diff --git a/.gitignore b/.gitignore
index 3306f6b..6dc3315 100644
--- a/.gitignore
+++ b/.gitignore
@@ -15,3 +15,5 @@ coverage.xml
 .dmypy.json
 .hypothesis/
 .idea/
+.codspeed
+uv.lock
diff --git a/pyproject.toml b/pyproject.toml
index 105017d..c59fe25 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -83,6 +83,7 @@ allow_untyped_defs = false
 # Allow test functions to be untyped
 module = "tests.*"
 allow_untyped_defs = true
+disallow_untyped_calls = false
 
 [tool.pylint.MASTER]
 persistent = "no"
diff --git a/tests/test_benchmark_http.py b/tests/test_benchmark_http.py
new file mode 100644
index 0000000..f578832
--- /dev/null
+++ b/tests/test_benchmark_http.py
@@ -0,0 +1,60 @@
+from collections import OrderedDict
+
+import pytest
+
+from w3lib.http import headers_dict_to_raw, headers_raw_to_dict
+
+pytest.importorskip("pytest_codspeed", reason="Benchmark tests require pytest-codspeed")
+
+pytestmark = pytest.mark.benchmark
+
+
+def _header_case_long_headers():
+    dct = OrderedDict(
+        [
+            (b"X-Custom-Header", [b"a" * 1_000]),
+            (b"X-Custom-Header-2", [b"b" * 1_000]),
+        ]
+    )
+    raw = (
+        b"X-Custom-Header: " + b"a" * 1_000 + b"\r\n"
+        b"X-Custom-Header-2: " + b"b" * 1_000
+    )  # fmt: off
+    return "long_headers", dct, raw
+
+
+def _header_case_many_unique_headers():
+    dct = OrderedDict(
+        [(f"Header-{i}".encode(), [f"value-{i}".encode()]) for i in range(100)]
+    )
+    raw = b"\r\n".join([f"Header-{i}: value-{i}".encode() for i in range(100)])
+    return "many_unique_headers", dct, raw
+
+
+def _header_case_many_repeated_headers():
+    values = [f"id={i}".encode() for i in range(100)]
+    dct = OrderedDict([(b"Set-Cookie", values)])
+    raw = b"\r\n".join([b"Set-Cookie: " + val for val in values])
+    return "many_repeated_headers", dct, raw
+
+
+header_cases = [
+    _header_case_long_headers(),
+    _header_case_many_unique_headers(),
+    _header_case_many_repeated_headers(),
+]
+
+
+@pytest.mark.parametrize(
+    ("_id", "dct", "raw"),
+    header_cases,
+    ids=[case[0] for case in header_cases],
+)
+class TestBenchmarkHttp:
+    def test_bench_dict_to_raw(self, benchmark, _id, dct, raw):  # noqa: PT019
+        result = benchmark(lambda: headers_dict_to_raw(dct))
+        assert result == raw
+
+    def test_bench_raw_to_dict(self, benchmark, _id, dct, raw):  # noqa: PT019
+        result = benchmark(lambda: headers_raw_to_dict(raw))
+        assert result == dct
diff --git a/tests/test_http.py b/tests/test_http.py
index e0ece39..a212c65 100644
--- a/tests/test_http.py
+++ b/tests/test_http.py
@@ -55,7 +55,10 @@ def test_headers_dict_to_raw(self):
 
     def test_headers_dict_to_raw_listtuple(self):
         dct: HeadersDictInput = OrderedDict(
-            [(b"Content-type", [b"text/html"]), (b"Accept", [b"gzip"])]
+            [
+                (b"Content-type", [b"text/html"]),
+                (b"Accept", [b"gzip"]),
+            ]
         )
         assert headers_dict_to_raw(dct) == b"Content-type: text/html\r\nAccept: gzip"
 
diff --git a/tox.ini b/tox.ini
index 9a2de58..4e092dd 100644
--- a/tox.ini
+++ b/tox.ini
@@ -4,7 +4,20 @@
 # and then run "tox" from this directory.
 
 [tox]
-envlist = py39, py310, py311, py312, py313, py314, pypy3.10, pypy3.11, docs, pylint, typing, pre-commit, twinecheck
+envlist =
+    py39
+    py310
+    py311
+    py312
+    py313
+    py314
+    pypy3.10
+    pypy3.11
+    docs
+    pylint
+    typing
+    pre-commit
+    twinecheck
 
 [testenv]
 deps =
@@ -51,3 +64,23 @@ deps =
 commands =
     python -m build --sdist
     twine check dist/*
+
+[testenv:benchmark-{py39,py310,py311,py312,py313,py314,pypy310,pypy311}]
+basepython =
+    py39: python3.9
+    py310: python3.10
+    py311: python3.11
+    py312: python3.12
+    py313: python3.13
+    py314: python3.14
+    pypy310: pypy3.10
+    pypy311: pypy3.11
+deps =
+    pytest
+    pytest-codspeed
+commands =
+    python -m pytest \
+        --codspeed \
+        --codspeed-warmup-time=1 \
+        --codspeed-max-rounds=10000 \
+        --codspeed-max-time=10