diff --git a/.gitignore b/.gitignore
index 2a0669d11a4..7fea4f3be3d 100644
--- a/.gitignore
+++ b/.gitignore
@@ -23,6 +23,9 @@ __pycache__
 _build
 rtd_docs/generated
 
+# API docs
+docs/api_docs
+
 # swap files
 *.swp
 
diff --git a/check/nbformat b/check/nbformat
index 19c6dcf6957..2a123c9ffb8 100755
--- a/check/nbformat
+++ b/check/nbformat
@@ -29,7 +29,7 @@ cd "$( cd "$( dirname "${BASH_SOURCE[0]}" )" && pwd )"
 cd "$(git rev-parse --show-toplevel)"
 
 # Install a pinned version of tf-docs
-TF_DOCS_COMMIT=ec2bfadbec885fc40268b4193d8b87648ab45791
+TF_DOCS_COMMIT=b3dc8a922d8bdc6e998a8ad4f4953359dc6e576a
 TF_DOCS_INSTALLED=$(pip list | grep  -c $TF_DOCS_COMMIT)
 
 if [ "$TF_DOCS_INSTALLED" != "1" ]; then
diff --git a/cirq/_doc.py b/cirq/_doc.py
index 1c370da239c..52043964b01 100644
--- a/cirq/_doc.py
+++ b/cirq/_doc.py
@@ -54,3 +54,33 @@ def document(value: Any, doc_string: str = ''):
         # print(traceback.format_stack(limit=2)[0])
         pass
     return value
+
+
+# This is based on
+# https://github.com/tensorflow/docs/commit/129e54b1a1dc2c2c82ad94bc81e986c7c2be3d6a#diff-85111596b523b2940651a8856939755c8531d470948895c7133deb6a537bc889R295-R324
+
+_DOC_PRIVATE = "_tf_docs_doc_private"
+
+
+def doc_private(obj):
+    """A decorator: Generates docs for private methods/functions.
+
+    For example:
+    ```
+    class Try:
+      @doc_private
+      def _private(self):
+        ...
+    ```
+    As a rule of thumb, private (beginning with `_`) methods/functions are
+    not documented. This decorator allows to force document a private
+    method/function.
+
+    Args:
+      obj: The class-attribute to force the documentation for.
+    Returns:
+      obj
+    """
+
+    setattr(obj, _DOC_PRIVATE, None)
+    return obj
diff --git a/cirq/experiments/qubit_characterizations.py b/cirq/experiments/qubit_characterizations.py
index 22fadd33f55..75e06b3ff36 100644
--- a/cirq/experiments/qubit_characterizations.py
+++ b/cirq/experiments/qubit_characterizations.py
@@ -445,34 +445,26 @@ def two_qubit_state_tomography(sampler: work.Sampler,
     The state probabilities $P_{00}, P_{01}, P_{10}$ thus obtained contribute
     to the following linear equations (setting $c_{00} = 1$):
 
-        $$
-        c_{03} + c_{30} + c_{33} = 4*P_{00} - 1
-        $$
-
-        $$
-        -c_{03} + c_{30} - c_{33} = 4*P_{01} - 1
-        $$
-
-        $$
-        c_{03} - c_{30} - c_{33} = 4*P_{10} - 1
-        $$
+    $$
+    \begin{align}
+    c_{03} + c_{30} + c_{33} &= 4*P_{00} - 1 \\
+    -c_{03} + c_{30} - c_{33} &= 4*P_{01} - 1 \\
+    c_{03} - c_{30} - c_{33} &= 4*P_{10} - 1
+    \end{align}
+    $$
 
     And if a Y/2 rotation is applied to the first qubit and a X/2 rotation
     is applied to the second qubit before measurement, the measurement
     operators are $(I -/+ \sigma_x) \bigotimes (I +/- \sigma_y)$. The
     probabilities obtained instead contribute to the following linear equations:
 
-        $$
-        c_{02} - c_{10} - c_{12} = 4*P_{00} - 1
-        $$
-
-        $$
-        -c_{02} - c_{10} + c_{12} = 4*P_{01} - 1
-        $$
-
-        $$
-        c_{02} + c_{10} + c_{12} = 4*P_{10} - 1
-        $$
+    $$
+    \begin{align}
+    c_{02} - c_{10} - c_{12} &= 4*P_{00} - 1 \\
+    -c_{02} - c_{10} + c_{12} &= 4*P_{01} - 1 \\
+    c_{02} + c_{10} + c_{12} &= 4*P_{10} - 1
+    \end{align}
+    $$
 
     Note that this set of equations has the same form as the first set under
     the transformation $c_{03}$ <-> $c_{02}, c_{30}$ <-> $-c_{10}$ and
diff --git a/cirq/protocols/act_on_protocol.py b/cirq/protocols/act_on_protocol.py
index 71fec022cf1..36493ed8b1f 100644
--- a/cirq/protocols/act_on_protocol.py
+++ b/cirq/protocols/act_on_protocol.py
@@ -17,7 +17,7 @@
 
 from typing_extensions import Protocol
 
-from cirq._doc import document
+from cirq._doc import doc_private
 from cirq.type_workarounds import NotImplementedType
 
 if TYPE_CHECKING:
@@ -27,7 +27,7 @@
 class SupportsActOn(Protocol):
     """An object that explicitly specifies how to act on simulator states."""
 
-    @document
+    @doc_private
     def _act_on_(self, args: Any) -> Union[NotImplementedType, bool]:
         """Applies an action to the given argument, if it is a supported type.
 
diff --git a/cirq/protocols/apply_channel_protocol.py b/cirq/protocols/apply_channel_protocol.py
index f1065c545ec..b0ebffc130d 100644
--- a/cirq/protocols/apply_channel_protocol.py
+++ b/cirq/protocols/apply_channel_protocol.py
@@ -19,6 +19,7 @@
 from typing_extensions import Protocol
 
 from cirq import linalg
+from cirq._doc import doc_private
 from cirq.protocols.apply_unitary_protocol import (
     apply_unitary,
     ApplyUnitaryArgs,
@@ -115,6 +116,7 @@ def __init__(self, target_tensor: np.ndarray, out_buffer: np.ndarray,
 class SupportsApplyChannel(Protocol):
     """An object that can efficiently implement a channel."""
 
+    @doc_private
     def _apply_channel_(self, args: ApplyChannelArgs
                        ) -> Union[np.ndarray, None, NotImplementedType]:
         """Efficiently applies a channel.
diff --git a/cirq/protocols/apply_mixture_protocol.py b/cirq/protocols/apply_mixture_protocol.py
index b537f968dad..0f05a352078 100644
--- a/cirq/protocols/apply_mixture_protocol.py
+++ b/cirq/protocols/apply_mixture_protocol.py
@@ -19,6 +19,7 @@
 from typing_extensions import Protocol
 
 from cirq import linalg
+from cirq._doc import doc_private
 from cirq.protocols.apply_unitary_protocol import (
     apply_unitary,
     ApplyUnitaryArgs,
@@ -112,6 +113,7 @@ def __init__(self,
 class SupportsApplyMixture(Protocol):
     """An object that can efficiently implement a mixture."""
 
+    @doc_private
     def _apply_mixture_(self, args: ApplyMixtureArgs
                        ) -> Union[np.ndarray, None, NotImplementedType]:
         """Efficiently applies a mixture.
diff --git a/cirq/protocols/apply_unitary_protocol.py b/cirq/protocols/apply_unitary_protocol.py
index 0ed9addfbe2..a1beface48b 100644
--- a/cirq/protocols/apply_unitary_protocol.py
+++ b/cirq/protocols/apply_unitary_protocol.py
@@ -29,6 +29,7 @@
 from typing_extensions import Protocol
 
 from cirq import linalg, qis
+from cirq._doc import doc_private
 from cirq.protocols import qid_shape_protocol
 from cirq.protocols.decompose_protocol import (
     _try_decompose_into_operations_and_qubits,)
@@ -219,6 +220,7 @@ def subspace_index(self,
 class SupportsConsistentApplyUnitary(Protocol):
     """An object that can be efficiently left-multiplied into tensors."""
 
+    @doc_private
     def _apply_unitary_(self, args: ApplyUnitaryArgs
                        ) -> Union[np.ndarray, None, NotImplementedType]:
         """Left-multiplies a unitary effect onto a tensor with good performance.
diff --git a/cirq/protocols/approximate_equality_protocol.py b/cirq/protocols/approximate_equality_protocol.py
index 8dae0e824e7..848a003399f 100644
--- a/cirq/protocols/approximate_equality_protocol.py
+++ b/cirq/protocols/approximate_equality_protocol.py
@@ -22,10 +22,13 @@
 
 from typing_extensions import Protocol
 
+from cirq._doc import doc_private
+
 
 class SupportsApproximateEquality(Protocol):
     """Object which can be compared approximately."""
 
+    @doc_private
     def _approx_eq_(self, other: Any, *, atol: Union[int, float]) -> bool:
         """Approximate comparator.
 
diff --git a/cirq/protocols/channel.py b/cirq/protocols/channel.py
index b4e411132d9..29e8b33cdf8 100644
--- a/cirq/protocols/channel.py
+++ b/cirq/protocols/channel.py
@@ -20,6 +20,7 @@
 import numpy as np
 from typing_extensions import Protocol
 
+from cirq._doc import doc_private
 from cirq.protocols.decompose_protocol import (
     _try_decompose_into_operations_and_qubits,)
 from cirq.protocols.mixture_protocol import has_mixture
@@ -42,6 +43,7 @@
 class SupportsChannel(Protocol):
     """An object that may be describable as a quantum channel."""
 
+    @doc_private
     def _channel_(self) -> Union[Sequence[np.ndarray], NotImplementedType]:
         r"""A list of matrices describing the quantum channel.
 
@@ -76,6 +78,8 @@ def _channel_(self) -> Union[Sequence[np.ndarray], NotImplementedType]:
             A list of matrices describing the channel (Kraus operators), or
             NotImplemented if there is no such matrix.
         """
+
+    @doc_private
     def _has_channel_(self) -> bool:
         """Whether this value has a channel representation.
 
diff --git a/cirq/protocols/circuit_diagram_info_protocol.py b/cirq/protocols/circuit_diagram_info_protocol.py
index 71d1f90f386..a118e67ea74 100644
--- a/cirq/protocols/circuit_diagram_info_protocol.py
+++ b/cirq/protocols/circuit_diagram_info_protocol.py
@@ -21,6 +21,7 @@
 from typing_extensions import Protocol
 
 from cirq import protocols, value
+from cirq._doc import doc_private
 
 if TYPE_CHECKING:
     import cirq
@@ -304,6 +305,7 @@ def with_args(self, **kwargs):
 class SupportsCircuitDiagramInfo(Protocol):
     """A diagrammable operation on qubits."""
 
+    @doc_private
     def _circuit_diagram_info_(
             self, args: CircuitDiagramInfoArgs
     ) -> Union[str, Iterable[str], CircuitDiagramInfo]:
diff --git a/cirq/protocols/commutes_protocol.py b/cirq/protocols/commutes_protocol.py
index 0802a2c5a43..b4a6e5cf5d0 100644
--- a/cirq/protocols/commutes_protocol.py
+++ b/cirq/protocols/commutes_protocol.py
@@ -16,11 +16,10 @@
 from typing import Any, TypeVar, Union
 
 import numpy as np
-
 from typing_extensions import Protocol
 
 from cirq import linalg, ops
-from cirq._doc import document
+from cirq._doc import doc_private
 from cirq.protocols import qid_shape_protocol, unitary_protocol
 from cirq.type_workarounds import NotImplementedType
 
@@ -36,7 +35,7 @@
 class SupportsCommutes(Protocol):
     """An object that can determine commutation relationships vs others."""
 
-    @document
+    @doc_private
     def _commutes_(self, other: Any,
                    atol: float) -> Union[None, bool, NotImplementedType]:
         r"""Determines if this object commutes with the other object.
diff --git a/cirq/protocols/decompose_protocol.py b/cirq/protocols/decompose_protocol.py
index 7c13614223f..3564d106ce2 100644
--- a/cirq/protocols/decompose_protocol.py
+++ b/cirq/protocols/decompose_protocol.py
@@ -27,9 +27,11 @@
     Union,
 )
 from collections import defaultdict
+
 from typing_extensions import Protocol
 
 from cirq import devices, ops
+from cirq._doc import doc_private
 from cirq.protocols import qid_shape_protocol
 from cirq.type_workarounds import NotImplementedType
 
@@ -92,6 +94,7 @@ class SupportsDecompose(Protocol):
     raise a caller-provided error.
     """
 
+    @doc_private
     def _decompose_(self) -> DecomposeResult:
         pass
 
diff --git a/cirq/protocols/equal_up_to_global_phase_protocol.py b/cirq/protocols/equal_up_to_global_phase_protocol.py
index 898569fe35f..3656e77bbd5 100644
--- a/cirq/protocols/equal_up_to_global_phase_protocol.py
+++ b/cirq/protocols/equal_up_to_global_phase_protocol.py
@@ -12,21 +12,22 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
-from collections.abc import Iterable
 import numbers
+from collections.abc import Iterable
 from typing import Any, Union
+
 import numpy as np
 from typing_extensions import Protocol
 
 from cirq import linalg
-from cirq._doc import document
+from cirq._doc import doc_private
 from cirq.protocols.approximate_equality_protocol import approx_eq
 
 
 class SupportsEqualUpToGlobalPhase(Protocol):
     """Object which can be compared for equality mod global phase."""
 
-    @document
+    @doc_private
     def _equal_up_to_global_phase_(self, other: Any, *,
                                    atol: Union[int, float]) -> bool:
         """Approximate comparator.
diff --git a/cirq/protocols/has_unitary_protocol.py b/cirq/protocols/has_unitary_protocol.py
index 048fb6959d3..edc3a3f0ca9 100644
--- a/cirq/protocols/has_unitary_protocol.py
+++ b/cirq/protocols/has_unitary_protocol.py
@@ -13,7 +13,6 @@
 # limitations under the License.
 
 from typing import (
-    TYPE_CHECKING,
     Any,
     TypeVar,
     Optional,
@@ -22,15 +21,12 @@
 import numpy as np
 from typing_extensions import Protocol
 
-from cirq._doc import document
+from cirq import qis
+from cirq._doc import doc_private
 from cirq.protocols import qid_shape_protocol
 from cirq.protocols.apply_unitary_protocol import ApplyUnitaryArgs
 from cirq.protocols.decompose_protocol import (
     _try_decompose_into_operations_and_qubits,)
-from cirq import qis
-
-if TYPE_CHECKING:
-    import cirq
 
 TDefault = TypeVar('TDefault')
 
@@ -38,7 +34,7 @@
 class SupportsExplicitHasUnitary(Protocol):
     """An object that explicitly specifies whether it has a unitary effect."""
 
-    @document
+    @doc_private
     def _has_unitary_(self) -> bool:
         """Determines whether the receiver has a unitary effect.
 
diff --git a/cirq/protocols/json_serialization.py b/cirq/protocols/json_serialization.py
index d395dcb9d03..9ea5aa690cb 100644
--- a/cirq/protocols/json_serialization.py
+++ b/cirq/protocols/json_serialization.py
@@ -35,6 +35,7 @@
 import sympy
 from typing_extensions import Protocol
 
+from cirq._doc import doc_private
 from cirq.ops import raw_types  # Tells mypy that the raw_types module exists
 from cirq.type_workarounds import NotImplementedType
 
@@ -245,6 +246,7 @@ class SupportsJSON(Protocol):
     constructor.
     """
 
+    @doc_private
     def _json_dict_(self) -> Union[None, NotImplementedType, Dict[Any, Any]]:
         pass
 
diff --git a/cirq/protocols/measurement_key_protocol.py b/cirq/protocols/measurement_key_protocol.py
index a8e91f32778..7284a5398a9 100644
--- a/cirq/protocols/measurement_key_protocol.py
+++ b/cirq/protocols/measurement_key_protocol.py
@@ -17,12 +17,10 @@
 
 from typing_extensions import Protocol
 
-from cirq._doc import document
-
+from cirq._doc import doc_private
 from cirq.protocols.decompose_protocol import \
     _try_decompose_into_operations_and_qubits
 
-
 # This is a special indicator value used by the inverse method to determine
 # whether or not the caller provided a 'default' argument.
 RaiseTypeErrorIfNotProvided = ([],)  # type: Any
@@ -49,7 +47,7 @@ class SupportsMeasurementKey(Protocol):
     conditional on the measurement outcome being $k$.
     """
 
-    @document
+    @doc_private
     def _measurement_key_(self) -> str:
         """Return the key that will be used to identify this measurement.
 
@@ -58,7 +56,7 @@ def _measurement_key_(self) -> str:
         will be stored.
         """
 
-    @document
+    @doc_private
     def _measurement_keys_(self) -> Iterable[str]:
         """Return the keys for measurements performed by the receiving object.
 
diff --git a/cirq/protocols/mixture_protocol.py b/cirq/protocols/mixture_protocol.py
index 52168126536..9cf77c9b5b5 100644
--- a/cirq/protocols/mixture_protocol.py
+++ b/cirq/protocols/mixture_protocol.py
@@ -19,11 +19,10 @@
 from typing_extensions import Protocol
 
 from cirq._compat import deprecated
-from cirq._doc import document
+from cirq._doc import doc_private
 from cirq.protocols.decompose_protocol import \
     _try_decompose_into_operations_and_qubits
 from cirq.protocols.has_unitary_protocol import has_unitary
-
 from cirq.type_workarounds import NotImplementedType
 
 # This is a special indicator value used by the inverse method to determine
@@ -35,7 +34,7 @@ class SupportsMixture(Protocol):
     """An object that decomposes into a probability distribution of unitaries.
     """
 
-    @document
+    @doc_private
     def _mixture_(self
                  ) -> Union[Sequence[Tuple[float, Any]], NotImplementedType]:
         """Decompose into a probability distribution of unitaries.
@@ -53,7 +52,7 @@ def _mixture_(self
             A list of (probability, unitary) pairs.
         """
 
-    @document
+    @doc_private
     def _has_mixture_(self) -> bool:
         """Whether this value has a mixture representation.
 
diff --git a/cirq/protocols/pauli_expansion_protocol.py b/cirq/protocols/pauli_expansion_protocol.py
index d5323a88fb4..23b57830dd0 100644
--- a/cirq/protocols/pauli_expansion_protocol.py
+++ b/cirq/protocols/pauli_expansion_protocol.py
@@ -17,6 +17,7 @@
 from typing_extensions import Protocol
 
 from cirq import value
+from cirq._doc import doc_private
 from cirq.linalg import operator_spaces
 from cirq.protocols import qid_shape_protocol, unitary_protocol
 
@@ -29,6 +30,7 @@
 class SupportsPauliExpansion(Protocol):
     """An object that knows its expansion in the Pauli basis."""
 
+    @doc_private
     def _pauli_expansion_(self) -> value.LinearDict[str]:
         """Efficiently obtains expansion of self in the Pauli basis.
 
diff --git a/cirq/protocols/phase_protocol.py b/cirq/protocols/phase_protocol.py
index f7b6310290e..e1f51bd63ba 100644
--- a/cirq/protocols/phase_protocol.py
+++ b/cirq/protocols/phase_protocol.py
@@ -19,7 +19,7 @@
 # This is a special value to indicate that a type error should be returned.
 # This is used within phase_by to raise an error if no underlying
 # implementation of _phase_by_ exists.
-from cirq._doc import document
+from cirq._doc import doc_private
 
 RaiseTypeErrorIfNotProvided = ([],)  # type: Any
 
@@ -29,7 +29,7 @@
 class SupportsPhase(Protocol):
     """An effect that can be phased around the Z axis of target qubits."""
 
-    @document
+    @doc_private
     def _phase_by_(self: Any, phase_turns: float, qubit_index: int):
         """Returns a phased version of the effect.
 
diff --git a/cirq/protocols/qasm.py b/cirq/protocols/qasm.py
index 7f8f1d0f530..e9a45a40b5b 100644
--- a/cirq/protocols/qasm.py
+++ b/cirq/protocols/qasm.py
@@ -19,7 +19,7 @@
 from typing_extensions import Protocol
 
 from cirq import ops
-from cirq._doc import document
+from cirq._doc import doc_private
 from cirq.type_workarounds import NotImplementedType
 
 if TYPE_CHECKING:
@@ -82,7 +82,7 @@ class SupportsQasm(Protocol):
     will be used instead.
     """
 
-    @document
+    @doc_private
     def _qasm_(self) -> Union[None, NotImplementedType, str]:
         pass
 
@@ -95,7 +95,7 @@ class SupportsQasmWithArgs(Protocol):
     will be used instead.
     """
 
-    @document
+    @doc_private
     def _qasm_(self,
                args: QasmArgs) -> Union[None, NotImplementedType, str]:
         pass
@@ -109,7 +109,7 @@ class SupportsQasmWithArgsAndQubits(Protocol):
     will be used instead.
     """
 
-    @document
+    @doc_private
     def _qasm_(self,
                qubits: Tuple['cirq.Qid'],
                args: QasmArgs) -> Union[None, NotImplementedType, str]:
diff --git a/cirq/protocols/qid_shape_protocol.py b/cirq/protocols/qid_shape_protocol.py
index c6c5ce05827..0137aed6257 100644
--- a/cirq/protocols/qid_shape_protocol.py
+++ b/cirq/protocols/qid_shape_protocol.py
@@ -12,17 +12,14 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
-from typing import TYPE_CHECKING, Any, Sequence, Tuple, TypeVar, Union
+from typing import Any, Sequence, Tuple, TypeVar, Union
 
 from typing_extensions import Protocol
 
 from cirq import ops
-from cirq._doc import document
+from cirq._doc import document, doc_private
 from cirq.type_workarounds import NotImplementedType
 
-if TYPE_CHECKING:
-    import cirq
-
 # This is a special indicator value used by the methods to determine whether or
 # not the caller provided a 'default' argument. It must be of type
 # Tuple[int, ...] to ensure the method has the correct type signature in that
@@ -39,7 +36,7 @@ class SupportsExplicitQidShape(Protocol):
     """A unitary, channel, mixture or other object that operates on a known
     number qubits/qudits/qids, each with a specific number of quantum levels."""
 
-    @document
+    @doc_private
     def _qid_shape_(self) -> Union[Tuple[int, ...], NotImplementedType]:
         """A tuple specifying the number of quantum levels of each qid this
         object operates on, e.g. (2, 2, 2) for a three-qubit gate.
diff --git a/cirq/protocols/resolve_parameters.py b/cirq/protocols/resolve_parameters.py
index 70622e74560..c287c7c0748 100644
--- a/cirq/protocols/resolve_parameters.py
+++ b/cirq/protocols/resolve_parameters.py
@@ -14,12 +14,12 @@
 
 import numbers
 from typing import AbstractSet, Any, TypeVar, TYPE_CHECKING
-from typing_extensions import Protocol
 
 import sympy
+from typing_extensions import Protocol
 
 from cirq import study
-from cirq._doc import document
+from cirq._doc import doc_private
 
 if TYPE_CHECKING:
     import cirq
@@ -31,13 +31,13 @@ class SupportsParameterization(Protocol):
     """An object that can be parameterized by Symbols and resolved
     via a ParamResolver"""
 
-    @document
+    @doc_private
     def _is_parameterized_(self: Any) -> bool:
         """Whether the object is parameterized by any Symbols that require
         resolution. Returns True if the object has any unresolved Symbols
         and False otherwise."""
 
-    @document
+    @doc_private
     def _parameter_names_(self: Any) -> AbstractSet[str]:
         """Returns a collection of string names of parameters that require
         resolution. If _is_parameterized_ is False, the collection is empty.
@@ -46,7 +46,7 @@ def _parameter_names_(self: Any) -> AbstractSet[str]:
         need to be evaluated, but no free symbols.
         """
 
-    @document
+    @doc_private
     def _resolve_parameters_(self: Any, param_resolver: 'cirq.ParamResolver'):
         """Resolve the parameters in the effect."""
 
diff --git a/cirq/protocols/trace_distance_bound.py b/cirq/protocols/trace_distance_bound.py
index c2909c5de7d..b9b9a4763a4 100644
--- a/cirq/protocols/trace_distance_bound.py
+++ b/cirq/protocols/trace_distance_bound.py
@@ -13,13 +13,13 @@
 # limitations under the License.
 
 from typing import Any, TypeVar, Optional, Sequence
+
 import numpy as np
 from typing_extensions import Protocol
 
-from cirq._doc import document
+from cirq._doc import doc_private
 from cirq.protocols import unitary_protocol
 
-
 TDefault = TypeVar('TDefault')
 
 
@@ -32,7 +32,7 @@ class SupportsTraceDistanceBound(Protocol):
     negligible.
     """
 
-    @document
+    @doc_private
     def _trace_distance_bound_(self) -> float:
         """A maximum on the trace distance between `val`'s input and output.
 
diff --git a/cirq/protocols/unitary_protocol.py b/cirq/protocols/unitary_protocol.py
index ee08545c593..2cf1be3683a 100644
--- a/cirq/protocols/unitary_protocol.py
+++ b/cirq/protocols/unitary_protocol.py
@@ -13,7 +13,6 @@
 # limitations under the License.
 
 from typing import (
-    TYPE_CHECKING,
     Any,
     TypeVar,
     Union,
@@ -24,7 +23,7 @@
 from typing_extensions import Protocol
 
 from cirq import qis
-from cirq._doc import document
+from cirq._doc import doc_private
 from cirq.protocols import qid_shape_protocol
 from cirq.protocols.apply_unitary_protocol import (
     ApplyUnitaryArgs,
@@ -34,9 +33,6 @@
     _try_decompose_into_operations_and_qubits,)
 from cirq.type_workarounds import NotImplementedType
 
-if TYPE_CHECKING:
-    import cirq
-
 # This is a special indicator value used by the unitary method to determine
 # whether or not the caller provided a 'default' argument. It must be of type
 # np.ndarray to ensure the method has the correct type signature in that case.
@@ -50,7 +46,7 @@
 class SupportsUnitary(Protocol):
     """An object that may be describable by a unitary matrix."""
 
-    @document
+    @doc_private
     def _unitary_(self) -> Union[np.ndarray, NotImplementedType]:
         """A unitary matrix describing this value, e.g. the matrix of a gate.
 
@@ -75,7 +71,7 @@ def _unitary_(self) -> Union[np.ndarray, NotImplementedType]:
             is no such matrix.
         """
 
-    @document
+    @doc_private
     def _has_unitary_(self) -> bool:
         """Whether this value has a unitary matrix representation.
 
diff --git a/dev_tools/docs/Dockerfile b/dev_tools/docs/Dockerfile
new file mode 100644
index 00000000000..f94bfce9317
--- /dev/null
+++ b/dev_tools/docs/Dockerfile
@@ -0,0 +1,44 @@
+# Copyright 2020 The Cirq Developers
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     https://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+########################################################################################
+# This is a Dockerfile to preview the api-docs generation
+#
+# Usage:
+#     docker build -t cirq-api-docs -f dev_tools/docs/Dockerfile .
+#     docker run -d --name=cirq-api-docs -p 8080:8080 cirq-api-docs
+# To stop:
+#     docker kill cirq-api-docs && docker rm cirq-api-docs
+#
+# You can then preview the site at http://localhost:8080
+# Eventually this might become the basis of an automated preview service for each
+# PR.
+########################################################################################
+
+FROM nikolaik/python-nodejs:python3.7-nodejs14
+
+RUN pip install -U git+https://github.com/tensorflow/docs && npm i -g markserv
+
+RUN mkdir /cirq
+
+WORKDIR /cirq
+
+ADD requirements.txt .
+RUN pip install -r requirements.txt
+
+ADD . /cirq
+RUN PYTHONPATH=/cirq python3 dev_tools/docs/build_api_docs.py --output_dir=docs/api_docs
+
+WORKDIR /cirq/docs/api_docs
+CMD ["markserv", "-b=false", "-p=8080", "-a=0.0.0.0"]
\ No newline at end of file