diff --git a/requirements-test-latest.txt b/requirements-test-latest.txt
index ae1c0c3..b15f804 100644
--- a/requirements-test-latest.txt
+++ b/requirements-test-latest.txt
@@ -1,3 +1,5 @@
 # Newest published fixtures: Home Assistant 2026.2.3; requires Python 3.13.
 # Update together with the README's tested-versions note.
 pytest-homeassistant-custom-component==0.13.316
+# Bug-finding lint (see ruff.toml).
+ruff==0.14.0
diff --git a/requirements-test.txt b/requirements-test.txt
index 29e3dfa..26d5dce 100644
--- a/requirements-test.txt
+++ b/requirements-test.txt
@@ -2,3 +2,5 @@
 pytest-homeassistant-custom-component==0.13.298
 # aiodns 3.5 (HA's pin) uses APIs removed in pycares 5.
 pycares==4.11.0
+# Bug-finding lint (see ruff.toml).
+ruff==0.14.0
diff --git a/ruff.toml b/ruff.toml
new file mode 100644
index 0000000..4c86e83
--- /dev/null
+++ b/ruff.toml
@@ -0,0 +1,6 @@
+# Bug-finding lint only (pyflakes, syntax errors, bugbear); no style rules.
+# py39: the offline tests also run on older Pythons, so e.g. zip(strict=) is not available.
+target-version = "py39"
+
+[lint]
+select = ["F", "E9", "B"]
diff --git a/scripts/check.sh b/scripts/check.sh
index 0708bdb..2ff3315 100644
--- a/scripts/check.sh
+++ b/scripts/check.sh
@@ -4,6 +4,7 @@ set -eu
 # A transitive HA test dependency otherwise fetches metadata on import.
 export LITELLM_LOCAL_MODEL_COST_MAP=True
 python -m pip check
+python -m ruff check --no-cache .
 python -m unittest discover -s tests -v
 python -m pytest tests/ha -q
 python -m compileall -q custom_components/heating_mpc