diff --git a/Libraries/LibHTTP/CMakeLists.txt b/Libraries/LibHTTP/CMakeLists.txt
index 3a4f1c0eaa..7efb10bac8 100644
--- a/Libraries/LibHTTP/CMakeLists.txt
+++ b/Libraries/LibHTTP/CMakeLists.txt
@@ -15,5 +15,8 @@ set(SOURCES
     Method.cpp
 )
 
+include(hsts_preload)
+list(APPEND SOURCES ${HSTS_PRELOAD_SOURCES})
+
 ladybird_lib(LibHTTP http)
 target_link_libraries(LibHTTP PRIVATE LibCompress LibCore LibCrypto LibDatabase LibFileSystem LibIPC LibRegex LibTextCodec LibTLS LibUnicode LibURL)
diff --git a/Libraries/LibWeb/Fetch/Fetching/Fetching.cpp b/Libraries/LibWeb/Fetch/Fetching/Fetching.cpp
index 380af54c89..f17d04f75a 100644
--- a/Libraries/LibWeb/Fetch/Fetching/Fetching.cpp
+++ b/Libraries/LibWeb/Fetch/Fetching/Fetching.cpp
@@ -456,7 +456,7 @@ GC::Ptr<PendingResponse> main_fetch(JS::Realm& realm, Infrastructure::FetchParam
         // - Matching request’s current URL’s host per Known HSTS Host Domain Name Matching results in either a
         //   superdomain match with an asserted includeSubDomains directive or a congruent match (with or without an
         //   asserted includeSubDomains directive) [HSTS]
-        && Bindings::principal_host_defined_page(realm).client().page_did_is_known_hsts_host(request->current_url().host()->get<String>())
+        && ResourceLoader::is_known_hsts_host(Bindings::principal_host_defined_page(realm), request->current_url().host()->get<String>())
         // FIXME: or DNS resolution for the request finds a matching HTTPS RR per section 9.5 of [SVCB].
     ) {
         request->current_url().set_scheme("https"_string);
diff --git a/Libraries/LibWeb/Internals/Internals.cpp b/Libraries/LibWeb/Internals/Internals.cpp
index 86d4344096..0fd6fc3274 100644
--- a/Libraries/LibWeb/Internals/Internals.cpp
+++ b/Libraries/LibWeb/Internals/Internals.cpp
@@ -568,7 +568,7 @@ void Internals::ingest_hsts_header(String const& url, String const& header_value
 
 bool Internals::is_known_hsts_host(String const& domain)
 {
-    return page().client().page_did_is_known_hsts_host(domain);
+    return ResourceLoader::is_known_hsts_host(page(), domain);
 }
 
 void Internals::set_browser_zoom(double factor)
diff --git a/Libraries/LibWeb/Loader/ResourceLoader.cpp b/Libraries/LibWeb/Loader/ResourceLoader.cpp
index a457bcc72e..ffb3abb8cc 100644
--- a/Libraries/LibWeb/Loader/ResourceLoader.cpp
+++ b/Libraries/LibWeb/Loader/ResourceLoader.cpp
@@ -14,6 +14,7 @@
 #include <LibHTTP/Cookie/Cookie.h>
 #include <LibHTTP/Cookie/ParsedCookie.h>
 #include <LibHTTP/HSTS/ParsedHSTSPolicy.h>
+#include <LibHTTP/HSTSPreloadData.h>
 #include <LibRequests/Request.h>
 #include <LibRequests/RequestClient.h>
 #include <LibURL/Parser.h>
@@ -139,6 +140,15 @@ void ResourceLoader::try_store_hsts_policy_for_url(Page& page, URL::URL const& u
     page.client().page_did_store_hsts_policy(url.host()->get<String>(), parsed_policy.value());
 }
 
+// https://www.rfc-editor.org/rfc/rfc6797#section-8.2
+bool ResourceLoader::is_known_hsts_host(Page& page, String const& host)
+{
+    if (HTTP::HSTSPreloadData::the().is_known_preloaded_hsts_host(host.to_ascii_lowercase()))
+        return true;
+
+    return page.client().page_did_is_known_hsts_host(host);
+}
+
 static NonnullRefPtr<HTTP::HeaderList> response_headers_for_file(StringView path, Optional<time_t> const& modified_time)
 {
     // For file:// and resource:// URLs, we have to guess the MIME type, since there's no HTTP header to tell us what
diff --git a/Libraries/LibWeb/Loader/ResourceLoader.h b/Libraries/LibWeb/Loader/ResourceLoader.h
index 46bb633376..bfc4be2e27 100644
--- a/Libraries/LibWeb/Loader/ResourceLoader.h
+++ b/Libraries/LibWeb/Loader/ResourceLoader.h
@@ -50,6 +50,7 @@ public:
     int pending_loads() const { return m_pending_loads; }
 
     static void try_store_hsts_policy_for_url(Page&, URL::URL const&, StringView header_value);
+    static bool is_known_hsts_host(Page&, String const& host);
 
     String const& user_agent() const { return m_user_agent; }
     void set_user_agent(String user_agent) { m_user_agent = move(user_agent); }
diff --git a/Tests/LibHTTP/CMakeLists.txt b/Tests/LibHTTP/CMakeLists.txt
index fd6b3adbc6..f1d956e714 100644
--- a/Tests/LibHTTP/CMakeLists.txt
+++ b/Tests/LibHTTP/CMakeLists.txt
@@ -1,6 +1,7 @@
 set(TEST_SOURCES
     TestCacheUtilities.cpp
     TestHSTSPolicy.cpp
+    TestHSTSPreloadData.cpp
     TestHTTPUtils.cpp
 )
 
diff --git a/Tests/LibHTTP/TestHSTSPreloadData.cpp b/Tests/LibHTTP/TestHSTSPreloadData.cpp
new file mode 100644
index 0000000000..7bd93069d5
--- /dev/null
+++ b/Tests/LibHTTP/TestHSTSPreloadData.cpp
@@ -0,0 +1,33 @@
+/*
+ * Copyright (c) 2026, Luke Wilde <luke@ladybird.org>
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#include <LibHTTP/HSTSPreloadData.h>
+#include <LibTest/TestCase.h>
+
+// Hosts from Chromium's transport_security_state_static.json:
+//  - accounts.google.com: a preloaded force-https host (exact match).
+//  - dev: a force-https TLD with include_subdomains, so any *.dev matches as a subdomain.
+//  - example.test: a reserved TLD that is never preloaded.
+// Stable enough to anchor tests; if upstream removes one the matching test fails loudly
+// rather than silently regressing.
+//
+// is_known_preloaded_hsts_host expects an already-lowercased domain (callers canonicalize
+// before querying), so these tests pass lowercased input.
+
+TEST_CASE(congruent_match)
+{
+    EXPECT(HTTP::HSTSPreloadData::the().is_known_preloaded_hsts_host("accounts.google.com"sv));
+}
+
+TEST_CASE(subdomain_match_via_include_subdomains)
+{
+    EXPECT(HTTP::HSTSPreloadData::the().is_known_preloaded_hsts_host("anything.dev"sv));
+}
+
+TEST_CASE(non_preloaded_host_is_not_known)
+{
+    EXPECT(!HTTP::HSTSPreloadData::the().is_known_preloaded_hsts_host("example.test"sv));
+}
diff --git a/Tests/LibWeb/Text/expected/HSTS/hsts-preload.txt b/Tests/LibWeb/Text/expected/HSTS/hsts-preload.txt
new file mode 100644
index 0000000000..7ef22e9a43
--- /dev/null
+++ b/Tests/LibWeb/Text/expected/HSTS/hsts-preload.txt
@@ -0,0 +1 @@
+PASS
diff --git a/Tests/LibWeb/Text/input/HSTS/hsts-preload.html b/Tests/LibWeb/Text/input/HSTS/hsts-preload.html
new file mode 100644
index 0000000000..6e2bb6d3da
--- /dev/null
+++ b/Tests/LibWeb/Text/input/HSTS/hsts-preload.html
@@ -0,0 +1,35 @@
+<!DOCTYPE html>
+<script src="../include.js"></script>
+<script>
+    // Test the built-in HSTS preload list: known hosts and subdomains report as HSTS-known on
+    // a fresh profile, unknown hosts do not, and a max-age=0 response cannot override preload.
+    test(() => {
+        // Hosts from Chromium's transport_security_state_static.json:
+        //  - accounts.google.com: a preloaded force-https host (exact-match coverage).
+        //  - dev: a force-https TLD with include_subdomains, so any *.dev is a subdomain match.
+        //  - paypal.com: a preloaded force-https host, used for the max-age=0 override check.
+        if (!internals.isKnownHSTSHost("accounts.google.com")) {
+            println("FAIL - preloaded host should be HSTS-known");
+            return;
+        }
+
+        if (!internals.isKnownHSTSHost("anything.dev")) {
+            println("FAIL - subdomain of preloaded include_subdomains TLD should be HSTS-known");
+            return;
+        }
+
+        if (internals.isKnownHSTSHost("example.test")) {
+            println("FAIL - non-preloaded host should not be HSTS-known on a fresh profile");
+            return;
+        }
+
+        // max-age=0 from a preloaded host must not unset its preload bit.
+        internals.setHSTSPolicy("paypal.com", 0, false);
+        if (!internals.isKnownHSTSHost("paypal.com")) {
+            println("FAIL - max-age=0 should not override the preload list");
+            return;
+        }
+
+        println("PASS");
+    });
+</script>
diff --git a/Tests/LibWebView/CMakeLists.txt b/Tests/LibWebView/CMakeLists.txt
index 12fcd1eeb8..6fa2f05a7d 100644
--- a/Tests/LibWebView/CMakeLists.txt
+++ b/Tests/LibWebView/CMakeLists.txt
@@ -1,5 +1,6 @@
 set(TEST_SOURCES
     TestHistoryStore.cpp
+    TestHSTSStore.cpp
     TestWebViewURL.cpp
 )
 
diff --git a/Tests/LibWebView/TestHSTSStore.cpp b/Tests/LibWebView/TestHSTSStore.cpp
new file mode 100644
index 0000000000..d2c3afcb95
--- /dev/null
+++ b/Tests/LibWebView/TestHSTSStore.cpp
@@ -0,0 +1,60 @@
+/*
+ * Copyright (c) 2026, Luke Wilde <luke@ladybird.org>
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#include <AK/NonnullOwnPtr.h>
+#include <AK/Time.h>
+#include <LibHTTP/HSTS/ParsedHSTSPolicy.h>
+#include <LibTest/TestCase.h>
+#include <LibWebView/HSTSStore.h>
+
+// HSTSStore is the dynamic, per-profile store only; the built-in preload list is consulted
+// separately at the fetch layer (see Tests/LibHTTP/TestHSTSPreloadData.cpp). These tests use
+// example.test, which is not a preloaded host, so they exercise the dynamic store in isolation.
+
+TEST_CASE(congruent_match)
+{
+    auto store = WebView::HSTSStore::create();
+    store->store_policy("example.test"_string, HTTP::HSTS::ParsedHSTSPolicy { AK::Duration::from_seconds(3600), false });
+    EXPECT(store->is_known_hsts_host("example.test"sv));
+}
+
+TEST_CASE(superdomain_match_via_include_subdomains)
+{
+    auto store = WebView::HSTSStore::create();
+    store->store_policy("example.test"_string, HTTP::HSTS::ParsedHSTSPolicy { AK::Duration::from_seconds(3600), true });
+    EXPECT(store->is_known_hsts_host("sub.example.test"sv));
+}
+
+TEST_CASE(superdomain_not_matched_without_include_subdomains)
+{
+    auto store = WebView::HSTSStore::create();
+    store->store_policy("example.test"_string, HTTP::HSTS::ParsedHSTSPolicy { AK::Duration::from_seconds(3600), false });
+    EXPECT(!store->is_known_hsts_host("sub.example.test"sv));
+}
+
+TEST_CASE(unknown_host_is_not_hsts_known)
+{
+    auto store = WebView::HSTSStore::create();
+    EXPECT(!store->is_known_hsts_host("example.test"sv));
+}
+
+TEST_CASE(max_age_zero_removes_dynamic_policy)
+{
+    auto store = WebView::HSTSStore::create();
+    store->store_policy("example.test"_string, HTTP::HSTS::ParsedHSTSPolicy { AK::Duration::from_seconds(3600), false });
+    EXPECT(store->is_known_hsts_host("example.test"sv));
+
+    store->store_policy("example.test"_string, HTTP::HSTS::ParsedHSTSPolicy { AK::Duration::zero(), false });
+    EXPECT(!store->is_known_hsts_host("example.test"sv));
+}
+
+TEST_CASE(remove_policies_observed_since_clears_dynamic_data)
+{
+    auto store = WebView::HSTSStore::create();
+    store->store_policy("example.test"_string, HTTP::HSTS::ParsedHSTSPolicy { AK::Duration::from_seconds(3600), false });
+    store->remove_policies_observed_since(UnixDateTime::earliest());
+    EXPECT(!store->is_known_hsts_host("example.test"sv));
+}