diff --git a/mypyc/doc/conf.py b/mypyc/doc/conf.py
index fdd98c12a221d..e6b2bfaf77b76 100644
--- a/mypyc/doc/conf.py
+++ b/mypyc/doc/conf.py
@@ -36,7 +36,9 @@
 # Add any Sphinx extension module names here, as strings. They can be
 # extensions coming with Sphinx (named 'sphinx.ext.*') or your custom
 # ones.
-extensions: list[str] = []
+extensions = ["sphinx.ext.intersphinx"]
+
+intersphinx_mapping = {"python": ("https://docs.python.org/3", None)}
 
 # Add any paths that contain templates here, relative to this directory.
 templates_path = ["_templates"]
diff --git a/mypyc/doc/index.rst b/mypyc/doc/index.rst
index 85e7b2808b210..fe683c4188f20 100644
--- a/mypyc/doc/index.rst
+++ b/mypyc/doc/index.rst
@@ -33,6 +33,7 @@ generate fast code.
 
    librt
    librt_base64
+   librt_strings
    librt_time
 
 .. toctree::
diff --git a/mypyc/doc/librt.rst b/mypyc/doc/librt.rst
index e418b5356ff61..f18cc93c80294 100644
--- a/mypyc/doc/librt.rst
+++ b/mypyc/doc/librt.rst
@@ -3,7 +3,7 @@
 Librt overview
 ==============
 
-The `librt <https://pypi.org/project/librt/>`_ package defines fast
+The `librt <https://pypi.org/project/librt/>`__ package defines fast
 primitive operations that are optimized for code compiled
 using mypyc. It has carefully selected efficient alternatives for
 certain Python standard library features.
@@ -26,6 +26,8 @@ Follow submodule links in the table to a detailed description of each submodule.
      - Description
    * - :doc:`librt.base64 <librt_base64>`
      - Fast Base64 encoding and decoding
+   * - :doc:`librt.strings <librt_strings>`
+     - String and bytes utilities
    * - :doc:`librt.time <librt_time>`
      - Time utilities
 
diff --git a/mypyc/doc/librt_strings.rst b/mypyc/doc/librt_strings.rst
new file mode 100644
index 0000000000000..1213f39623d61
--- /dev/null
+++ b/mypyc/doc/librt_strings.rst
@@ -0,0 +1,204 @@
+.. _librt-strings:
+
+librt.strings
+=============
+
+The ``librt.strings`` module is part of the ``librt`` package on PyPI, and it includes
+low-level string and bytes utilities.
+
+Classes
+-------
+
+BytesWriter
+^^^^^^^^^^^
+
+.. class:: BytesWriter
+
+   This class can be used to efficiently construct a bytes object from individual byte values
+   and from bytes or bytearray objects. It also provides some operations for accessing
+   and modifying items, but it doesn't support the full sequence interface.
+
+   This can be used as a faster replacement for :py:class:`io.BytesIO` or :py:class:`bytearray` in
+   compiled code. This is also usually faster than constructing a list of bytes objects and using
+   the :meth:`bytes.join` method to concatenate them.
+
+   .. method:: append(x: int, /) -> None
+
+      Append a byte to contents.
+
+   .. method:: write(b: bytes | bytearray, /) -> None
+
+      Append a bytes or bytearray object to contents.
+
+   .. method:: getvalue() -> bytes
+
+      Return the contents as a bytes object.
+
+   .. method:: truncate(size: i64, /) -> None
+
+      Truncate the length of the contents to the given size.
+
+   .. describe:: len(writer) → i64
+
+      Return the length of the contents.
+
+   .. describe:: writer[i] → u8
+
+      Return the byte at a specific index. The index can be negative.
+
+   .. describe:: writer[i] = x
+
+      Set a byte at a specific index. The index can be negative.
+
+.. _librt-string-writer:
+
+StringWriter
+^^^^^^^^^^^^
+
+.. class:: StringWriter
+
+   This class can be used to efficiently construct a string object from individual Unicode code
+   point integer values and from string objects. It also provides some operations for accessing
+   items, but it doesn't support the full sequence interface.
+
+   ``StringWriter`` can be used as a faster replacement for :py:class:`io.StringIO` in
+   compiled code. This is also usually faster than constructing a list of str objects and using
+   the :meth:`str.join` method to concatenate them.
+
+   If you construct a string from individual characters or code points, using integer values
+   can be much faster than using 1-length strings. You can rely on expressions like ``ord("x")``
+   being treated as compile-time integer constants in compiled code. Also ``ord(s[i])`` is
+   guaranteed to be a very quick operation in compiled code, if ``s`` has type :py:class:`str`.
+
+   .. method:: append(x: int, /) -> None
+
+      Append a Unicode code point (often representing a character) to the contents.
+
+   .. method:: write(s: str, /) -> None
+
+      Append a string to contents.
+
+   .. method:: getvalue() -> str
+
+      Return the contents as a string.
+
+   .. describe:: len(writer) → i64
+
+      Return the length of the contents (number of code points).
+
+   .. describe:: writer[i] → i32
+
+      Return the Unicode code point at a specific index as an integer. The index can be negative.
+
+Functions
+---------
+
+The ``write_*`` and ``read_*`` functions allow interpreting bytes as packed binary
+data. They can be used as (much) more efficient but lower-level alternatives to the
+stdlib :mod:`struct` module in compiled code.
+
+There are no functions for reading or writing individual bytes. ``BytesWriter.append`` can
+be used to insert a byte value, and ``b[n]`` can be used to read a byte value. Both
+are fast operations in compiled code.
+
+This example writes two binary values and reads them afterwards::
+
+    def example() -> None:
+        b = BytesWriter()
+        write_i32_le(b, 123)
+        write_f64_le(b, 4.5)
+        data = b.getvalue()
+
+        x = read_i32_le(data, 0)
+        y = read_f64_le(data, 4)
+        ...
+
+.. function:: write_i16_le(b: BytesWriter, n: i16, /) -> None
+
+   Append a 16-bit integer as a little-endian binary value.
+
+.. function:: write_i16_be(b: BytesWriter, n: i16, /) -> None
+
+   Append a 16-bit integer as a big-endian binary value.
+
+.. function:: read_i16_le(b: bytes, index: i64, /) -> i16
+
+   Read a 16-bit integer value starting at the given index as a little-endian binary value
+   (2 bytes).
+
+.. function:: read_i16_be(b: bytes, index: i64, /) -> i16
+
+   Read a 16-bit integer value starting at the given index as a big-endian binary value
+   (2 bytes).
+
+.. function:: write_i32_le(b: BytesWriter, n: i32, /) -> None
+
+   Append a 32-bit integer as a little-endian binary value.
+
+.. function:: write_i32_be(b: BytesWriter, n: i32, /) -> None
+
+   Append a 32-bit integer as a big-endian binary value.
+
+.. function:: read_i32_le(b: bytes, index: i64, /) -> i32
+
+   Read a 32-bit integer value starting at the given index as a little-endian binary value
+   (4 bytes).
+
+.. function:: read_i32_be(b: bytes, index: i64, /) -> i32
+
+   Read a 32-bit integer value starting at the given index as a big-endian binary value
+   (4 bytes).
+
+.. function:: write_i64_le(b: BytesWriter, n: i64, /) -> None
+
+   Append a 64-bit integer as a little-endian binary value.
+
+.. function:: write_i64_be(b: BytesWriter, n: i64, /) -> None
+
+   Append a 64-bit integer as a big-endian binary value.
+
+.. function:: read_i64_le(b: bytes, index: i64, /) -> i64
+
+   Read a 64-bit integer value starting at the given index as a little-endian binary value
+   (8 bytes).
+
+.. function:: read_i64_be(b: bytes, index: i64, /) -> i64
+
+   Read a 64-bit integer value starting at the given index as a big-endian binary value
+   (8 bytes).
+
+.. function:: write_f32_le(b: BytesWriter, n: float, /) -> None
+
+   Append a 32-bit floating-point value as a little-endian binary value.
+
+.. function:: write_f32_be(b: BytesWriter, n: float, /) -> None
+
+   Append a 32-bit floating-point value as a big-endian binary value.
+
+.. function:: read_f32_le(b: bytes, index: i64, /) -> float
+
+   Read a 32-bit floating-point value starting at the given index as a little-endian binary value
+   (4 bytes).
+
+.. function:: read_f32_be(b: bytes, index: i64, /) -> float
+
+   Read a 32-bit floating-point value starting at the given index as a big-endian binary value
+   (4 bytes).
+
+.. function:: write_f64_le(b: BytesWriter, n: float, /) -> None
+
+   Append a 64-bit floating-point value as a little-endian binary value.
+
+.. function:: write_f64_be(b: BytesWriter, n: float, /) -> None
+
+   Append a 64-bit floating-point value as a big-endian binary value.
+
+.. function:: read_f64_le(b: bytes, index: i64, /) -> float
+
+   Read a 64-bit floating-point value starting at the given index as a little-endian binary value
+   (8 bytes).
+
+.. function:: read_f64_be(b: bytes, index: i64, /) -> float
+
+   Read a 64-bit floating-point value starting at the given index as a big-endian binary value
+   (8 bytes).
diff --git a/mypyc/doc/str_operations.rst b/mypyc/doc/str_operations.rst
index 443e90a71bc7a..8f2daba02b72d 100644
--- a/mypyc/doc/str_operations.rst
+++ b/mypyc/doc/str_operations.rst
@@ -15,6 +15,11 @@ Construction
 * ``repr(x: int)``
 * ``repr(x: object)``
 
+.. note::
+
+    :ref:`librt.strings.StringWriter <librt-string-writer>` can be used to efficiently
+    construct strings in compiled code.
+
 Operators
 ---------
 
@@ -89,3 +94,6 @@ Functions
 
 * ``len(s: str)``
 * ``ord(s: str)``
+
+  * Calls with a literal argument are treated as compile-time integer constants (e.g.
+    ``ord("A")`` is equivalent to 65).