diff --git a/git_hooks/pre-commit b/git_hooks/pre-commit
index c240ebb..d3fa312 100755
--- a/git_hooks/pre-commit
+++ b/git_hooks/pre-commit
@@ -5,6 +5,6 @@
 vagrant ssh -c ". activate \
     && echo 'Checking mypy type annotations...' && mypy --no-error-summary . \
     && echo 'Checking if Black would reformat any code...' && black --check . \
-    && echo -n 'Running tests: ' && pytest -q \
+    && echo -n 'Running tests: ' && pytest -q -m 'not html_validation' \
     && echo 'Checking SCSS style...' && npm run --silent lint:scss \
     && echo 'Checking JS style...' && npm run --silent lint:js"
diff --git a/git_hooks/pre-push b/git_hooks/pre-push
index 03f7a8c..e0b2908 100755
--- a/git_hooks/pre-push
+++ b/git_hooks/pre-push
@@ -5,7 +5,7 @@
 vagrant ssh -c ". activate \
     && echo 'Checking mypy type annotations...' && mypy --no-error-summary . \
     && echo 'Checking if Black would reformat any code...' && black --check . \
-    && echo -n 'Running tests: ' && pytest -q \
+    && echo -n 'Running tests: ' && pytest -q -m '' \
     && echo 'Checking SCSS style...' && npm run --silent lint:scss \
     && echo 'Checking JS style...' && npm run --silent lint:js \
     && echo 'Checking Python style fully (takes a while)...' && prospector -M"
diff --git a/tildes/pytest.ini b/tildes/pytest.ini
index 6162a49..4e2516a 100644
--- a/tildes/pytest.ini
+++ b/tildes/pytest.ini
@@ -1,7 +1,10 @@
 [pytest]
 testpaths = tests
-addopts = -p no:cacheprovider
+addopts = -p no:cacheprovider --strict-markers -m "not (html_validation or webtest)"
 filterwarnings =
     ignore::DeprecationWarning
     ignore::PendingDeprecationWarning
     ignore::yaml.YAMLLoadWarning
+markers =
+    html_validation: mark a test as one that validates HTML using the Nu HTML Checker (very slow)
+    webtest: mark a test as one that uses the WebTest library, which goes through the actual WSGI app and involves using HTTP/HTML (more of a "functional test" than "unit test")
diff --git a/tildes/tests/conftest.py b/tildes/tests/conftest.py
index fbda3de..fe87bda 100644
--- a/tildes/tests/conftest.py
+++ b/tildes/tests/conftest.py
@@ -5,7 +5,7 @@ import os
 
 from pyramid import testing
 from pyramid.paster import get_app, get_appsettings
-from pytest import fixture
+from pytest import fixture, mark
 from redis import Redis
 from sqlalchemy import create_engine
 from sqlalchemy.engine.url import make_url
@@ -224,3 +224,12 @@ def webtest(base_app):
 def webtest_loggedout(base_app):
     """Create a logged-out webtest TestApp (function scope, so no state is retained)."""
     yield TestApp(base_app, extra_environ=WEBTEST_EXTRA_ENVIRON)
+
+
+def pytest_collection_modifyitems(items):
+    """Add "webtest" marker to any tests that use either of the WebTest fixtures."""
+    webtest_fixture_names = ("webtest", "webtest_loggedout")
+
+    for item in items:
+        if any([fixture in item.fixturenames for fixture in webtest_fixture_names]):
+            item.add_marker(mark.webtest)
diff --git a/tildes/tests/webtests/test_w3_validator.py b/tildes/tests/webtests/test_w3_validator.py
index 35ef752..35f662e 100644
--- a/tildes/tests/webtests/test_w3_validator.py
+++ b/tildes/tests/webtests/test_w3_validator.py
@@ -3,6 +3,12 @@
 
 import subprocess
 
+from pytest import mark
+
+
+# marks all tests in this module with "html_validation" marker
+pytestmark = mark.html_validation
+
 
 def test_homepage_html_loggedout(webtest_loggedout):
     """Validate HTML5 on the Tildes homepage, logged out."""