diff --git a/.github/workflows/main.yml b/.github/workflows/main.yml
index 1699261dbc..d07c4bfa29 100644
--- a/.github/workflows/main.yml
+++ b/.github/workflows/main.yml
@@ -28,6 +28,10 @@ jobs:
         run: |
           docker compose -p cms -f docker/docker-compose.test.yml run --rm testcms
 
+      - name: Run browser tests
+        run: |
+          docker compose -p cms -f docker/docker-compose.test.yml run --rm browsertestcms
+
       - name: Upload test results to Codecov
         if: ${{ !cancelled() }}
         uses: codecov/test-results-action@v1
diff --git a/Dockerfile b/Dockerfile
index 9a2827e783..8524b2af15 100644
--- a/Dockerfile
+++ b/Dockerfile
@@ -87,6 +87,13 @@ COPY --chown=cmsuser:cmsuser . /home/cmsuser/src
 
 RUN --mount=type=cache,target=/home/cmsuser/.cache/pip,uid=2000 ./install.py cms --devel
 
+# Browser tests (cmstestsuite/browser_tests)
+ENV PLAYWRIGHT_BROWSERS_PATH=/home/cmsuser/ms-playwright
+RUN --mount=type=cache,target=/home/cmsuser/.cache/pip,uid=2000 \
+    pip install -c constraints.txt ".[browser-test]" \
+    && sudo "$(which playwright)" install-deps chromium \
+    && playwright install chromium
+
 RUN <<EOF
 #!/bin/bash -ex
     sed 's|/cmsuser:your_password_here@localhost:5432/cmsdb"|/postgres@testdb:5432/cmsdbfortesting"|' \
diff --git a/cms/server/contest/static/cws_utils.js b/cms/server/contest/static/cws_utils.js
index aa86dc7161..576f0c4aa0 100644
--- a/cms/server/contest/static/cws_utils.js
+++ b/cms/server/contest/static/cws_utils.js
@@ -94,9 +94,11 @@ CMS.CWSUtils.prototype.display_notification = function(type, timestamp,
     // TODO somehow display timestamp, subject and text
 
     var alert = $('<div class="alert alert-block notification">' +
-                  '<a class="close" data-dismiss="alert" href="#">×</a>' +
+                  '<button type="button" class="close" data-dismiss="alert">×</button>' +
                   '<h4 class="alert-heading"></h4>' +
                   '</div>');
+    alert.children("button.close").attr(
+        "aria-label", $("#translation_close").text().trim());
 
     if (type == "message") {
         alert.children("h4").text($("#translation_new_message").text());
diff --git a/cms/server/contest/templates/contest.html b/cms/server/contest/templates/contest.html
index c9bf4b4870..dfa0bdee9a 100644
--- a/cms/server/contest/templates/contest.html
+++ b/cms/server/contest/templates/contest.html
@@ -81,7 +81,7 @@
     {% if handler.get_argument("login_error", "") != "" %}
         <div id="notifications" class="notifications">
             <div class="alert alert-block alert-error notification">
-                <a class="close" data-dismiss="alert" href="#">&#xD7;</a>
+                <button type="button" class="close" data-dismiss="alert" aria-label="{% trans %}Close{% endtrans %}">&#xD7;</button>
                 <h4 class="alert-heading">{% trans %}Failed to log in.{% endtrans %}</h4>
             </div>
         </div>
@@ -136,6 +136,9 @@ <h1>{% trans %}Welcome{% endtrans %}</h1>
         <div style="display: none" id="translation_new_answer">
             {% trans %}New answer{% endtrans %}
         </div>
+        <div style="display: none" id="translation_close">
+            {% trans %}Close{% endtrans %}
+        </div>
         <div style="display: none" id="translation_unread">
             {% trans %}%d unread{% endtrans %}
         </div>
diff --git a/cms/server/contest/templates/register.html b/cms/server/contest/templates/register.html
index 852cc5fcbc..7f7d7d766d 100644
--- a/cms/server/contest/templates/register.html
+++ b/cms/server/contest/templates/register.html
@@ -163,7 +163,7 @@ <h1>{% trans %}Registration{% endtrans %}</h1>
                     <div id="username-input" class="control-group">
                         <label class="control-label" for="username">{% trans %}Username{% endtrans %}</label>
                         <div class="controls">
-                            <input required minlength="1" maxlength="{{ MAX_INPUT_LENGTH }}" pattern="^[A-Za-z0-9_-]+$" type="text" class="input-xlarge" name="username" id="username">
+                            <input required minlength="1" maxlength="{{ MAX_INPUT_LENGTH }}" pattern="^[A-Za-z0-9_\-]+$" type="text" class="input-xlarge" name="username" id="username">
                             <span class="help-block"></span>
                         </div>
                     </div>
diff --git a/cms/server/contest/templates/task_submissions.html b/cms/server/contest/templates/task_submissions.html
index 6ffc3d1ba3..2959febc5e 100644
--- a/cms/server/contest/templates/task_submissions.html
+++ b/cms/server/contest/templates/task_submissions.html
@@ -400,7 +400,7 @@ <h3>{% trans %}Official submissions{% endtrans %}</h3>
 
 <div class="modal fade hide wide" id="submission_detail">
     <div class="modal-header">
-        <button type="button" class="close" data-dismiss="modal">&#xD7;</button>
+        <button type="button" class="close" data-dismiss="modal" aria-label="{% trans %}Close{% endtrans %}">&#xD7;</button>
         <h3>{% trans %}Submission details{% endtrans %}</h3>
     </div>
     <div class="modal-body">
diff --git a/cms/server/contest/templates/test_interface.html b/cms/server/contest/templates/test_interface.html
index 104e3a74ad..226550e64c 100644
--- a/cms/server/contest/templates/test_interface.html
+++ b/cms/server/contest/templates/test_interface.html
@@ -236,7 +236,7 @@ <h2 style="margin: 40px 0 10px">{% trans %}Previous tests{% endtrans %}</h2>
 
 <div class="modal fade hide" id="user_test_detail">
     <div class="modal-header">
-        <button type="button" class="close" data-dismiss="modal">&#xD7;</button>
+        <button type="button" class="close" data-dismiss="modal" aria-label="{% trans %}Close{% endtrans %}">&#xD7;</button>
         <h3>{% trans %}Test details{% endtrans %}</h3>
     </div>
     <div class="modal-body">
diff --git a/cmstestsuite/browser_tests/__init__.py b/cmstestsuite/browser_tests/__init__.py
new file mode 100644
index 0000000000..aa835ee662
--- /dev/null
+++ b/cmstestsuite/browser_tests/__init__.py
@@ -0,0 +1,16 @@
+#!/usr/bin/env python3
+
+# Contest Management System - http://cms-dev.github.io/
+#
+# This program is free software: you can redistribute it and/or modify
+# it under the terms of the GNU Affero General Public License as
+# published by the Free Software Foundation, either version 3 of the
+# License, or (at your option) any later version.
+#
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU Affero General Public License for more details.
+#
+# You should have received a copy of the GNU Affero General Public License
+# along with this program.  If not, see <http://www.gnu.org/licenses/>.
diff --git a/cmstestsuite/browser_tests/communication_test.py b/cmstestsuite/browser_tests/communication_test.py
new file mode 100644
index 0000000000..ac6dddcfc5
--- /dev/null
+++ b/cmstestsuite/browser_tests/communication_test.py
@@ -0,0 +1,52 @@
+#!/usr/bin/env python3
+
+# Contest Management System - http://cms-dev.github.io/
+# Copyright © 2026 Pasit Sangprachathanarak <ouipingpasit@gmail.com>
+#
+# This program is free software: you can redistribute it and/or modify
+# it under the terms of the GNU Affero General Public License as
+# published by the Free Software Foundation, either version 3 of the
+# License, or (at your option) any later version.
+#
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU Affero General Public License for more details.
+#
+# You should have received a copy of the GNU Affero General Public License
+# along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
+"""Browser tests for the communication page."""
+
+from playwright.sync_api import expect
+
+from cmstestsuite.browser_tests import seed
+
+
+def test_shows_announcements_messages_and_answers(page, base_url, login):
+    login(seed.READER)
+    page.get_by_role("link", name="Communication").click()
+    expect(page.get_by_text(seed.ANNOUNCEMENT_SUBJECT)).to_be_visible()
+    expect(page.get_by_text(seed.MESSAGE_SUBJECT)).to_be_visible()
+    expect(page.get_by_text(seed.ANSWERED_QUESTION_SUBJECT).first) \
+        .to_be_visible()
+    expect(page.get_by_text(seed.ANSWER_TEXT)).to_be_visible()
+
+
+def test_ask_a_question(page, base_url, login):
+    login(seed.ASKER)
+    page.get_by_role("link", name="Communication").click()
+    page.locator("#input_subject").fill("Where is the toilet?")
+    page.locator("#input_text").fill("Asking for a friend.")
+    page.get_by_role("button", name="Ask question").click()
+
+    page.get_by_role("link", name="Communication").click()
+    expect(page.get_by_text("Where is the toilet?").first).to_be_visible()
+
+
+def test_reset_clears_the_question_form(page, base_url, login):
+    login(seed.ASKER)
+    page.get_by_role("link", name="Communication").click()
+    page.locator("#input_subject").fill("draft")
+    page.get_by_role("button", name="Reset").click()
+    expect(page.locator("#input_subject")).to_have_value("")
diff --git a/cmstestsuite/browser_tests/conftest.py b/cmstestsuite/browser_tests/conftest.py
new file mode 100644
index 0000000000..c91ab4d868
--- /dev/null
+++ b/cmstestsuite/browser_tests/conftest.py
@@ -0,0 +1,161 @@
+#!/usr/bin/env python3
+
+# Contest Management System - http://cms-dev.github.io/
+# Copyright © 2026 Pasit Sangprachathanarak <ouipingpasit@gmail.com>
+#
+# This program is free software: you can redistribute it and/or modify
+# it under the terms of the GNU Affero General Public License as
+# published by the Free Software Foundation, either version 3 of the
+# License, or (at your option) any later version.
+#
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU Affero General Public License for more details.
+#
+# You should have received a copy of the GNU Affero General Public License
+# along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
+"""Fixtures for the browser tests of the contest web server (CWS).
+
+The tests need the "browser-test" extra (Playwright and its browsers),
+a PostgreSQL database whose name ends in "fortesting", and a CMS_CONFIG
+pointing to it. They are run with:
+
+    pytest cmstestsuite/browser_tests
+
+"""
+
+import os
+import subprocess
+import sys
+import time
+import urllib.error
+import urllib.request
+
+import pytest
+
+pytest.importorskip(
+    "playwright", reason="install the 'browser-test' extra to run these tests")
+
+from cms import config as cms_config  # noqa: E402
+from cmstestsuite.browser_tests import seed  # noqa: E402
+
+
+def pytest_collection_modifyitems(items):
+    here = os.path.dirname(__file__)
+    for item in items:
+        if str(item.fspath).startswith(here):
+            item.add_marker(pytest.mark.browser)
+
+
+def pytest_configure(config):
+    config.addinivalue_line(
+        "markers", "browser: drives a real browser against a running CWS")
+    config.addinivalue_line(
+        "markers",
+        "allow_browser_errors: do not fail on console errors, page errors "
+        "or failed static assets")
+
+
+@pytest.fixture(scope="session")
+def seeded():
+    """Recreate the test database and fill it with the fixtures."""
+    return seed.seed_database()
+
+
+@pytest.fixture(scope="session")
+def base_url(seeded):
+    """Start a real CWS on the seeded contest, and return its URL.
+
+    Only the CWS runs: the seeded submissions are already evaluated, so
+    no worker or evaluation service is needed.
+
+    """
+    port = cms_config.contest_web_server.listen_port[0]
+    url = "http://127.0.0.1:%d/" % port
+    executable = os.path.join(sys.prefix, "bin", "cmsContestWebServer")
+    verbose = os.environ.get("CMS_BROWSER_TEST_VERBOSE")
+    proc = subprocess.Popen(
+        [executable, "0", "-c", str(seeded.contest_id)],
+        stdout=None if verbose else subprocess.DEVNULL,
+        stderr=None if verbose else subprocess.STDOUT)
+    try:
+        deadline = time.monotonic() + 60
+        while True:
+            if proc.poll() is not None:
+                raise RuntimeError(
+                    "ContestWebServer exited early with code %s "
+                    "(set CMS_BROWSER_TEST_VERBOSE=1 to see its output)"
+                    % proc.returncode)
+            try:
+                urllib.request.urlopen(url, timeout=2).close()
+                break
+            except (urllib.error.URLError, OSError):
+                if time.monotonic() > deadline:
+                    raise RuntimeError("ContestWebServer did not come up")
+                time.sleep(0.3)
+        yield url
+    finally:
+        proc.terminate()
+        try:
+            proc.wait(timeout=10)
+        except subprocess.TimeoutExpired:
+            proc.kill()
+
+
+@pytest.fixture(scope="session")
+def browser_context_args(browser_context_args):
+    return {
+        **browser_context_args,
+        "viewport": {"width": 1280, "height": 900},
+        "locale": "en-US",
+    }
+
+
+# Console messages that are known to be noise rather than regressions.
+# Keep this list short and explain each entry.
+ALLOWED_CONSOLE_ERRORS: list[str] = []
+
+
+@pytest.fixture(autouse=True)
+def fail_on_browser_errors(request, page):
+    """Fail a test on console errors, page errors or broken static files.
+
+    This catches broken JavaScript and missing CSS/JS assets, which are
+    the typical symptom of a front-end framework migration gone wrong.
+
+    """
+    problems: list[str] = []
+
+    def on_console(msg):
+        if msg.type == "error" and not any(
+                a in msg.text for a in ALLOWED_CONSOLE_ERRORS):
+            problems.append("console error: %s" % msg.text)
+
+    def on_page_error(exc):
+        problems.append("uncaught exception: %s" % exc)
+
+    def on_response(response):
+        if "/static/" in response.url and response.status >= 400:
+            problems.append(
+                "static asset %s returned %d" % (response.url, response.status))
+
+    page.on("console", on_console)
+    page.on("pageerror", on_page_error)
+    page.on("response", on_response)
+    yield
+    if request.node.get_closest_marker("allow_browser_errors") is None:
+        assert not problems, "\n".join(problems)
+
+
+@pytest.fixture
+def login(page, base_url, seeded):
+    """Return a function logging a seeded user in to the contest."""
+    def do_login(username: str):
+        page.goto(base_url)
+        page.get_by_label("Username").fill(username)
+        page.get_by_label("Password").fill(seed.PASSWORDS[username])
+        page.get_by_role("button", name="Login").click()
+        page.get_by_role("button", name="Logout").wait_for()
+    return do_login
diff --git a/cmstestsuite/browser_tests/downloads_test.py b/cmstestsuite/browser_tests/downloads_test.py
new file mode 100644
index 0000000000..75b5ef583c
--- /dev/null
+++ b/cmstestsuite/browser_tests/downloads_test.py
@@ -0,0 +1,65 @@
+#!/usr/bin/env python3
+
+# Contest Management System - http://cms-dev.github.io/
+# Copyright © 2026 Pasit Sangprachathanarak <ouipingpasit@gmail.com>
+#
+# This program is free software: you can redistribute it and/or modify
+# it under the terms of the GNU Affero General Public License as
+# published by the Free Software Foundation, either version 3 of the
+# License, or (at your option) any later version.
+#
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU Affero General Public License for more details.
+#
+# You should have received a copy of the GNU Affero General Public License
+# along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
+"""Browser tests for the dropdown menu to download a submission made of
+several files, and for the table in the details dialog."""
+
+from playwright.sync_api import expect
+
+from cmstestsuite.browser_tests import seed
+
+
+def open_pair_submissions(page, base_url):
+    page.goto("%stasks/%s/submissions" % (base_url, seed.PAIR_TASK_NAME))
+
+
+def test_multi_file_download_menu_opens_and_closes(page, base_url, login):
+    login(seed.READER)
+    open_pair_submissions(page, base_url)
+    first, second = seed.PAIR_FILES
+    item = page.get_by_role("link", name=first)
+    expect(item).to_be_hidden()
+
+    page.get_by_text("Download", exact=True).first.click()
+    expect(item).to_be_visible()
+    expect(page.get_by_role("link", name=second)).to_be_visible()
+
+    # Clicking elsewhere closes the menu.
+    page.get_by_role("heading").first.click()
+    expect(item).to_be_hidden()
+
+
+def test_multi_file_download_menu_downloads_a_file(page, base_url, login):
+    login(seed.READER)
+    open_pair_submissions(page, base_url)
+    page.get_by_text("Download", exact=True).first.click()
+    with page.expect_download() as info:
+        page.get_by_role("link", name=seed.PAIR_FILES[1]).click()
+    assert info.value.suggested_filename == seed.PAIR_FILES[1]
+
+
+def test_details_dialog_lists_testcases_in_a_table(page, base_url, login):
+    login(seed.READER)
+    page.goto("%stasks/%s/submissions" % (base_url, seed.TASK_NAME))  # noqa: UP031
+    page.get_by_text("details", exact=True).first.click()
+    dialog = page.locator("#submission_detail")
+    table = dialog.get_by_role("table").filter(has_text="Correct")
+    expect(table).to_be_visible()
+    expect(dialog.get_by_role("columnheader", name="Outcome")).to_be_visible()
+    expect(dialog.get_by_role("cell", name="Correct", exact=True)) \
+        .to_be_visible()
diff --git a/cmstestsuite/browser_tests/login_test.py b/cmstestsuite/browser_tests/login_test.py
new file mode 100644
index 0000000000..0549678e5a
--- /dev/null
+++ b/cmstestsuite/browser_tests/login_test.py
@@ -0,0 +1,71 @@
+#!/usr/bin/env python3
+
+# Contest Management System - http://cms-dev.github.io/
+# Copyright © 2026 Pasit Sangprachathanarak <ouipingpasit@gmail.com>
+#
+# This program is free software: you can redistribute it and/or modify
+# it under the terms of the GNU Affero General Public License as
+# published by the Free Software Foundation, either version 3 of the
+# License, or (at your option) any later version.
+#
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU Affero General Public License for more details.
+#
+# You should have received a copy of the GNU Affero General Public License
+# along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
+"""Browser tests for logging in and out of CWS."""
+
+import re
+
+from playwright.sync_api import expect
+
+from cmstestsuite.browser_tests import seed
+
+
+def test_login_page_shows_form(page, base_url):
+    page.goto(base_url)
+    expect(page.get_by_label("Username")).to_be_visible()
+    expect(page.get_by_label("Password")).to_be_visible()
+    expect(page.get_by_role("button", name="Login")).to_be_visible()
+    expect(page.get_by_text("Failed to log in.")).to_have_count(0)
+
+
+def test_login_and_logout(page, base_url, login):
+    login(seed.READER)
+    expect(page.get_by_text("Logged in as")).to_contain_text("Alice Tester")
+    expect(page.get_by_role("heading", name="Overview", exact=True)).to_be_visible()
+
+    page.get_by_role("button", name="Logout").click()
+    expect(page.get_by_role("button", name="Login")).to_be_visible()
+    expect(page.get_by_role("button", name="Logout")).to_have_count(0)
+
+
+def test_failed_login_alert_can_be_dismissed(page, base_url):
+    page.goto(base_url)
+    page.get_by_label("Username").fill(seed.READER)
+    page.get_by_label("Password").fill("not-the-password")
+    page.get_by_role("button", name="Login").click()
+
+    alert = page.get_by_text("Failed to log in.")
+    expect(alert).to_be_visible()
+    expect(page.get_by_role("button", name="Logout")).to_have_count(0)
+
+    # The alert has a close control; using it must remove the alert.
+    page.get_by_role("button", name="Close").click()
+    expect(alert).to_be_hidden()
+
+
+def test_reset_button_clears_the_login_form(page, base_url):
+    page.goto(base_url)
+    page.get_by_label("Username").fill("something")
+    page.get_by_role("button", name="Reset").click()
+    expect(page.get_by_label("Username")).to_have_value("")
+
+
+def test_registration_link_opens_registration_page(page, base_url):
+    page.goto(base_url)
+    page.get_by_role("link", name="Register").click()
+    expect(page).to_have_url(re.compile(r"/register$"))
diff --git a/cmstestsuite/browser_tests/navigation_test.py b/cmstestsuite/browser_tests/navigation_test.py
new file mode 100644
index 0000000000..9b62b4f239
--- /dev/null
+++ b/cmstestsuite/browser_tests/navigation_test.py
@@ -0,0 +1,87 @@
+#!/usr/bin/env python3
+
+# Contest Management System - http://cms-dev.github.io/
+# Copyright © 2026 Pasit Sangprachathanarak <ouipingpasit@gmail.com>
+#
+# This program is free software: you can redistribute it and/or modify
+# it under the terms of the GNU Affero General Public License as
+# published by the Free Software Foundation, either version 3 of the
+# License, or (at your option) any later version.
+#
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU Affero General Public License for more details.
+#
+# You should have received a copy of the GNU Affero General Public License
+# along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
+"""Browser tests for the pages reachable from the navigation menu."""
+
+import re
+
+import pytest
+from playwright.sync_api import expect
+
+from cmstestsuite.browser_tests import seed
+
+
+@pytest.fixture
+def reader(page, login):
+    login(seed.READER)
+    return page
+
+
+def test_overview(reader):
+    expect(reader.get_by_role("heading", name="Overview", exact=True)).to_be_visible()
+    expect(reader.get_by_text("The contest is currently running.")) \
+        .to_be_visible()
+    expect(reader.get_by_text("Server time:")).to_be_visible()
+
+
+def test_navigation_menu_lists_task_and_pages(reader):
+    for name in ("Overview", "Communication", "Statement", "Submissions",
+                 "Documentation"):
+        expect(reader.get_by_role("link", name=name).first).to_be_visible()
+
+
+def test_server_clock_ticks(reader):
+    clock = reader.locator("#server_time")
+    first = clock.inner_text()
+    expect(clock).not_to_have_text(first, timeout=5000)
+
+
+def test_task_statement(reader):
+    reader.get_by_role("link", name="Statement").first.click()
+    expect(reader).to_have_url(
+        re.compile(r"/tasks/%s/description$" % seed.TASK_NAME))
+    expect(reader.get_by_text(seed.TASK_TITLE).first).to_be_visible()
+    expect(reader.locator("a[href*='/statements/']").first).to_be_visible()
+
+
+def test_documentation(reader):
+    reader.get_by_role("link", name="Documentation").click()
+    expect(reader).to_have_url(re.compile(r"/documentation$"))
+    expect(reader.get_by_role("heading").first).to_be_visible()
+
+
+def test_language_selector_switches_language(reader):
+    selector = reader.locator("#lang")
+    if selector.count() == 0:
+        pytest.skip("only one translation is installed")
+    codes = [o.get_attribute("value")
+             for o in selector.locator("option").all()]
+    target = next(c for c in codes if c and not c.startswith("en"))
+    with reader.expect_navigation():
+        selector.select_option(target)
+    expect(reader.locator("#lang")).to_have_value(target)
+    # Put the automatic language back, so later tests see English.
+    with reader.expect_navigation():
+        reader.locator("#lang").select_option("")
+
+
+@pytest.mark.allow_browser_errors
+def test_unknown_task_shows_error_page(reader, base_url):
+    response = reader.goto(base_url + "tasks/does-not-exist/description")
+    assert response.status == 404
+    expect(reader.get_by_text("404").first).to_be_visible()
diff --git a/cmstestsuite/browser_tests/notifications_test.py b/cmstestsuite/browser_tests/notifications_test.py
new file mode 100644
index 0000000000..d196c94636
--- /dev/null
+++ b/cmstestsuite/browser_tests/notifications_test.py
@@ -0,0 +1,40 @@
+#!/usr/bin/env python3
+
+# Contest Management System - http://cms-dev.github.io/
+# Copyright © 2026 Pasit Sangprachathanarak <ouipingpasit@gmail.com>
+#
+# This program is free software: you can redistribute it and/or modify
+# it under the terms of the GNU Affero General Public License as
+# published by the Free Software Foundation, either version 3 of the
+# License, or (at your option) any later version.
+#
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU Affero General Public License for more details.
+#
+# You should have received a copy of the GNU Affero General Public License
+# along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
+"""Browser tests for the alerts that CWS builds in JavaScript when there
+is something new (announcement, message, answer)."""
+
+from playwright.sync_api import expect
+
+from cmstestsuite.browser_tests import seed
+
+
+def test_notifications_are_shown_and_can_be_dismissed(page, base_url, login):
+    login(seed.READER)
+    # An announcement, a message and an answer exist before the login.
+    notifications = page.locator("#notifications > *")
+    expect(notifications).to_have_count(3)
+    expect(page.locator("#unread_count")).to_contain_text("3")
+
+    notifications.first.get_by_role("button", name="Close").click()
+    expect(notifications).to_have_count(2)
+
+
+def test_user_without_news_sees_only_the_announcement(page, base_url, login):
+    login(seed.NOBODY)
+    expect(page.locator("#notifications > *")).to_have_count(1)
diff --git a/cmstestsuite/browser_tests/registration_test.py b/cmstestsuite/browser_tests/registration_test.py
new file mode 100644
index 0000000000..1ca0a9aeb4
--- /dev/null
+++ b/cmstestsuite/browser_tests/registration_test.py
@@ -0,0 +1,104 @@
+#!/usr/bin/env python3
+
+# Contest Management System - http://cms-dev.github.io/
+# Copyright © 2026 Pasit Sangprachathanarak <ouipingpasit@gmail.com>
+#
+# This program is free software: you can redistribute it and/or modify
+# it under the terms of the GNU Affero General Public License as
+# published by the Free Software Foundation, either version 3 of the
+# License, or (at your option) any later version.
+#
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU Affero General Public License for more details.
+#
+# You should have received a copy of the GNU Affero General Public License
+# along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
+"""Browser tests for the registration form: both tabs, the validation
+messages and the confirmation."""
+
+import pytest
+from playwright.sync_api import expect
+
+from cmstestsuite.browser_tests import seed
+
+
+def fill_new_user(page, username, password, confirm=None):
+    page.locator("#first_name").fill("New")
+    page.locator("#last_name").fill("Person")
+    page.locator("#username").fill(username)
+    page.locator("#password").fill(password)
+    page.locator("#password-confirm").fill(
+        password if confirm is None else confirm)
+
+
+def test_tabs_switch_between_new_user_and_join(page, base_url):
+    page.goto(base_url + "register")
+    # The new user tab is shown first, with the whole form.
+    expect(page.locator("#profile")).to_be_visible()
+    expect(page.locator("#first_name")).to_be_visible()
+    expect(page.locator("#password-confirm")).to_be_visible()
+
+    # Joining with an existing user hides the profile and the password
+    # confirmation.
+    page.locator("#join-pill").get_by_role("link").click()
+    expect(page.locator("#profile")).to_be_hidden()
+    expect(page.locator("#first_name")).to_be_hidden()
+    expect(page.locator("#password-confirm")).to_be_hidden()
+    expect(page.locator("#username")).to_be_visible()
+    expect(page.locator("#password")).to_be_visible()
+
+    page.locator("#register-pill").get_by_role("link").click()
+    expect(page.locator("#profile")).to_be_visible()
+    expect(page.locator("#first_name")).to_be_visible()
+    expect(page.locator("#password-confirm")).to_be_visible()
+
+
+def test_mismatching_passwords_show_an_error(page, base_url):
+    page.goto(base_url + "register")
+    fill_new_user(page, "mismatch-user", "a-long-password", "another-one-12")
+    page.get_by_role("button", name="Register").click()
+    expect(page.get_by_text("The passwords do not match!")).to_be_visible()
+    expect(page.locator("#confirmed-mask")).to_be_hidden()
+
+
+def test_register_a_new_user(page, base_url):
+    page.goto(base_url + "register")
+    fill_new_user(page, "fresh-user", "a-long-password")
+    page.get_by_role("button", name="Register").click()
+    expect(page.locator("#confirmed-mask")).to_be_visible()
+    expect(page.locator("#show-username")).to_have_text("fresh-user")
+    expect(page.locator("#signup-mask")).to_be_hidden()
+
+
+# The next three tests make the server answer 409 or 404 on purpose, and
+# Chromium logs failed requests as console errors.
+@pytest.mark.allow_browser_errors
+def test_taken_username_shows_an_error(page, base_url):
+    page.goto(base_url + "register")
+    fill_new_user(page, seed.READER, "a-long-password")
+    page.get_by_role("button", name="Register").click()
+    expect(page.get_by_text("This username is already taken")).to_be_visible()
+    expect(page.locator("#confirmed-mask")).to_be_hidden()
+
+
+@pytest.mark.allow_browser_errors
+def test_joining_when_already_registered_shows_an_error(page, base_url):
+    page.goto(base_url + "register")
+    page.locator("#join-pill").get_by_role("link").click()
+    page.locator("#username").fill(seed.READER)
+    page.locator("#password").fill(seed.PASSWORDS[seed.READER])
+    page.get_by_role("button", name="Register").click()
+    expect(page.get_by_text("This user is already registered")).to_be_visible()
+
+
+@pytest.mark.allow_browser_errors
+def test_joining_with_an_unknown_user_shows_an_error(page, base_url):
+    page.goto(base_url + "register")
+    page.locator("#join-pill").get_by_role("link").click()
+    page.locator("#username").fill("nobody-by-that-name")
+    page.locator("#password").fill("whatever-password")
+    page.get_by_role("button", name="Register").click()
+    expect(page.get_by_text("No such user.")).to_be_visible()
diff --git a/cmstestsuite/browser_tests/seed.py b/cmstestsuite/browser_tests/seed.py
new file mode 100644
index 0000000000..8f44a89ed7
--- /dev/null
+++ b/cmstestsuite/browser_tests/seed.py
@@ -0,0 +1,334 @@
+#!/usr/bin/env python3
+
+# Contest Management System - http://cms-dev.github.io/
+# Copyright © 2026 Pasit Sangprachathanarak <ouipingpasit@gmail.com>
+#
+# This program is free software: you can redistribute it and/or modify
+# it under the terms of the GNU Affero General Public License as
+# published by the Free Software Foundation, either version 3 of the
+# License, or (at your option) any later version.
+#
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU Affero General Public License for more details.
+#
+# You should have received a copy of the GNU Affero General Public License
+# along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
+"""Seed the test database with the objects the browser tests rely on.
+
+The data is created through the helpers of DatabaseObjectGeneratorMixin,
+so the browser tests do not depend on the import path of cmscontrib.
+
+"""
+
+import hashlib
+from dataclasses import dataclass
+from datetime import datetime, timedelta, timezone
+
+from cms.db import Announcement, File, Message, Question, Session, \
+    Statement, SubmissionResult, Testcase, UserTest, UserTestFile, \
+    UserTestResult, drop_db, engine, init_db
+from cms.db.filecacher import DBBackend
+from cmscommon.crypto import build_password
+from cmstestsuite.unit_tests.databasemixin import DatabaseObjectGeneratorMixin
+
+
+# Names of the languages enabled in the seeded contest.
+LANGUAGES = ["C++20 / g++", "Python 3 / CPython"]
+
+CONTEST_DESCRIPTION = "Browser Test Contest"
+TASK_NAME = "sum"
+TASK_TITLE = "Sum of two numbers"
+# A second task whose submissions consist of two files, which makes CWS
+# show a menu to download them instead of a single link.
+PAIR_TASK_NAME = "pair"
+PAIR_FILES = ["pair_a.py", "pair_b.py"]
+ANNOUNCEMENT_SUBJECT = "Welcome to the contest"
+MESSAGE_SUBJECT = "A private message"
+ANSWERED_QUESTION_SUBJECT = "Is the input sorted?"
+ANSWER_TEXT = "Yes, it is sorted."
+
+# Users that never change state: tests using them may run in any order.
+READER = "alice"
+# Users reserved for flows that change state.
+SUBMITTER = "bob"
+TOKEN_USER = "carol"
+ASKER = "dave"
+# A user without any submission, to check the empty state.
+NOBODY = "erin"
+
+PASSWORDS = {
+    name: name + "-password"
+    for name in (READER, SUBMITTER, TOKEN_USER, ASKER, NOBODY)
+}
+
+
+@dataclass
+class SeededData:
+    contest_id: int
+    contest_name: str
+    task_name: str
+    # Number of finished submissions of READER on the task.
+    reader_submissions: int
+    # Number of finished, not yet tokened submissions of TOKEN_USER.
+    token_user_submissions: int
+
+
+def _now() -> datetime:
+    return datetime.now(timezone.utc).replace(tzinfo=None)
+
+
+def _store_file(content: bytes) -> str:
+    """Put content in the file store, and return its digest."""
+    digest = hashlib.sha1(content).hexdigest()
+    backend = DBBackend()
+    fobj = backend.create_file(digest)
+    if fobj is None:
+        # The same content was already stored.
+        return digest
+    fobj.write(content)
+    backend.commit_file(fobj, digest)
+    return digest
+
+
+def seed_database() -> SeededData:
+    """Recreate the database and fill it with the test fixtures.
+
+    Refuses to run on a database whose name does not end in "fortesting".
+
+    """
+    assert engine.url.database.endswith("fortesting"), (
+        "The database name is not in the form '<name>fortesting' and "
+        "this could mean that you're running tests on the wrong database. "
+        "Aborting")
+    drop_db()
+    init_db()
+
+    gen = DatabaseObjectGeneratorMixin
+    session = Session()
+
+    contest = gen.get_contest(
+        name="browsertest",
+        description=CONTEST_DESCRIPTION,
+        languages=LANGUAGES,
+        allow_questions=True,
+        allow_registration=True,
+        allow_user_tests=True,
+        token_mode="infinite",
+    )
+    session.add(contest)
+
+    task = gen.get_task(
+        name=TASK_NAME,
+        title=TASK_TITLE,
+        contest=contest,
+        num=0,
+        submission_format=["sum.%l"],
+        token_mode="infinite",
+    )
+    dataset = gen.get_dataset(
+        task=task,
+        description="Browser test dataset",
+        autojudge=False,
+        time_limit=1.0,
+        memory_limit=256 * 1024 * 1024,
+        task_type="Batch",
+        task_type_parameters=["alone", ["", ""], "diff"],
+        score_type="Sum",
+        score_type_parameters=50,
+    )
+    task.active_dataset = dataset
+    session.add(task)
+    session.add(dataset)
+
+    pdf = b"%PDF-1.4\n1 0 obj<</Type/Catalog>>endobj\ntrailer<</Root 1 0 R>>\n"
+    session.add(Statement(task=task, digest=_store_file(pdf), language="en"))
+
+    # A single public testcase gives the task a maximum score, which makes
+    # CWS show the score column.
+    session.add(Testcase(
+        dataset=dataset, codename="1", public=True,
+        input=_store_file(b"1 2\n"), output=_store_file(b"3\n")))
+
+    pair_task = gen.get_task(
+        name=PAIR_TASK_NAME,
+        title="Two files",
+        contest=contest,
+        num=1,
+        submission_format=["pair_a.%l", "pair_b.%l"],
+        token_mode="infinite",
+    )
+    pair_dataset = gen.get_dataset(
+        task=pair_task,
+        description="Browser test dataset",
+        autojudge=False,
+        time_limit=1.0,
+        memory_limit=256 * 1024 * 1024,
+        task_type="Batch",
+        task_type_parameters=["alone", ["", ""], "diff"],
+        score_type="Sum",
+        score_type_parameters=50,
+    )
+    pair_task.active_dataset = pair_dataset
+    session.add(pair_task)
+    session.add(pair_dataset)
+    session.add(Statement(
+        task=pair_task, digest=_store_file(pdf), language="en"))
+    session.add(Testcase(
+        dataset=pair_dataset, codename="1", public=True,
+        input=_store_file(b"1 2\n"), output=_store_file(b"3\n")))
+
+    users = {}
+    participations = {}
+    for name, password in PASSWORDS.items():
+        user = gen.get_user(
+            username=name,
+            first_name=name.capitalize(),
+            last_name="Tester",
+            password=build_password(password),
+        )
+        users[name] = user
+        participations[name] = gen.get_participation(
+            user=user, contest=contest)
+        session.add(participations[name])
+
+    session.add(Announcement(
+        contest=contest,
+        subject=ANNOUNCEMENT_SUBJECT,
+        text="Good luck to everyone.",
+        timestamp=_now() - timedelta(hours=1)))
+    session.add(Message(
+        participation=participations[READER],
+        subject=MESSAGE_SUBJECT,
+        text="Please remember to read the rules.",
+        timestamp=_now() - timedelta(hours=1)))
+    session.add(Question(
+        participation=participations[READER],
+        subject=ANSWERED_QUESTION_SUBJECT,
+        text="Can I assume the input is sorted?",
+        question_timestamp=_now() - timedelta(hours=2),
+        reply_timestamp=_now() - timedelta(hours=1),
+        reply_subject="Re: " + ANSWERED_QUESTION_SUBJECT,
+        reply_text=ANSWER_TEXT,
+        ignored=False))
+
+    source = _store_file(b"print(sum(map(int, input().split())))\n")
+
+    def add_finished_submission(name: str, index: int):
+        submission = gen.get_submission(
+            task=task,
+            participation=participations[name],
+            language="Python 3 / CPython",
+            timestamp=_now() - timedelta(minutes=30 - index),
+            opaque_id=1000 * (1 + list(PASSWORDS).index(name)) + index,
+        )
+        session.add(submission)
+        session.add(File(
+            submission=submission, filename="sum.%l", digest=source))
+        details = [{
+            "idx": 1,
+            "outcome": "Correct",
+            "text": ["Output is correct"],
+            "time": 0.01,
+            "memory": 1024 * 1024,
+        }]
+        session.add(SubmissionResult(
+            submission=submission,
+            dataset=dataset,
+            compilation_outcome="ok",
+            compilation_text=["OK"],
+            compilation_tries=1,
+            evaluation_outcome="ok",
+            evaluation_tries=1,
+            score=50.0,
+            score_details=details,
+            public_score=50.0,
+            public_score_details=details,
+            ranking_score_details=["50"],
+        ))
+        return submission
+
+    reader_submissions = 2
+    for i in range(reader_submissions):
+        add_finished_submission(READER, i)
+    token_user_submissions = 2
+    for i in range(token_user_submissions):
+        add_finished_submission(TOKEN_USER, i)
+
+    # A finished submission made of two files, to get the download menu.
+    pair_submission = gen.get_submission(
+        task=pair_task,
+        participation=participations[READER],
+        language="Python 3 / CPython",
+        timestamp=_now() - timedelta(minutes=20),
+        opaque_id=9000,
+    )
+    session.add(pair_submission)
+    for name in ("pair_a.%l", "pair_b.%l"):
+        session.add(File(
+            submission=pair_submission, filename=name, digest=source))
+    pair_details = [{
+        "idx": 1,
+        "outcome": "Correct",
+        "text": ["Output is correct"],
+        "time": 0.01,
+        "memory": 1024 * 1024,
+    }]
+    session.add(SubmissionResult(
+        submission=pair_submission,
+        dataset=pair_dataset,
+        compilation_outcome="ok",
+        compilation_text=["OK"],
+        compilation_tries=1,
+        evaluation_outcome="ok",
+        evaluation_tries=1,
+        score=50.0,
+        score_details=pair_details,
+        public_score=50.0,
+        public_score_details=pair_details,
+        ranking_score_details=["50"],
+    ))
+
+    # Finished user tests: one with a single file, one with two files.
+    test_input = _store_file(b"1 2\n")
+    test_output = _store_file(b"3\n")
+    for task_, dataset_, names in (
+            (task, dataset, ["sum.%l"]),
+            (pair_task, pair_dataset, ["pair_a.%l", "pair_b.%l"])):
+        user_test = UserTest(
+            participation=participations[READER],
+            task=task_,
+            timestamp=_now() - timedelta(minutes=10),
+            language="Python 3 / CPython",
+            input=test_input,
+        )
+        session.add(user_test)
+        for name in names:
+            session.add(UserTestFile(
+                user_test=user_test, filename=name, digest=source))
+        session.add(UserTestResult(
+            user_test=user_test,
+            dataset=dataset_,
+            output=test_output,
+            compilation_outcome="ok",
+            compilation_text=["OK"],
+            compilation_tries=1,
+            evaluation_outcome="ok",
+            evaluation_text=["Execution completed successfully"],
+            evaluation_tries=1,
+            execution_time=0.01,
+            execution_memory=1024 * 1024,
+        ))
+
+    session.commit()
+    result = SeededData(
+        contest_id=contest.id,
+        contest_name=contest.name,
+        task_name=TASK_NAME,
+        reader_submissions=reader_submissions,
+        token_user_submissions=token_user_submissions,
+    )
+    session.close()
+    return result
diff --git a/cmstestsuite/browser_tests/smoke_test.py b/cmstestsuite/browser_tests/smoke_test.py
new file mode 100644
index 0000000000..66694dfd58
--- /dev/null
+++ b/cmstestsuite/browser_tests/smoke_test.py
@@ -0,0 +1,47 @@
+#!/usr/bin/env python3
+
+# Contest Management System - http://cms-dev.github.io/
+# Copyright © 2026 Pasit Sangprachathanarak <ouipingpasit@gmail.com>
+#
+# This program is free software: you can redistribute it and/or modify
+# it under the terms of the GNU Affero General Public License as
+# published by the Free Software Foundation, either version 3 of the
+# License, or (at your option) any later version.
+#
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU Affero General Public License for more details.
+#
+# You should have received a copy of the GNU Affero General Public License
+# along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
+"""Smoke tests: every page loads for a logged-in user. Console errors and
+missing static files are reported by the autouse fixture in conftest.py."""
+
+import pytest
+
+from cmstestsuite.browser_tests import seed
+
+
+@pytest.mark.parametrize("path", [
+    "",
+    "communication",
+    "documentation",
+    "tasks/%s/description" % seed.TASK_NAME,
+    "tasks/%s/submissions" % seed.TASK_NAME,
+    "tasks/%s/description" % seed.PAIR_TASK_NAME,
+    "tasks/%s/submissions" % seed.PAIR_TASK_NAME,
+    "testing",
+])
+def test_page_loads(page, base_url, login, path):
+    login(seed.READER)
+    response = page.goto(base_url + path)
+    assert response.status == 200
+    page.wait_for_load_state("networkidle")
+
+
+def test_registration_page_loads(page, base_url):
+    response = page.goto(base_url + "register")
+    assert response.status == 200
+    page.wait_for_load_state("networkidle")
diff --git a/cmstestsuite/browser_tests/submissions_test.py b/cmstestsuite/browser_tests/submissions_test.py
new file mode 100644
index 0000000000..8d4ebe4444
--- /dev/null
+++ b/cmstestsuite/browser_tests/submissions_test.py
@@ -0,0 +1,116 @@
+#!/usr/bin/env python3
+
+# Contest Management System - http://cms-dev.github.io/
+# Copyright © 2026 Pasit Sangprachathanarak <ouipingpasit@gmail.com>
+#
+# This program is free software: you can redistribute it and/or modify
+# it under the terms of the GNU Affero General Public License as
+# published by the Free Software Foundation, either version 3 of the
+# License, or (at your option) any later version.
+#
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU Affero General Public License for more details.
+#
+# You should have received a copy of the GNU Affero General Public License
+# along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
+"""Browser tests for the submissions page: listing, details dialog,
+download, tokens and sending a new submission."""
+
+from playwright.sync_api import expect
+
+from cmstestsuite.browser_tests import seed
+
+
+ROWS = ".submission_list tbody tr[data-submission]"
+
+
+def open_submissions(page, base_url):
+    page.goto("%stasks/%s/submissions" % (base_url, seed.TASK_NAME))
+
+
+def test_submission_list_shows_seeded_results(page, base_url, login, seeded):
+    login(seed.READER)
+    open_submissions(page, base_url)
+    rows = page.locator(ROWS)
+    expect(rows).to_have_count(seeded.reader_submissions)
+    expect(rows.first).to_contain_text("50 / 50")
+
+
+def test_no_submissions_is_an_empty_list(page, base_url, login):
+    login(seed.NOBODY)
+    open_submissions(page, base_url)
+    expect(page.locator(ROWS)).to_have_count(0)
+
+
+def test_submission_details_open_in_a_dialog(page, base_url, login):
+    login(seed.READER)
+    open_submissions(page, base_url)
+    dialog = page.locator("#submission_detail")
+    expect(dialog).to_be_hidden()
+
+    page.get_by_text("details", exact=True).first.click()
+    expect(dialog).to_be_visible()
+    expect(dialog.get_by_text("Output is correct")).to_be_visible()
+
+    dialog.get_by_text("Close", exact=True).click()
+    expect(dialog).to_be_hidden()
+
+
+def test_submission_details_close_with_the_x(page, base_url, login):
+    login(seed.READER)
+    open_submissions(page, base_url)
+    page.get_by_text("details", exact=True).first.click()
+    dialog = page.locator("#submission_detail")
+    expect(dialog).to_be_visible()
+    # The footer's "Close" may be a link or a button; the x comes first.
+    dialog.get_by_role("button", name="Close").first.click()
+    expect(dialog).to_be_hidden()
+
+
+def test_download_submitted_file(page, base_url, login):
+    login(seed.READER)
+    open_submissions(page, base_url)
+    with page.expect_download() as info:
+        page.get_by_role("link", name="Download").first.click()
+    assert info.value.suggested_filename == "sum.py"
+
+
+def test_play_a_token(page, base_url, login):
+    login(seed.TOKEN_USER)
+    open_submissions(page, base_url)
+    play = page.get_by_role("button", name="Play!")
+    before = play.count()
+    assert before >= 1
+    play.first.click()
+    page.wait_for_load_state("networkidle")
+    open_submissions(page, base_url)
+    expect(page.get_by_text("Played", exact=True)).to_have_count(1)
+    expect(page.get_by_role("button", name="Play!")).to_have_count(before - 1)
+
+
+def test_submit_a_solution(page, base_url, login, tmp_path):
+    login(seed.SUBMITTER)
+    open_submissions(page, base_url)
+    expect(page.locator(ROWS)).to_have_count(0)
+
+    source = tmp_path / "sum.py"
+    source.write_text("print(sum(map(int, input().split())))\n")
+    page.set_input_files("input[type=file][name='sum.%l']", str(source))
+    page.locator("select[name=language]").select_option(
+        label="Python 3 / CPython")
+    page.get_by_role("button", name="Submit").first.click()
+
+    # The submission is listed; it stays unevaluated since no evaluation
+    # service runs in the browser tests.
+    expect(page.locator(ROWS)).to_have_count(1)
+
+
+def test_submit_nothing_creates_no_submission(page, base_url, login):
+    login(seed.ASKER)
+    open_submissions(page, base_url)
+    page.get_by_role("button", name="Submit").first.click()
+    open_submissions(page, base_url)
+    expect(page.locator(ROWS)).to_have_count(0)
diff --git a/cmstestsuite/browser_tests/testing_test.py b/cmstestsuite/browser_tests/testing_test.py
new file mode 100644
index 0000000000..1b890cefe8
--- /dev/null
+++ b/cmstestsuite/browser_tests/testing_test.py
@@ -0,0 +1,109 @@
+#!/usr/bin/env python3
+
+# Contest Management System - http://cms-dev.github.io/
+# Copyright © 2026 Pasit Sangprachathanarak <ouipingpasit@gmail.com>
+#
+# This program is free software: you can redistribute it and/or modify
+# it under the terms of the GNU Affero General Public License as
+# published by the Free Software Foundation, either version 3 of the
+# License, or (at your option) any later version.
+#
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU Affero General Public License for more details.
+#
+# You should have received a copy of the GNU Affero General Public License
+# along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
+"""Browser tests for the testing page, which has one tab per task, a
+details dialog and download menus."""
+
+import pytest
+from playwright.sync_api import expect
+
+from cmstestsuite.browser_tests import seed
+
+
+@pytest.fixture
+def testing(page, base_url, login):
+    login(seed.READER)
+    page.goto(base_url + "testing")
+    return page
+
+
+def test_tabs_switch_between_tasks(testing):
+    sum_pane = testing.locator("#test_%s" % seed.TASK_NAME)
+    pair_pane = testing.locator("#test_%s" % seed.PAIR_TASK_NAME)
+    expect(sum_pane).to_be_visible()
+    expect(pair_pane).to_be_hidden()
+
+    testing.get_by_role("link", name=seed.PAIR_TASK_NAME, exact=True).click()
+    expect(pair_pane).to_be_visible()
+    expect(sum_pane).to_be_hidden()
+
+    testing.get_by_role("link", name=seed.TASK_NAME, exact=True).click()
+    expect(sum_pane).to_be_visible()
+    expect(pair_pane).to_be_hidden()
+
+
+def test_previous_tests_are_listed(testing):
+    rows = testing.locator("#test_%s tr[data-user-test]" % seed.TASK_NAME)
+    expect(rows).to_have_count(1)
+    expect(rows.first).to_contain_text("Executed")
+
+
+def test_test_details_open_in_a_dialog(testing):
+    dialog = testing.locator("#user_test_detail")
+    expect(dialog).to_be_hidden()
+
+    testing.get_by_text("details", exact=True).first.click()
+    expect(dialog).to_be_visible()
+    expect(dialog.get_by_text("Execution completed successfully")) \
+        .to_be_visible()
+
+    dialog.get_by_text("Close", exact=True).click()
+    expect(dialog).to_be_hidden()
+
+
+def test_test_details_close_with_the_x(testing):
+    testing.get_by_text("details", exact=True).first.click()
+    dialog = testing.locator("#user_test_detail")
+    expect(dialog).to_be_visible()
+    # The footer's "Close" may be a link or a button; the x comes first.
+    dialog.get_by_role("button", name="Close").first.click()
+    expect(dialog).to_be_hidden()
+
+
+def test_multi_file_test_has_a_download_menu(testing):
+    testing.get_by_role("link", name=seed.PAIR_TASK_NAME, exact=True).click()
+    pane = testing.locator("#test_%s" % seed.PAIR_TASK_NAME)
+    first, second = seed.PAIR_FILES
+    item = pane.get_by_role("link", name=first)
+    expect(item).to_be_hidden()
+
+    pane.locator("tr[data-user-test] td.files") \
+        .get_by_text("Download", exact=True).click()
+    expect(item).to_be_visible()
+    expect(pane.get_by_role("link", name=second)).to_be_visible()
+
+    with testing.expect_download() as info:
+        item.click()
+    assert info.value.suggested_filename == first
+
+
+def test_single_file_test_has_a_direct_download_link(testing):
+    pane = testing.locator("#test_%s" % seed.TASK_NAME)
+    link = pane.locator("tr[data-user-test] td.files") \
+        .get_by_role("link", name="Download")
+    with testing.expect_download() as info:
+        link.click()
+    assert info.value.suggested_filename == "sum.py"
+
+
+def test_submit_test_form_has_file_inputs_and_language(testing):
+    pane = testing.locator("#test_%s" % seed.TASK_NAME)
+    expect(pane.get_by_role("heading", name="Submit a test")).to_be_visible()
+    expect(pane.locator("input[type=file][name='sum.%l']")).to_be_visible()
+    expect(pane.locator("input[type=file][name=input]")).to_be_visible()
+    expect(pane.locator("select[name=language]")).to_be_visible()
diff --git a/docker/_cms-browser-test-internal.sh b/docker/_cms-browser-test-internal.sh
new file mode 100755
index 0000000000..82fa5305e7
--- /dev/null
+++ b/docker/_cms-browser-test-internal.sh
@@ -0,0 +1,6 @@
+#!/usr/bin/env bash
+
+dropdb --if-exists --host=testdb --username=postgres cmsdbfortesting
+createdb --host=testdb --username=postgres cmsdbfortesting
+
+pytest cmstestsuite/browser_tests
diff --git a/docker/cms-browser-test.sh b/docker/cms-browser-test.sh
new file mode 100755
index 0000000000..24fceed9a4
--- /dev/null
+++ b/docker/cms-browser-test.sh
@@ -0,0 +1,6 @@
+#!/usr/bin/env bash
+set -x
+
+GIT_BRANCH_NAME=$(git rev-parse --abbrev-ref HEAD | tr A-Z a-z)
+
+docker compose -p cms-$GIT_BRANCH_NAME -f docker/docker-compose.test.yml run --build --rm browsertestcms
diff --git a/docker/docker-compose.test.yml b/docker/docker-compose.test.yml
index 72048c2410..9d50ffaaa6 100644
--- a/docker/docker-compose.test.yml
+++ b/docker/docker-compose.test.yml
@@ -20,6 +20,17 @@ services:
     cgroup: host
     command: wait-for-it testdb:5432 -- docker/_cms-test-internal.sh
 
+  browsertestcms:
+    build: ..
+    depends_on:
+      - "testdb"
+    environment:
+      CMS_CONFIG: /home/cmsuser/cms/etc/cms-testdb.toml
+      PYTEST_ADDOPTS: --color=yes
+    privileged: true
+    cgroup: host
+    command: wait-for-it testdb:5432 -- docker/_cms-browser-test-internal.sh
+
   stresstestcms:
     build: ..
     depends_on:
diff --git a/docs/Docker image.rst b/docs/Docker image.rst
index 38ea8f4958..2d2e5e6cae 100644
--- a/docs/Docker image.rst	
+++ b/docs/Docker image.rst	
@@ -15,6 +15,13 @@ dependencies. We also provide:
      users logging in via ContestWebServer and repeatedly performing actions
      such as download task statements and submitting solutions.
 
+* :gh_blob:`docker/cms-browser-test.sh`: Similar to ``cms-test.sh`` but runs the
+     browser tests instead of the unit and functional tests. The browser tests
+     start a ContestWebServer on a database filled with sample data, and drive
+     it with a real browser (Chromium, through Playwright) to check that the
+     contestant pages work, including their JavaScript. See
+     :ref:`docker-image_running-browser-tests`.
+
 * :gh_blob:`docker/cms-dev.sh`: This file uses :gh_blob:`docker/docker-compose.dev.yml` to
      spawn a database (**persisted** in the local ``.dev/postgres-data`` folder
      within the repository) as well as a CMS container that only runs ``bash``,
@@ -84,6 +91,50 @@ To delete the ``cms-testdb-1`` container after testing you can run:
 
     docker rm -f cms-testdb-1
 
+.. _docker-image_running-browser-tests:
+
+Running browser tests
+---------------------
+
+The browser tests (in :gh_blob:`cmstestsuite/browser_tests`) are not part of the
+command above. Run them with:
+
+.. sourcecode:: bash
+
+    docker/cms-browser-test.sh
+
+or, with the full command:
+
+.. sourcecode:: bash
+
+    docker compose -p someprojectname -f docker/docker-compose.test.yml run --build --rm browsertestcms
+
+The same notes about ``-p``, ``sudo`` and cleaning up the database container
+apply as above.
+
+The tests recreate the test database, fill it with a small contest (a few users,
+two tasks, already evaluated submissions, an announcement, and so on), start a
+ContestWebServer on it and then open its pages in a browser. They do not start
+any evaluation service, so submissions made during the tests are never graded.
+A test fails if a page logs a JavaScript error or fails to load one of its
+static files. Tests look for elements by their role, label or text and not by
+CSS class, so that they keep working when the front-end framework changes.
+
+If you want to run them without Docker, install the extra dependencies, download
+the browser, point ``CMS_CONFIG`` to a configuration whose database name ends
+with ``fortesting`` (the tests refuse to run on any other database, since they
+delete its content), and run pytest on the directory:
+
+.. sourcecode:: bash
+
+    pip install ".[browser-test]"
+    playwright install chromium
+    pytest cmstestsuite/browser_tests
+
+Plain ``pytest`` does not collect them. To watch the browser, add ``--headed``;
+to see the output of the ContestWebServer used by the tests, set the
+``CMS_BROWSER_TEST_VERBOSE`` environment variable.
+
 Developing CMS
 ==============
 
diff --git a/docs/Installation.rst b/docs/Installation.rst
index 92bc1b1a62..6c5f870b31 100644
--- a/docs/Installation.rst
+++ b/docs/Installation.rst
@@ -158,6 +158,9 @@ If you want to develop CMS, you can use :samp:`./install.py --dir={install_dir}
 This includes development dependencies. It also makes the installation linked to the
 source directory, so you don't need to reinstall if you edit the source.
 
+The browser tests need some more dependencies, which are not installed by
+``--devel``; see :ref:`docker-image_running-browser-tests`.
+
 
 Configuring the worker machines
 ===============================
diff --git a/pyproject.toml b/pyproject.toml
index 7cabb1ba1e..5969ddcf58 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -64,6 +64,11 @@ devel = [
     # "Sphinx>=1.8,<1.9",
 ]
 
+# Only for the browser tests in cmstestsuite/browser_tests.
+browser-test = [
+    "pytest-playwright>=0.5,<1",
+]
+
 [build-system]
 requires = ["setuptools==82.0.0", "babel==2.12.1"]
 build-backend = "setuptools.build_meta"