diff --git a/src/runboat/api.py b/src/runboat/api.py
index 15dd2ac..7bced44 100644
--- a/src/runboat/api.py
+++ b/src/runboat/api.py
@@ -118,10 +118,10 @@ async def trigger_pull(org: str, repo: str, pr: int):
 
 
 def _build_by_name(name: str) -> models.Build:
-    try:
-        return controller.db.get(name)
-    except KeyError:
+    build = controller.db.get(name)
+    if build is None:
         raise HTTPException(status.HTTP_404_NOT_FOUND)
+    return build
 
 
 @router.get("/builds/{name}", response_model=Build)
diff --git a/src/runboat/controller.py b/src/runboat/controller.py
index 23284cb..426b932 100644
--- a/src/runboat/controller.py
+++ b/src/runboat/controller.py
@@ -27,17 +27,17 @@ class Controller:
     _tasks: list[asyncio.Task]
     _wakeup_event: asyncio.Event
 
-    def __init__(self):
+    def __init__(self) -> None:
         self._tasks = []
         self._wakeup_event = asyncio.Event()
         self.reset()
 
-    def reset(self):
+    def reset(self) -> None:
         self.db = BuildsDb()
 
     @property
     def running(self) -> int:
-        return self.db.count_by_statuses([BuildStatus.started, BuildStatus.starting])
+        return self.db.count_by_statuses((BuildStatus.started, BuildStatus.starting))
 
     @property
     def max_running(self) -> int:
@@ -45,7 +45,7 @@ class Controller:
 
     @property
     def starting(self) -> int:
-        return self.db.count_by_statuses([BuildStatus.starting])
+        return self.db.count_by_statuses((BuildStatus.starting,))
 
     @property
     def max_starting(self) -> int:
@@ -131,7 +131,7 @@ class Controller:
                 if len(to_undeploy) < can_undeploy:
                     break  # back to sleep
 
-    async def start(self):
+    async def start(self) -> None:
         _logger.info("Starting controller tasks.")
 
         async def walking_dead(func):
@@ -148,7 +148,7 @@ class Controller:
         for f in (self.watcher, self.starter, self.stopper, self.undeployer):
             self._tasks.append(asyncio.create_task(walking_dead(f)))
 
-    async def stop(self):
+    async def stop(self) -> None:
         _logger.info("Stopping controller tasks.")
         for task in self._tasks:
             task.cancel()
diff --git a/src/runboat/db.py b/src/runboat/db.py
index 40301ee..a0a568e 100644
--- a/src/runboat/db.py
+++ b/src/runboat/db.py
@@ -16,7 +16,7 @@ class BuildsDb:
 
     _con: sqlite3.Connection
 
-    def __init__(self):
+    def __init__(self) -> None:
         self.reset()
 
     @classmethod
@@ -88,7 +88,7 @@ class BuildsDb:
                 ),
             )
 
-    def count_by_statuses(self, statuses: tuple[BuildStatus]) -> int:
+    def count_by_statuses(self, statuses: tuple[BuildStatus, ...]) -> int:
         q = ",".join(["?"] * len(statuses))
         return self._con.execute(
             f"SELECT COUNT(name) FROM builds WHERE status IN ({q})", statuses
@@ -123,7 +123,7 @@ class BuildsDb:
 
     def branches_and_pulls(self, repo: str) -> list[BranchOrPull]:
         res = []
-        branch_or_pull: BranchOrPull = None
+        branch_or_pull: BranchOrPull | None = None
         for row in self._con.execute(
             "SELECT * FROM builds WHERE repo=?"
             "ORDER BY target_branch, pr, created DESC",
diff --git a/src/runboat/k8s.py b/src/runboat/k8s.py
index 0202f41..7bf6f62 100644
--- a/src/runboat/k8s.py
+++ b/src/runboat/k8s.py
@@ -5,7 +5,7 @@ import tempfile
 from contextlib import contextmanager
 from importlib import resources
 from pathlib import Path
-from typing import Any, AsyncGenerator, ContextManager, Dict, List, Optional, Tuple
+from typing import Any, AsyncGenerator, Dict, Generator, List, Optional, Tuple
 
 from jinja2 import Template
 from kubernetes_asyncio import client, config, watch
@@ -95,7 +95,7 @@ def make_deployment_vars(
 
 
 @contextmanager
-def _render_kubefiles(deployment_vars: DeploymentVars) -> ContextManager[Path]:
+def _render_kubefiles(deployment_vars: DeploymentVars) -> Generator[Path, None, None]:
     with resources.path(
         __package__, "kubefiles"
     ) as kubefiles_path, tempfile.TemporaryDirectory() as tmp_dir:
@@ -111,9 +111,9 @@ def _render_kubefiles(deployment_vars: DeploymentVars) -> ContextManager[Path]:
 
 async def _kubectl(args: List[str]) -> None:
     proc = await asyncio.create_subprocess_exec("kubectl", *args)
-    await proc.wait()
-    if proc.returncode != 0:
-        raise subprocess.CalledProcessError(proc.returncode, ["kubectl"] + args)
+    return_code = await proc.wait()
+    if return_code != 0:
+        raise subprocess.CalledProcessError(return_code, ["kubectl"] + args)
 
 
 async def deploy(deployment_vars: DeploymentVars) -> None:
diff --git a/src/runboat/utils.py b/src/runboat/utils.py
index e10f070..d2b7366 100644
--- a/src/runboat/utils.py
+++ b/src/runboat/utils.py
@@ -1,5 +1,5 @@
 import re
 
 
-def slugify(s: str) -> str:
+def slugify(s: str | int) -> str:
     return re.sub(r"[^a-z0-9]", "-", str(s).lower())
diff --git a/src/runboat/webhooks.py b/src/runboat/webhooks.py
index 984bed0..885df06 100644
--- a/src/runboat/webhooks.py
+++ b/src/runboat/webhooks.py
@@ -2,7 +2,7 @@ import logging
 
 from fastapi import APIRouter, BackgroundTasks, Header, Request
 
-from . import controller
+from . import models
 from .settings import settings
 
 _logger = logging.getLogger(__name__)
@@ -15,7 +15,7 @@ async def receive_payload(
     background_tasks: BackgroundTasks,
     request: Request,
     x_github_event: str = Header(...),
-):
+) -> None:
     # TODO check x-hub-signature
     payload = await request.json()
     repo = payload["repository"]["full_name"]
@@ -29,7 +29,7 @@ async def receive_payload(
     if x_github_event == "pull_request":
         if action in ("opened", "synchronize"):
             background_tasks.add_task(
-                controller.Build.deploy,
+                models.Build.deploy,
                 repo=repo,
                 target_branch=payload["pull_request"]["base"]["ref"],
                 pr=payload["pull_request"]["number"],
@@ -37,7 +37,7 @@ async def receive_payload(
             )
     elif x_github_event == "push":
         background_tasks.add_task(
-            controller.Build.deploy,
+            models.Build.deploy,
             repo=repo,
             target_branch=payload["ref"].split("/")[-1],
             pr=None,