diff --git a/python/ffsim/protocols/approximate_equality.py b/python/ffsim/protocols/approximate_equality.py
index 711186343..758d2fbee 100644
--- a/python/ffsim/protocols/approximate_equality.py
+++ b/python/ffsim/protocols/approximate_equality.py
@@ -38,7 +38,23 @@ def _approx_eq_(self, other: Any, rtol: float, atol: float) -> bool:
 
 
 def approx_eq(obj: Any, other: Any, rtol: float = 1e-5, atol: float = 1e-8) -> bool:
-    """Return whether two objects are approximately equal."""
+    """Return whether two objects are approximately equal.
+
+    See the documentation of `np.isclose`_ for the interpretation of the tolerance
+    parameters ``rtol`` and ``atol``.
+
+    Args:
+        obj: The first object.
+        other: The object to compare to.
+        rtol: Relative numerical tolerance.
+        atol: Absolute numerical tolerance.
+
+    Returns:
+        True if the objects are approximately equal up to the specified tolerance,
+        and False otherwise.
+
+    .. _np.isclose: https://numpy.org/doc/stable/reference/generated/numpy.isclose.html
+    """
     method = getattr(obj, "_approx_eq_", None)
     if method is not None:
         return method(other, rtol=rtol, atol=atol)
diff --git a/python/ffsim/protocols/linear_operator.py b/python/ffsim/protocols/linear_operator.py
index ead426f7f..d50a591f4 100644
--- a/python/ffsim/protocols/linear_operator.py
+++ b/python/ffsim/protocols/linear_operator.py
@@ -38,7 +38,16 @@ def _linear_operator_(self, norb: int, nelec: tuple[int, int]) -> LinearOperator
 
 
 def linear_operator(obj: Any, norb: int, nelec: tuple[int, int]) -> LinearOperator:
-    """Return a SciPy LinearOperator representing the object."""
+    """Return a SciPy LinearOperator representing the object.
+
+    Args:
+        obj: The object to convert to a LinearOperator.
+        norb: The number of spatial orbitals.
+        nelec: The number of alpha and beta electrons.
+
+    Returns:
+        A Scipy LinearOperator representing the object.
+    """
     if isinstance(obj, FermionOperator):
         return _fermion_operator_to_linear_operator(obj, norb=norb, nelec=nelec)