diff --git a/aerich/__init__.py b/aerich/__init__.py
index f3e045c..c6943c4 100644
--- a/aerich/__init__.py
+++ b/aerich/__init__.py
@@ -1,6 +1,6 @@
 import os
 from pathlib import Path
-from typing import List
+from typing import TYPE_CHECKING, List, Optional, Type
 
 from tortoise import Tortoise, generate_schema_for_client
 from tortoise.exceptions import OperationalError
@@ -20,6 +20,9 @@ from aerich.utils import (
     import_py_file,
 )
 
+if TYPE_CHECKING:
+    from aerich.inspectdb import Inspect  # noqa:F401
+
 
 class Command:
     def __init__(
@@ -27,16 +30,16 @@ class Command:
         tortoise_config: dict,
         app: str = "models",
         location: str = "./migrations",
-    ):
+    ) -> None:
         self.tortoise_config = tortoise_config
         self.app = app
         self.location = location
         Migrate.app = app
 
-    async def init(self):
+    async def init(self) -> None:
         await Migrate.init(self.tortoise_config, self.app, self.location)
 
-    async def _upgrade(self, conn, version_file):
+    async def _upgrade(self, conn, version_file) -> None:
         file_path = Path(Migrate.migrate_location, version_file)
         m = import_py_file(file_path)
         upgrade = getattr(m, "upgrade")
@@ -47,7 +50,7 @@ class Command:
             content=get_models_describe(self.app),
         )
 
-    async def upgrade(self, run_in_transaction: bool = True):
+    async def upgrade(self, run_in_transaction: bool = True) -> List[str]:
         migrated = []
         for version_file in Migrate.get_all_version_files():
             try:
@@ -65,8 +68,8 @@ class Command:
                 migrated.append(version_file)
         return migrated
 
-    async def downgrade(self, version: int, delete: bool):
-        ret = []
+    async def downgrade(self, version: int, delete: bool) -> List[str]:
+        ret: List[str] = []
         if version == -1:
             specified_version = await Migrate.get_last_version()
         else:
@@ -79,8 +82,8 @@ class Command:
             versions = [specified_version]
         else:
             versions = await Aerich.filter(app=self.app, pk__gte=specified_version.pk)
-        for version in versions:
-            file = version.version
+        for version_obj in versions:
+            file = version_obj.version
             async with in_transaction(
                 get_app_connection_name(self.tortoise_config, self.app)
             ) as conn:
@@ -91,13 +94,13 @@ class Command:
                 if not downgrade_sql.strip():
                     raise DowngradeError("No downgrade items found")
                 await conn.execute_script(downgrade_sql)
-                await version.delete()
+                await version_obj.delete()
                 if delete:
                     os.unlink(file_path)
                 ret.append(file)
         return ret
 
-    async def heads(self):
+    async def heads(self) -> List[str]:
         ret = []
         versions = Migrate.get_all_version_files()
         for version in versions:
@@ -105,15 +108,15 @@ class Command:
                 ret.append(version)
         return ret
 
-    async def history(self):
+    async def history(self) -> List[str]:
         versions = Migrate.get_all_version_files()
         return [version for version in versions]
 
-    async def inspectdb(self, tables: List[str] = None) -> str:
+    async def inspectdb(self, tables: Optional[List[str]] = None) -> str:
         connection = get_app_connection(self.tortoise_config, self.app)
         dialect = connection.schema_generator.DIALECT
         if dialect == "mysql":
-            cls = InspectMySQL
+            cls: Type["Inspect"] = InspectMySQL
         elif dialect == "postgres":
             cls = InspectPostgres
         elif dialect == "sqlite":
@@ -126,7 +129,7 @@ class Command:
     async def migrate(self, name: str = "update", empty: bool = False) -> str:
         return await Migrate.migrate(name, empty)
 
-    async def init_db(self, safe: bool):
+    async def init_db(self, safe: bool) -> None:
         location = self.location
         app = self.app
         dirname = Path(location, app)
diff --git a/aerich/cli.py b/aerich/cli.py
index 924f044..c40ce8e 100644
--- a/aerich/cli.py
+++ b/aerich/cli.py
@@ -2,7 +2,7 @@ import asyncio
 import os
 from functools import wraps
 from pathlib import Path
-from typing import List
+from typing import Dict, List, cast
 
 import click
 import tomlkit
@@ -23,7 +23,7 @@ CONFIG_DEFAULT_VALUES = {
 
 def coro(f):
     @wraps(f)
-    def wrapper(*args, **kwargs):
+    def wrapper(*args, **kwargs) -> None:
         loop = asyncio.get_event_loop()
 
         # Close db connections at the end of all but the cli group function
@@ -48,7 +48,7 @@ def coro(f):
 @click.option("--app", required=False, help="Tortoise-ORM app name.")
 @click.pass_context
 @coro
-async def cli(ctx: Context, config, app):
+async def cli(ctx: Context, config, app) -> None:
     ctx.ensure_object(dict)
     ctx.obj["config_file"] = config
 
@@ -58,9 +58,9 @@ async def cli(ctx: Context, config, app):
         if not config_path.exists():
             raise UsageError("You must exec init first", ctx=ctx)
         content = config_path.read_text()
-        doc = tomlkit.parse(content)
+        doc: dict = tomlkit.parse(content)
         try:
-            tool = doc["tool"]["aerich"]
+            tool = cast(Dict[str, str], doc["tool"]["aerich"])
             location = tool["location"]
             tortoise_orm = tool["tortoise_orm"]
             src_folder = tool.get("src_folder", CONFIG_DEFAULT_VALUES["src_folder"])
@@ -68,7 +68,9 @@ async def cli(ctx: Context, config, app):
             raise UsageError("You need run aerich init again when upgrade to 0.6.0+")
         add_src_path(src_folder)
         tortoise_config = get_tortoise_config(ctx, tortoise_orm)
-        app = app or list(tortoise_config.get("apps").keys())[0]
+        if not app:
+            apps_config = cast(dict, tortoise_config.get("apps"))
+            app = list(apps_config.keys())[0]
         command = Command(tortoise_config=tortoise_config, app=app, location=location)
         ctx.obj["command"] = command
         if invoked_subcommand != "init-db":
@@ -82,7 +84,7 @@ async def cli(ctx: Context, config, app):
 @click.option("--empty", default=False, is_flag=True, help="Generate empty migration file.")
 @click.pass_context
 @coro
-async def migrate(ctx: Context, name):
+async def migrate(ctx: Context, name) -> None:
     command = ctx.obj["command"]
     ret = await command.migrate(name)
     if not ret:
@@ -100,7 +102,7 @@ async def migrate(ctx: Context, name):
 )
 @click.pass_context
 @coro
-async def upgrade(ctx: Context, in_transaction: bool):
+async def upgrade(ctx: Context, in_transaction: bool) -> None:
     command = ctx.obj["command"]
     migrated = await command.upgrade(run_in_transaction=in_transaction)
     if not migrated:
@@ -132,7 +134,7 @@ async def upgrade(ctx: Context, in_transaction: bool):
     prompt="Downgrade is dangerous, which maybe lose your data, are you sure?",
 )
 @coro
-async def downgrade(ctx: Context, version: int, delete: bool):
+async def downgrade(ctx: Context, version: int, delete: bool) -> None:
     command = ctx.obj["command"]
     try:
         files = await command.downgrade(version, delete)
@@ -145,7 +147,7 @@ async def downgrade(ctx: Context, version: int, delete: bool):
 @cli.command(help="Show current available heads in migrate location.")
 @click.pass_context
 @coro
-async def heads(ctx: Context):
+async def heads(ctx: Context) -> None:
     command = ctx.obj["command"]
     head_list = await command.heads()
     if not head_list:
@@ -157,7 +159,7 @@ async def heads(ctx: Context):
 @cli.command(help="List all migrate items.")
 @click.pass_context
 @coro
-async def history(ctx: Context):
+async def history(ctx: Context) -> None:
     command = ctx.obj["command"]
     versions = await command.history()
     if not versions:
@@ -188,7 +190,7 @@ async def history(ctx: Context):
 )
 @click.pass_context
 @coro
-async def init(ctx: Context, tortoise_orm, location, src_folder):
+async def init(ctx: Context, tortoise_orm, location, src_folder) -> None:
     config_file = ctx.obj["config_file"]
 
     if os.path.isabs(src_folder):
@@ -203,9 +205,9 @@ async def init(ctx: Context, tortoise_orm, location, src_folder):
     config_path = Path(config_file)
     if config_path.exists():
         content = config_path.read_text()
-        doc = tomlkit.parse(content)
     else:
-        doc = tomlkit.parse("[tool.aerich]")
+        content = "[tool.aerich]"
+    doc: dict = tomlkit.parse(content)
     table = tomlkit.table()
     table["tortoise_orm"] = tortoise_orm
     table["location"] = location
@@ -232,7 +234,7 @@ async def init(ctx: Context, tortoise_orm, location, src_folder):
 )
 @click.pass_context
 @coro
-async def init_db(ctx: Context, safe: bool):
+async def init_db(ctx: Context, safe: bool) -> None:
     command = ctx.obj["command"]
     app = command.app
     dirname = Path(command.location, app)
@@ -256,13 +258,13 @@ async def init_db(ctx: Context, safe: bool):
 )
 @click.pass_context
 @coro
-async def inspectdb(ctx: Context, table: List[str]):
+async def inspectdb(ctx: Context, table: List[str]) -> None:
     command = ctx.obj["command"]
     ret = await command.inspectdb(table)
     click.secho(ret)
 
 
-def main():
+def main() -> None:
     cli()
 
 
diff --git a/aerich/coder.py b/aerich/coder.py
index 3501c24..870ee7a 100644
--- a/aerich/coder.py
+++ b/aerich/coder.py
@@ -1,12 +1,13 @@
 import base64
 import json
 import pickle  # nosec: B301,B403
+from typing import Any, Union
 
 from tortoise.indexes import Index
 
 
 class JsonEncoder(json.JSONEncoder):
-    def default(self, obj):
+    def default(self, obj) -> Any:
         if isinstance(obj, Index):
             return {
                 "type": "index",
@@ -16,16 +17,16 @@ class JsonEncoder(json.JSONEncoder):
             return super().default(obj)
 
 
-def object_hook(obj):
+def object_hook(obj) -> Any:
     _type = obj.get("type")
     if not _type:
         return obj
     return pickle.loads(base64.b64decode(obj["val"]))  # nosec: B301
 
 
-def encoder(obj: dict):
+def encoder(obj: dict) -> str:
     return json.dumps(obj, cls=JsonEncoder)
 
 
-def decoder(obj: str):
+def decoder(obj: Union[str, bytes]) -> Any:
     return json.loads(obj, object_hook=object_hook)
diff --git a/aerich/utils.py b/aerich/utils.py
index ac5fb87..14664a0 100644
--- a/aerich/utils.py
+++ b/aerich/utils.py
@@ -3,7 +3,8 @@ import os
 import re
 import sys
 from pathlib import Path
-from typing import Dict
+from types import ModuleType
+from typing import Dict, Optional
 
 from click import BadOptionUsage, ClickException, Context
 from tortoise import BaseDBAsyncClient, Tortoise
@@ -84,19 +85,19 @@ def get_models_describe(app: str) -> Dict:
     :return:
     """
     ret = {}
-    for model in Tortoise.apps.get(app).values():
+    for model in Tortoise.apps[app].values():
         describe = model.describe()
         ret[describe.get("name")] = describe
     return ret
 
 
-def is_default_function(string: str):
+def is_default_function(string: str) -> Optional[re.Match]:
     return re.match(r"^<function.+>$", str(string or ""))
 
 
-def import_py_file(file: Path):
+def import_py_file(file: Path) -> ModuleType:
     module_name, file_ext = os.path.splitext(os.path.split(file)[-1])
     spec = importlib.util.spec_from_file_location(module_name, file)
-    module = importlib.util.module_from_spec(spec)
-    spec.loader.exec_module(module)
+    module = importlib.util.module_from_spec(spec)  # type:ignore[arg-type]
+    spec.loader.exec_module(module)  # type:ignore[union-attr]
     return module