os.path.abspath(bot_file))
         bot_handler = lib.ExternalBotHandler(
             client, bot_dir, bot_details={}, bot_config_parser=third_party_bot_conf
         )