diff --git a/babi/list_spy.py b/babi/list_spy.py
new file mode 100644
index 0000000..aaf4215
--- /dev/null
+++ b/babi/list_spy.py
@@ -0,0 +1,81 @@
+import functools
+from typing import Callable
+from typing import Iterator
+from typing import List
+from typing import TYPE_CHECKING
+
+if TYPE_CHECKING:
+    from typing import Protocol  # python3.8+
+else:
+    Protocol = object
+
+
+class MutableSequenceNoSlice(Protocol):
+    def __len__(self) -> int: ...
+    def __getitem__(self, idx: int) -> str: ...
+    def __setitem__(self, idx: int, val: str) -> None: ...
+    def __delitem__(self, idx: int) -> None: ...
+    def insert(self, idx: int, val: str) -> None: ...
+
+    def __iter__(self) -> Iterator[str]:
+        for i in range(len(self)):
+            yield self[i]
+
+    def append(self, val: str) -> None:
+        self.insert(len(self), val)
+
+    def pop(self, idx: int = -1) -> str:
+        victim = self[idx]
+        del self[idx]
+        return victim
+
+
+def _del(lst: MutableSequenceNoSlice, *, idx: int) -> None:
+    del lst[idx]
+
+
+def _set(lst: MutableSequenceNoSlice, *, idx: int, val: str) -> None:
+    lst[idx] = val
+
+
+def _ins(lst: MutableSequenceNoSlice, *, idx: int, val: str) -> None:
+    lst.insert(idx, val)
+
+
+class ListSpy(MutableSequenceNoSlice):
+    def __init__(self, lst: MutableSequenceNoSlice) -> None:
+        self._lst = lst
+        self._undo: List[Callable[[MutableSequenceNoSlice], None]] = []
+
+    def __repr__(self) -> str:
+        return f'{type(self).__name__}({self._lst})'
+
+    def __len__(self) -> int:
+        return len(self._lst)
+
+    def __getitem__(self, idx: int) -> str:
+        return self._lst[idx]
+
+    def __setitem__(self, idx: int, val: str) -> None:
+        self._undo.append(functools.partial(_set, idx=idx, val=self._lst[idx]))
+        self._lst[idx] = val
+
+    def __delitem__(self, idx: int) -> None:
+        if idx < 0:
+            idx %= len(self)
+        self._undo.append(functools.partial(_ins, idx=idx, val=self._lst[idx]))
+        del self._lst[idx]
+
+    def insert(self, idx: int, val: str) -> None:
+        if idx < 0:
+            idx %= len(self)
+        self._undo.append(functools.partial(_del, idx=idx))
+        self._lst.insert(idx, val)
+
+    def undo(self, lst: MutableSequenceNoSlice) -> None:
+        for fn in reversed(self._undo):
+            fn(lst)
+
+    @property
+    def has_modifications(self) -> bool:
+        return bool(self._undo)
diff --git a/babi/main.py b/babi/main.py
index c03bb51..055e68c 100644
--- a/babi/main.py
+++ b/babi/main.py
@@ -19,7 +19,6 @@ from typing import cast
 from typing import Dict
 from typing import Generator
 from typing import IO
-from typing import Iterator
 from typing import List
 from typing import Match
 from typing import NamedTuple
@@ -27,14 +26,11 @@ from typing import Optional
 from typing import Pattern
 from typing import Sequence
 from typing import Tuple
-from typing import TYPE_CHECKING
 from typing import TypeVar
 from typing import Union
 
-if TYPE_CHECKING:
-    from typing import Protocol  # python3.8+
-else:
-    Protocol = object
+from babi.list_spy import ListSpy
+from babi.list_spy import MutableSequenceNoSlice
 
 VERSION_STR = 'babi v0'
 TCallable = TypeVar('TCallable', bound=Callable[..., Any])
@@ -100,77 +96,6 @@ def _scrolled_line(s: str, x: int, width: int) -> str:
         return s.ljust(width)
 
 
-class MutableSequenceNoSlice(Protocol):
-    def __len__(self) -> int: ...
-    def __getitem__(self, idx: int) -> str: ...
-    def __setitem__(self, idx: int, val: str) -> None: ...
-    def __delitem__(self, idx: int) -> None: ...
-    def insert(self, idx: int, val: str) -> None: ...
-
-    def __iter__(self) -> Iterator[str]:
-        for i in range(len(self)):
-            yield self[i]
-
-    def append(self, val: str) -> None:
-        self.insert(len(self), val)
-
-    def pop(self, idx: int = -1) -> str:
-        victim = self[idx]
-        del self[idx]
-        return victim
-
-
-def _del(lst: MutableSequenceNoSlice, *, idx: int) -> None:
-    del lst[idx]
-
-
-def _set(lst: MutableSequenceNoSlice, *, idx: int, val: str) -> None:
-    lst[idx] = val
-
-
-def _ins(lst: MutableSequenceNoSlice, *, idx: int, val: str) -> None:
-    lst.insert(idx, val)
-
-
-class ListSpy(MutableSequenceNoSlice):
-    def __init__(self, lst: MutableSequenceNoSlice) -> None:
-        self._lst = lst
-        self._undo: List[Callable[[MutableSequenceNoSlice], None]] = []
-
-    def __repr__(self) -> str:
-        return f'{type(self).__name__}({self._lst})'
-
-    def __len__(self) -> int:
-        return len(self._lst)
-
-    def __getitem__(self, idx: int) -> str:
-        return self._lst[idx]
-
-    def __setitem__(self, idx: int, val: str) -> None:
-        self._undo.append(functools.partial(_set, idx=idx, val=self._lst[idx]))
-        self._lst[idx] = val
-
-    def __delitem__(self, idx: int) -> None:
-        if idx < 0:
-            idx %= len(self)
-        self._undo.append(functools.partial(_ins, idx=idx, val=self._lst[idx]))
-        del self._lst[idx]
-
-    def insert(self, idx: int, val: str) -> None:
-        if idx < 0:
-            idx %= len(self)
-        self._undo.append(functools.partial(_del, idx=idx))
-        self._lst.insert(idx, val)
-
-    def undo(self, lst: MutableSequenceNoSlice) -> None:
-        for fn in reversed(self._undo):
-            fn(lst)
-
-    @property
-    def has_modifications(self) -> bool:
-        return bool(self._undo)
-
-
 class Key(NamedTuple):
     wch: Union[int, str]
     keyname: bytes
diff --git a/tests/list_spy_test.py b/tests/list_spy_test.py
index 2f9d135..51c985f 100644
--- a/tests/list_spy_test.py
+++ b/tests/list_spy_test.py
@@ -1,6 +1,6 @@
 import pytest
 
-from babi.main import ListSpy
+from babi.list_spy import ListSpy
 
 
 def test_list_spy_repr():