diff --git a/.github/workflows/pre-commit.yml b/.github/workflows/pre-commit.yml
index 964fb5abc..2bd0cc133 100644
--- a/.github/workflows/pre-commit.yml
+++ b/.github/workflows/pre-commit.yml
@@ -24,3 +24,9 @@ jobs:
           python-version: "3.12"
           cache: 'pip'
       - uses: pre-commit/action@v3.0.1
+        # Don't run the pytest mark check against everything in the CI
+        # for now since a lot of files are still missing them. This check
+        # is used to help contributors remember to add the marks when they
+        # commit.
+        env:
+          SKIP: check-test-ci-coverage
diff --git a/.pre-commit-config.yaml b/.pre-commit-config.yaml
index 6db093e0e..be649785d 100644
--- a/.pre-commit-config.yaml
+++ b/.pre-commit-config.yaml
@@ -54,6 +54,13 @@ repos:
       verbose: true
       stages: [commit-msg]
 
+    - id: check-test-ci-coverage
+      name: Ensure test files have pytestmarks
+      entry: python tools/pre_commit/check_test_marks.py
+      language: python
+      types: [python]
+      files: ^tests/
+
     # Keep `suggestion` last
     - id: suggestion
       name: Suggestion
diff --git a/tools/pre_commit/check_test_marks.py b/tools/pre_commit/check_test_marks.py
new file mode 100644
index 000000000..9a727ab72
--- /dev/null
+++ b/tools/pre_commit/check_test_marks.py
@@ -0,0 +1,111 @@
+#!/usr/bin/env python3
+# SPDX-License-Identifier: Apache-2.0
+# SPDX-FileCopyrightText: Copyright contributors to the vLLM project
+"""Run a pre-commit hook that fails if test files are modified or added
+that (probably) never run in the CI. For now, this means that every tests file
+needs to have a CI level marker (e.g., core_model, advanced_model, full_model,
+etc) and hardware mark / helper so that we ensure mutated tests will actually
+be selected as long as there are pytest commands pointing at the right paths.
+"""
+
+import os
+import re
+import sys
+
+# CI level markers
+LEVEL_MARKERS = ("core_model", "advanced_model", "full_model", "slow")
+
+# Hardware markers. These are platforms and resources that CI filters on.
+# NOTE: If new hardware marks are added to pyproject.toml etc, we need
+# to add them here as well.
+HARDWARE_MARKERS = (
+    "cpu",
+    "gpu",
+    "cuda",
+    "rocm",
+    "xpu",
+    "npu",
+    "musa",
+    "H100",
+    "L4",
+    "MI325",
+    "B60",
+    "S5000",
+    "A2",
+    "A3",
+)
+
+# Helpers from tests/helpers/mark.py that auto-apply hardware marks.
+HARDWARE_HELPERS = ("hardware_test", "hardware_marks")
+
+# Match mark.X since we could also do `from pytest import mark`.
+# \b prevents matching prefixes (e.g., mark.slow vs mark.slow_test).
+LEVEL_RE = re.compile(r"mark\.(?:" + "|".join(LEVEL_MARKERS) + r")\b")
+HARDWARE_RE = re.compile(r"mark\.(?:" + "|".join(HARDWARE_MARKERS) + r")\b")
+HELPER_RE = re.compile(r"(?:" + "|".join(HARDWARE_HELPERS) + r")\s*\(")
+
+MISSING_LEVEL_MARKER = "Level"
+MISSING_HARDWARE_MARKER = "Hardware"
+
+# Check if a file is located under tests/ and matches test_<something>.py
+# or <something>_test.py, since pytest technically collects on both.
+# Note that we use the former everywhere in this repo by convention.
+TEST_FILE_RE = re.compile(r"^tests/(?:.*/)?(?:test_[^/]*\.py$|[^/]*_test\.py$)")
+
+
+def is_test_file(path: str) -> bool:
+    """Determine whether or not a path is pointing at a test file or not."""
+    return bool(TEST_FILE_RE.match(path))
+
+
+def read_test_file(path: str) -> str | None:
+    """Read a test file's contents, or return None if it doesn't exist."""
+    if not os.path.isfile(path):
+        return None
+    with open(path, encoding="utf-8") as f:
+        return f.read()
+
+
+def has_level_marker(contents: str) -> bool:
+    """Check if file contents contain at least one CI level marker."""
+    return bool(LEVEL_RE.search(contents))
+
+
+def has_hardware_marker(contents: str) -> bool:
+    """Check if file contents contain any hardware marker or helpers."""
+    return bool(HARDWARE_RE.search(contents) or HELPER_RE.search(contents))
+
+
+def get_files_missing_markers(
+    staged_files: list[str],
+) -> dict[str, list[str]]:
+    """Return a dict mapping file path to list of missing marker types."""
+    results: dict[str, list[str]] = {}
+    for path in staged_files:
+        if is_test_file(path) and (contents := read_test_file(path)) is not None:
+            missing = []
+            if not has_level_marker(contents):
+                missing.append(MISSING_LEVEL_MARKER)
+            if not has_hardware_marker(contents):
+                missing.append(MISSING_HARDWARE_MARKER)
+            if missing:
+                results[path] = missing
+    return results
+
+
+if __name__ == "__main__":
+    missing = get_files_missing_markers(sys.argv[1:])
+
+    if missing:
+        file_lines = "\n".join(f"  - {path} [{' and '.join(problems)}]" for path, problems in missing.items())
+        print(
+            "\033[91merror:\033[0m test files are missing pytest marks "
+            "required for Buildkite CI collection.\n\n"
+            f"Level marks, e.g.: {', '.join(LEVEL_MARKERS[:4])}\n"
+            f"Hardware marks, e.g.: {', '.join(HARDWARE_MARKERS[:4])}, ...\n"
+            f"  or helpers: {', '.join(HARDWARE_HELPERS)}\n\n"
+            "The following files are missing marks:\n"
+            f"{file_lines}\n\n"
+            "To skip: SKIP=check-test-ci-coverage git commit ..."
+        )
+        sys.exit(1)