diff --git a/pyproject.toml b/pyproject.toml
new file mode 100644
index 0000000..7c955ab
--- /dev/null
+++ b/pyproject.toml
@@ -0,0 +1,18 @@
+[tool.mypy]
+check_untyped_defs = true
+disallow_any_generics = true
+disallow_untyped_calls = true
+disallow_untyped_defs = true
+ignore_missing_imports = true
+no_implicit_optional = true
+no_implicit_reexport = true
+show_column_numbers = true
+show_error_codes = true
+show_traceback = true
+strict = true
+strict_equality = true
+warn_redundant_casts = true
+warn_return_any = true
+warn_unreachable = true
+warn_unused_configs = true
+warn_unused_ignores = true
diff --git a/rere.py b/rere.py
index 4df44ae..698f014 100755
--- a/rere.py
+++ b/rere.py
@@ -23,7 +23,7 @@
 import sys
 import subprocess
 from difflib import unified_diff
-from typing import List, BinaryIO, Tuple, Optional
+from typing import BinaryIO, TypedDict
 
 def read_blob_field(f: BinaryIO, name: bytes) -> bytes:
     line = f.readline()
@@ -42,15 +42,21 @@ def read_int_field(f: BinaryIO, name: bytes) -> int:
     assert line.endswith(b'\n')
     return int(line[len(field):-1])
 
-def write_int_field(f: BinaryIO, name: bytes, value: int):
+def write_int_field(f: BinaryIO, name: bytes, value: int) -> None:
     f.write(b':i %s %d\n' % (name, value))
 
-def write_blob_field(f: BinaryIO, name: bytes, blob: bytes):
+def write_blob_field(f: BinaryIO, name: bytes, blob: bytes) -> None:
     f.write(b':b %s %d\n' % (name, len(blob)))
     f.write(blob)
     f.write(b'\n')
 
-def capture(shell: str) -> dict:
+class Snapshot(TypedDict):
+    shell: str
+    returncode: int
+    stdout: bytes
+    stderr: bytes
+
+def capture(shell: str) -> Snapshot:
     print(f"CAPTURING: {shell}")
     process = subprocess.run(['sh', '-c', shell], capture_output = True)
     return {
@@ -64,7 +70,7 @@ def load_list(file_path: str) -> list[str]:
     with open(file_path) as f:
         return [line.strip() for line in f]
 
-def dump_snapshots(file_path: str, snapshots: list[dict]):
+def dump_snapshots(file_path: str, snapshots: list[Snapshot]) -> None:
     with open(file_path, "wb") as f:
         write_int_field(f, b"count", len(snapshots))
         for snapshot in snapshots:
@@ -73,21 +79,21 @@ def dump_snapshots(file_path: str, snapshots: list[dict]):
             write_blob_field(f, b"stdout", snapshot['stdout'])
             write_blob_field(f, b"stderr", snapshot['stderr'])
 
-def load_snapshots(file_path: str) -> list[dict]:
+def load_snapshots(file_path: str) -> list[Snapshot]:
     snapshots = []
     with open(file_path, "rb") as f:
         count = read_int_field(f, b"count")
         for _ in range(count):
-            shell = read_blob_field(f, b"shell")
+            shell: bytes = read_blob_field(f, b"shell")
             returncode = read_int_field(f, b"returncode")
             stdout = read_blob_field(f, b"stdout")
             stderr = read_blob_field(f, b"stderr")
-            snapshot = {
-                "shell": shell,
+            snapshot = Snapshot({
+                "shell": shell.decode("utf-8"),
                 "returncode": returncode,
                 "stdout": stdout,
                 "stderr": stderr,
-            }
+            })
             snapshots.append(snapshot)
     return snapshots
 
@@ -128,7 +134,7 @@ def load_snapshots(file_path: str) -> list[dict]:
 
         for (shell, snapshot) in zip(shells, snapshots):
             print(f"REPLAYING: {shell}")
-            snapshot_shell = snapshot['shell'].decode('utf-8')
+            snapshot_shell = snapshot['shell']
             if shell != snapshot_shell:
                 print(f"UNEXPECTED: shell command")
                 print(f"    EXPECTED: {snapshot_shell}")