diff --git a/python/ruff-ecosystem/ruff_ecosystem/check.py b/python/ruff-ecosystem/ruff_ecosystem/check.py
index 2e996ff006..fe5ea0c246 100644
--- a/python/ruff-ecosystem/ruff_ecosystem/check.py
+++ b/python/ruff-ecosystem/ruff_ecosystem/check.py
@@ -63,7 +63,7 @@ def markdown_check_result(result: Result) -> str:
         project_rule_changes[project] = changes = RuleChanges.from_diff(diff)
         all_rule_changes.update(changes)
 
-    lines = []
+    lines: list[str] = []
     total_removed = all_rule_changes.total_removed_violations()
     total_added = all_rule_changes.total_added_violations()
     total_added_fixes = all_rule_changes.total_added_fixes()
diff --git a/python/ruff-ecosystem/ruff_ecosystem/format.py b/python/ruff-ecosystem/ruff_ecosystem/format.py
index f639150a86..2a15e62920 100644
--- a/python/ruff-ecosystem/ruff_ecosystem/format.py
+++ b/python/ruff-ecosystem/ruff_ecosystem/format.py
@@ -25,11 +25,11 @@ def markdown_format_result(result: Result) -> str:
     """
     Render a `ruff format` ecosystem check result as markdown.
     """
-    lines = []
+    lines: list[str] = []
     total_lines_removed = total_lines_added = 0
     total_files_modified = 0
     error_count = len(result.errored)
-    patch_sets = []
+    patch_sets: list[PatchSet] = []
 
     for project, comparison in result.completed:
         total_lines_added += comparison.diff.lines_added
@@ -97,7 +97,7 @@ def format_patchset(patch_set: PatchSet, repo: ClonedRepository) -> str:
     """
     Convert a patchset to markdown, adding permalinks to the start of each hunk.
     """
-    lines = []
+    lines: list[str] = []
     for file_patch in patch_set:
         for hunk in file_patch:
             # Note:  When used for `format` checks, the line number is not exact because
diff --git a/python/ruff-ecosystem/ruff_ecosystem/main.py b/python/ruff-ecosystem/ruff_ecosystem/main.py
index e7f50093b9..ca0e3037c7 100644
--- a/python/ruff-ecosystem/ruff_ecosystem/main.py
+++ b/python/ruff-ecosystem/ruff_ecosystem/main.py
@@ -53,7 +53,7 @@ async def main(
         async with semaphore:
             return await coroutine
 
-    comparisons: list[Exception | Comparison] = await asyncio.gather(
+    comparisons: list[BaseException | Comparison] = await asyncio.gather(
         *[
             limited_parallelism(
                 clone_and_compare(
@@ -72,9 +72,10 @@ async def main(
     comparisons_by_target = dict(zip(targets, comparisons, strict=True))
 
     # Split comparisons into errored / completed
-    errored, completed = [], []
+    errored: list[tuple[Project, BaseException]] = []
+    completed: list[tuple[Project, Comparison]] = []
     for target, comparison in comparisons_by_target.items():
-        if isinstance(comparison, Exception):
+        if isinstance(comparison, BaseException):
             errored.append((target, comparison))
         else:
             completed.append((target, comparison))
@@ -138,7 +139,7 @@ async def clone_and_compare(
 
 
 class JSONEncoder(json.JSONEncoder):
-    def default(self, o):
+    def default(self, o: object):
         if isinstance(o, Serializable):
             return o.jsonable()
         if dataclasses.is_dataclass(o):
diff --git a/python/ruff-ecosystem/ruff_ecosystem/markdown.py b/python/ruff-ecosystem/ruff_ecosystem/markdown.py
index e6f6060695..0af3b20367 100644
--- a/python/ruff-ecosystem/ruff_ecosystem/markdown.py
+++ b/python/ruff-ecosystem/ruff_ecosystem/markdown.py
@@ -3,11 +3,11 @@ from __future__ import annotations
 from typing import TYPE_CHECKING
 
 if TYPE_CHECKING:
-    from ruff_ecosystem.projects import Project
+    from ruff_ecosystem.projects import CommandOptions, Project
 
 
 def markdown_project_section(
-    title: str, content: str | list[str], options: object, project: Project
+    title: str, content: str | list[str], options: CommandOptions, project: Project
 ) -> list[str]:
     return markdown_details(
         summary=f'<a href="{project.repo.url}">{project.repo.fullname}</a> ({title})',
@@ -28,8 +28,10 @@ def markdown_plus_minus(added: int, removed: int) -> str:
     return f"+{added} -{removed}"
 
 
-def markdown_details(summary: str, content: str | list[str], preface: str):
-    lines = []
+def markdown_details(
+    summary: str, content: str | list[str], preface: str | None
+) -> list[str]:
+    lines: list[str] = []
     lines.append(f"<details><summary>{summary}</summary>")
     if preface:
         lines.append("<p>")
diff --git a/python/ruff-ecosystem/ruff_ecosystem/projects.py b/python/ruff-ecosystem/ruff_ecosystem/projects.py
index d4fb64e804..fa5f8224a8 100644
--- a/python/ruff-ecosystem/ruff_ecosystem/projects.py
+++ b/python/ruff-ecosystem/ruff_ecosystem/projects.py
@@ -104,7 +104,7 @@ class FormatOptions(CommandOptions):
         return args
 
     def to_black_args(self) -> list[str]:
-        args = []
+        args: list[str] = []
         if self.exclude:
             args.extend(["--exclude", self.exclude])
         if self.preview:
diff --git a/python/ruff-ecosystem/ruff_ecosystem/types.py b/python/ruff-ecosystem/ruff_ecosystem/types.py
index 41a9b02aab..687ab31ce8 100644
--- a/python/ruff-ecosystem/ruff_ecosystem/types.py
+++ b/python/ruff-ecosystem/ruff_ecosystem/types.py
@@ -75,7 +75,7 @@ class Result(Serializable):
     The result of an ecosystem check for a collection of projects.
     """
 
-    errored: list[tuple[Project, Exception]]
+    errored: list[tuple[Project, BaseException]]
     completed: list[tuple[Project, Comparison]]