diff --git a/src/browser/Session.zig b/src/browser/Session.zig
index 4c9cda141..64c4b43a4 100644
--- a/src/browser/Session.zig
+++ b/src/browser/Session.zig
@@ -25,6 +25,7 @@ const Config = @import("../Config.zig");
 const History = @import("webapi/History.zig");
 const storage = @import("webapi/storage/storage.zig");
 const IdbManager = @import("webapi/storage/idb/idb.zig").Manager;
+const CacheStore = @import("webapi/cache/Store.zig");
 const Factory = @import("Factory.zig");
 const EventTarget = @import("webapi/EventTarget.zig");
 const Navigation = @import("webapi/navigation/Navigation.zig");
@@ -53,8 +54,8 @@ arena: *lp.Arena,
 history: History,
 navigation: *Navigation,
 storage_shed: storage.Shed,
-// Per-origin IndexedDB engines
-idb: IdbManager,
+idb: IdbManager, // Per-origin IndexedDB engines
+cache_store: CacheStore, // Per-origin CacheStorage
 // Backs `globalThis.lp.*`; values pre-stringified so the prelude splices
 // them in without re-encoding.
 bridge_store: std.StringHashMapUnmanaged([]const u8) = .empty,
@@ -170,6 +171,7 @@ pub fn init(self: *Session, browser: *Browser, notification: *Notification) !voi
         .navigation = navigation,
         .storage_shed = .{},
         .idb = IdbManager.init(allocator),
+        .cache_store = CacheStore.init(allocator),
         .browser = browser,
         .notification = notification,
         .cookie_jar = storage.Cookie.Jar.init(allocator, notification),
@@ -213,6 +215,7 @@ pub fn deinit(self: *Session) void {
 
     self.storage_shed.deinit(self.browser.app.allocator);
     self.idb.deinit();
+    self.cache_store.deinit();
     {
         const allocator = self.browser.app.allocator;
         var it = self.bridge_store.iterator();
diff --git a/src/browser/js/Env.zig b/src/browser/js/Env.zig
index f0b46ea29..ba8cfb4fa 100644
--- a/src/browser/js/Env.zig
+++ b/src/browser/js/Env.zig
@@ -320,10 +320,8 @@ fn _createContext(self: *Env, global: anytype, params: ContextParams) !*Context
     // Get the global object for the context
     const global_obj = v8.v8__Context__Global(v8_context).?;
 
-    if (comptime is_frame) {
-        if (global._session.experimental_features.serviceworker == false) {
-            self.hideServiceWorker(v8_context, global_obj);
-        }
+    if (global._session.experimental_features.serviceworker == false) {
+        self.hideServiceWorker(is_frame, v8_context, global_obj);
     }
 
     // Store our TAO inside the internal field of the global object. This
@@ -430,17 +428,32 @@ fn _createContext(self: *Env, global: anytype, params: ContextParams) !*Context
 // its own Navigator.prototype (2 Gets + 1 Delete).
 // (If this proves to be an issue, we could swap the logic, and dynamically ADD
 // it when it is enabled, but that's a lot more code).
-fn hideServiceWorker(self: *const Env, v8_context: *const v8.Context, global_obj: *const v8.Object) void {
+fn hideServiceWorker(self: *const Env, comptime is_frame: bool, v8_context: *const v8.Context, global_obj: *const v8.Object) void {
+    if (comptime is_frame) {
+        self.deletePrototypeMember(v8_context, global_obj, "navigator", "service_worker");
+    }
+
+    // A [Global] interface's members are on its prototype and mirrored onto the
+    // global itself.
+    self.deletePrototypeMember(v8_context, global_obj, if (comptime is_frame) "window" else "worker_global_scope", "caches");
+    var deleted: v8.MaybeBool = undefined;
+    v8.v8__Object__Delete(global_obj, v8_context, @ptrCast(self.disabled_api_names.get(self.isolate.handle, "caches")), &deleted);
+    if (deleted.has_value == false or deleted.value == false) {
+        log.warn(.js, "failed to hide experimental API", .{ .interface = "global", .member = "caches" });
+    }
+}
+
+fn deletePrototypeMember(self: *const Env, v8_context: *const v8.Context, global_obj: *const v8.Object, comptime interface: []const u8, comptime member: []const u8) void {
     const isolate = self.isolate.handle;
     const names = &self.disabled_api_names;
 
-    const constructor = v8.v8__Object__Get(global_obj, v8_context, @ptrCast(names.get(isolate, "navigator"))) orelse return;
+    const constructor = v8.v8__Object__Get(global_obj, v8_context, @ptrCast(names.get(isolate, interface))) orelse return;
     const prototype = v8.v8__Object__Get(@ptrCast(constructor), v8_context, @ptrCast(names.get(isolate, "prototype"))) orelse return;
 
     var deleted: v8.MaybeBool = undefined;
-    v8.v8__Object__Delete(@ptrCast(prototype), v8_context, @ptrCast(names.get(isolate, "service_worker")), &deleted);
+    v8.v8__Object__Delete(@ptrCast(prototype), v8_context, @ptrCast(names.get(isolate, member)), &deleted);
     if (deleted.has_value == false or deleted.value == false) {
-        log.warn(.js, "failed to hide navigator.serviceWorker", .{});
+        log.warn(.js, "failed to hide experimental API", .{ .interface = interface, .member = member });
     }
 }
 
@@ -756,14 +769,20 @@ fn oomCallback(c_location: [*c]const u8, details: ?*const v8.OOMDetails) callcon
 
 const DisabledApiNames = struct {
     navigator: v8.Eternal,
+    window: v8.Eternal,
+    worker_global_scope: v8.Eternal,
     prototype: v8.Eternal,
     service_worker: v8.Eternal,
+    caches: v8.Eternal,
 
     fn init(isolate: *v8.Isolate) DisabledApiNames {
         var self: DisabledApiNames = undefined;
         intern(isolate, &self.navigator, "Navigator");
+        intern(isolate, &self.window, "Window");
+        intern(isolate, &self.worker_global_scope, "WorkerGlobalScope");
         intern(isolate, &self.prototype, "prototype");
         intern(isolate, &self.service_worker, "serviceWorker");
+        intern(isolate, &self.caches, "caches");
         return self;
     }
 
diff --git a/src/browser/js/bridge.zig b/src/browser/js/bridge.zig
index 95dbe17c2..1098779c7 100644
--- a/src/browser/js/bridge.zig
+++ b/src/browser/js/bridge.zig
@@ -1227,6 +1227,8 @@ pub const PageJsApis = flattenTypes(&.{
     @import("../webapi/storage/storage.zig"),
     @import("../webapi/storage/CookieStore.zig"),
     @import("../webapi/storage/idb/idb.zig"),
+    @import("../webapi/cache/CacheStorage.zig"),
+    @import("../webapi/cache/Cache.zig"),
     @import("../webapi/event/CookieChangeEvent.zig"),
     @import("../webapi/URL.zig"),
     @import("../webapi/URLPattern.zig"),
@@ -1342,6 +1344,8 @@ const worker_common_apis = [_]type{
     @import("../webapi/Performance.zig"),
     @import("../webapi/PerformanceObserver.zig"),
     @import("../webapi/storage/idb/idb.zig"),
+    @import("../webapi/cache/CacheStorage.zig"),
+    @import("../webapi/cache/Cache.zig"),
     @import("../webapi/BroadcastChannel.zig"),
     @import("../webapi/event/CustomEvent.zig"),
     @import("../webapi/event/ProgressEvent.zig"),
diff --git a/src/browser/tests/cache/cache.html b/src/browser/tests/cache/cache.html
new file mode 100644
index 000000000..654a141a7
--- /dev/null
+++ b/src/browser/tests/cache/cache.html
@@ -0,0 +1,236 @@
+<!DOCTYPE html>
+<script src="../testing.js"></script>
+
+<script id=cache_storage type=module>
+  const state = await testing.async();
+
+  testing.expectTrue('caches' in window);
+  testing.expectTrue(caches instanceof CacheStorage);
+  testing.expectTrue(caches === window.caches);
+
+  await caches.delete('cs-a');
+  await caches.delete('cs-b');
+
+  const before = await caches.has('cs-a');
+  const a = await caches.open('cs-a');
+  await caches.open('cs-b');
+  const after = await caches.has('cs-a');
+  const names = await caches.keys();
+
+  const deleted = await caches.delete('cs-a');
+  const deleted_again = await caches.delete('cs-a');
+  const gone = await caches.has('cs-a');
+
+  // A Cache outlives its name.
+  await a.put('/orphan', new Response('orphan'));
+  const orphan = await (await a.match('/orphan')).text();
+  const unreachable = await caches.match('/orphan');
+
+  state.resolve();
+  await state.done(() => {
+    testing.expectEqual(false, before);
+    testing.expectTrue(a instanceof Cache);
+    testing.expectEqual(true, after);
+    // creation order
+    testing.expectTrue(names.indexOf('cs-a') >= 0);
+    testing.expectEqual(names.indexOf('cs-a') + 1, names.indexOf('cs-b'));
+    testing.expectEqual(true, deleted);
+    testing.expectEqual(false, deleted_again);
+    testing.expectEqual(false, gone);
+    testing.expectEqual('orphan', orphan);
+    testing.expectEqual(undefined, unreachable);
+  });
+</script>
+
+<script id=put_match type=module>
+  const state = await testing.async();
+
+  await caches.delete('put-match');
+  const cache = await caches.open('put-match');
+
+  const miss = await cache.match('/nope');
+
+  const stored = new Response('hello', {
+    status: 201,
+    statusText: 'Created',
+    headers: { 'Content-Type': 'text/x-test', 'X-Custom': 'abc' },
+  });
+  const put_result = await cache.put('/a?x=1#frag', stored);
+
+  const hit = await cache.match(new Request('/a?x=1'));
+  const hit_text = await hit.text();
+  // every match is a new Response, with its own body
+  const hit2 = await cache.match('/a?x=1#other');
+  const hit2_text = await hit2.text();
+
+  const no_search = await cache.match('/a');
+  const ignore_search = await cache.match('/a?y=2', { ignoreSearch: true });
+  const post = await cache.match(new Request('/a?x=1', { method: 'POST' }));
+
+  // put replaces
+  await cache.put('/a?x=1', new Response('replaced'));
+  const replaced = await (await cache.match('/a?x=1')).text();
+  const keys = await cache.keys();
+
+  let immutable = null;
+  try {
+    hit.headers.set('x-custom', 'nope');
+  } catch (e) {
+    immutable = e;
+  }
+
+  state.resolve();
+  await state.done(() => {
+    testing.expectEqual(undefined, miss);
+    testing.expectEqual(undefined, put_result);
+    testing.expectEqual(true, stored.bodyUsed);
+
+    testing.expectTrue(hit instanceof Response);
+    testing.expectEqual(201, hit.status);
+    testing.expectEqual('Created', hit.statusText);
+    testing.expectEqual('text/x-test', hit.headers.get('content-type'));
+    testing.expectEqual('abc', hit.headers.get('x-custom'));
+    testing.expectTrue(immutable instanceof TypeError);
+    testing.expectEqual('hello', hit_text);
+    testing.expectTrue(hit !== hit2);
+    testing.expectEqual('hello', hit2_text);
+
+    testing.expectEqual(undefined, no_search);
+    testing.expectTrue(ignore_search instanceof Response);
+    testing.expectEqual(undefined, post);
+
+    testing.expectEqual('replaced', replaced);
+    testing.expectEqual(1, keys.length);
+    testing.expectTrue(keys[0] instanceof Request);
+    testing.expectEqual('GET', keys[0].method);
+    testing.expectTrue(keys[0].url.endsWith('/a?x=1'));
+  });
+</script>
+
+<script id=put_rejects type=module>
+  const state = await testing.async();
+
+  await caches.delete('put-rejects');
+  const cache = await caches.open('put-rejects');
+
+  async function rejection(promise) {
+    try {
+      await promise;
+      return null;
+    } catch (e) {
+      return e;
+    }
+  }
+
+  const used = new Response('used');
+  await used.text();
+
+  const errors = [
+    await rejection(cache.put(new Request('/p', { method: 'POST', body: 'x' }), new Response('x'))),
+    await rejection(cache.put('data:text/plain,x', new Response('x'))),
+    await rejection(cache.put('/p', new Response('x', { status: 206 }))),
+    await rejection(cache.put('/p', new Response('x', { headers: { Vary: 'Accept, *' } }))),
+    await rejection(cache.put('/p', used)),
+  ];
+  const vary_ok = await rejection(cache.put('/p', new Response('x', { headers: { Vary: 'Accept' } })));
+
+  state.resolve();
+  await state.done(() => {
+    testing.expectEqual('TypeError,TypeError,TypeError,TypeError,TypeError', errors.map((e) => e && e.name).join(','));
+    testing.expectEqual(null, vary_ok);
+  });
+</script>
+
+<script id=delete type=module>
+  const state = await testing.async();
+
+  await caches.delete('delete');
+  const cache = await caches.open('delete');
+  await cache.put('/d?x=1', new Response('1'));
+  await cache.put('/d?x=2', new Response('2'));
+  await cache.put('/other', new Response('3'));
+
+  const miss = await cache.delete('/d');
+  const one = await cache.delete('/d?x=1');
+  const after_one = (await cache.keys()).length;
+  await cache.put('/d?x=1', new Response('1'));
+  const all = await cache.delete('/d', { ignoreSearch: true });
+  const keys = await cache.keys();
+
+  state.resolve();
+  await state.done(() => {
+    testing.expectEqual(false, miss);
+    testing.expectEqual(true, one);
+    testing.expectEqual(2, after_one);
+    testing.expectEqual(true, all);
+    testing.expectEqual(1, keys.length);
+    testing.expectTrue(keys[0].url.endsWith('/other'));
+  });
+</script>
+
+<script id=storage_match type=module>
+  const state = await testing.async();
+
+  await caches.delete('sm-1');
+  await caches.delete('sm-2');
+  const one = await caches.open('sm-1');
+  const two = await caches.open('sm-2');
+  await one.put('/sm', new Response('one'));
+  await two.put('/sm', new Response('two'));
+  await two.put('/sm-two', new Response('only two'));
+
+  const first = await (await caches.match('/sm')).text();
+  const named = await (await caches.match('/sm', { cacheName: 'sm-2' })).text();
+  const any = await (await caches.match('/sm-two')).text();
+  const wrong_cache = await caches.match('/sm-two', { cacheName: 'sm-1' });
+  const no_cache = await caches.match('/sm', { cacheName: 'sm-nope' });
+
+  state.resolve();
+  await state.done(() => {
+    testing.expectEqual('one', first);
+    testing.expectEqual('two', named);
+    testing.expectEqual('only two', any);
+    testing.expectEqual(undefined, wrong_cache);
+    testing.expectEqual(undefined, no_cache);
+  });
+</script>
+
+<script id=add type=module>
+  const state = await testing.async();
+
+  await caches.delete('add');
+  const cache = await caches.open('add');
+
+  const added = await cache.add('/xhr/json');
+  const json = await (await cache.match('/xhr/json')).json();
+
+  await cache.addAll(['/xhr', new Request('/xhr/json')]);
+  const count = (await cache.keys()).length;
+  await cache.addAll([]);
+
+  // All or nothing: one 404 and the good one isn't stored either.
+  let not_ok = null;
+  try {
+    await cache.addAll(['/xhr/xml', '/xhr/404']);
+  } catch (e) {
+    not_ok = e;
+  }
+  const xml = await cache.match('/xhr/xml');
+
+  let not_get = null;
+  try {
+    await cache.add(new Request('/xhr', { method: 'POST' }));
+  } catch (e) {
+    not_get = e;
+  }
+
+  state.resolve();
+  await state.done(() => {
+    testing.expectEqual(undefined, added);
+    testing.expectEqual('9000!!!', json.over);
+    testing.expectEqual(2, count);
+    testing.expectTrue(not_ok instanceof TypeError);
+    testing.expectEqual(undefined, xml);
+    testing.expectTrue(not_get instanceof TypeError);
+  });
+</script>
diff --git a/src/browser/tests/cache/disabled-worker.js b/src/browser/tests/cache/disabled-worker.js
new file mode 100644
index 000000000..aa80b5f97
--- /dev/null
+++ b/src/browser/tests/cache/disabled-worker.js
@@ -0,0 +1 @@
+postMessage({ present: 'caches' in self, constructor: typeof CacheStorage });
diff --git a/src/browser/tests/cache/disabled.html b/src/browser/tests/cache/disabled.html
new file mode 100644
index 000000000..a48b6d8ad
--- /dev/null
+++ b/src/browser/tests/cache/disabled.html
@@ -0,0 +1,30 @@
+<!DOCTYPE html>
+<script src="../testing.js"></script>
+
+<script id="caches_absent_without_the_flag">
+  // `caches` rides on --experimental-features serviceworker. Like
+  // navigator.serviceWorker it is absent rather than null, and only the way in
+  // is removed.
+  {
+    testing.expectFalse('caches' in window);
+    testing.expectEqual(undefined, window.caches);
+    testing.expectTrue(typeof CacheStorage === 'function');
+    testing.expectTrue(typeof Cache === 'function');
+  }
+</script>
+
+<script id="caches_absent_in_a_worker" type=module>
+  {
+    const state = await testing.async();
+    const worker = new Worker('./disabled-worker.js');
+    const data = await new Promise((resolve) => {
+      worker.onmessage = (e) => resolve(e.data);
+    });
+
+    state.resolve();
+    await state.done(() => {
+      testing.expectEqual(false, data.present);
+      testing.expectEqual('function', data.constructor);
+    });
+  }
+</script>
diff --git a/src/browser/tests/cache/teardown.html b/src/browser/tests/cache/teardown.html
new file mode 100644
index 000000000..5a9e7a6d1
--- /dev/null
+++ b/src/browser/tests/cache/teardown.html
@@ -0,0 +1,10 @@
+<!DOCTYPE html>
+<script src="../testing.js"></script>
+
+<script id=add_all_in_flight_at_teardown type=module>
+  // Never awaited: the page goes away with one fetch done and one still in
+  // flight. The runner's leak check is the assertion.
+  const cache = await caches.open('teardown');
+  cache.addAll(['/xhr', '/xhr/slow']);
+  testing.expectTrue(true);
+</script>
diff --git a/src/browser/tests/service_worker/cache-worker.js b/src/browser/tests/service_worker/cache-worker.js
new file mode 100644
index 000000000..fcc82e99b
--- /dev/null
+++ b/src/browser/tests/service_worker/cache-worker.js
@@ -0,0 +1,8 @@
+// The canonical install handler: precache, and hold install open until it's
+// done. A throw (no `caches`, a failed fetch) stops the worker before it
+// activates.
+self.addEventListener('install', (e) => {
+  e.waitUntil(
+    caches.open('sw-precache').then((cache) => cache.addAll(['./lifecycle-worker.js', '/xhr/json']))
+  );
+});
diff --git a/src/browser/tests/service_worker/service_worker.html b/src/browser/tests/service_worker/service_worker.html
index d0d793cee..0fbc7d528 100644
--- a/src/browser/tests/service_worker/service_worker.html
+++ b/src/browser/tests/service_worker/service_worker.html
@@ -367,3 +367,27 @@
     });
   }
 </script>
+
+<script id="service_worker_precache" type=module>
+  // What the worker's install handler stored is what the page reads: one
+  // store per origin, shared by both realms.
+  {
+    const state = await testing.async();
+    await caches.delete('sw-precache');
+
+    const reg = await navigator.serviceWorker.register('./cache-worker.js', { scope: './precache/' });
+    await workerReached(reg.installing, 'activated');
+
+    const cache = await caches.open('sw-precache');
+    const keys = await cache.keys();
+    const script = await (await caches.match('./lifecycle-worker.js')).text();
+    const json = await (await cache.match('/xhr/json')).json();
+
+    state.resolve();
+    await state.done(() => {
+      testing.expectEqual(2, keys.length);
+      testing.expectTrue(script.includes("seen.push('install')"));
+      testing.expectEqual('9000!!!', json.over);
+    });
+  }
+</script>
diff --git a/src/browser/webapi/Window.zig b/src/browser/webapi/Window.zig
index 11eabdf57..099a27dd0 100644
--- a/src/browser/webapi/Window.zig
+++ b/src/browser/webapi/Window.zig
@@ -41,9 +41,10 @@ const ErrorEvent = @import("event/ErrorEvent.zig");
 const MessageEvent = @import("event/MessageEvent.zig");
 const MessagePort = @import("MessagePort.zig");
 const MediaQueryList = @import("css/MediaQueryList.zig");
-const storage = @import("storage/storage.zig");
 const idb = @import("storage/idb/idb.zig");
+const storage = @import("storage/storage.zig");
 const CookieStore = @import("storage/CookieStore.zig");
+const CacheStorage = @import("cache/CacheStorage.zig");
 const Element = @import("Element.zig");
 const CSSStyleProperties = @import("css/CSSStyleProperties.zig");
 const CustomElementRegistry = @import("CustomElementRegistry.zig");
@@ -77,6 +78,7 @@ _visual_viewport: *VisualViewport,
 _performance: *Performance,
 _cookie_store: ?*CookieStore = null,
 _idb_factory: ?*idb.IDBFactory = null,
+_caches: ?*CacheStorage = null,
 _on_load: ?js.Function.Global = null,
 _on_pageshow: ?js.Function.Global = null,
 _on_popstate: ?js.Function.Global = null,
@@ -321,6 +323,15 @@ fn getIndexedDB(self: *Window, exec: *Execution) !*idb.IDBFactory {
     return f;
 }
 
+fn getCaches(self: *Window, exec: *Execution) !*CacheStorage {
+    if (self._caches) |c| {
+        return c;
+    }
+    const c = try exec._factory.create(CacheStorage{});
+    self._caches = c;
+    return c;
+}
+
 pub fn getOrigin(self: *const Window) []const u8 {
     return self._frame.origin orelse "null";
 }
@@ -1173,6 +1184,7 @@ pub const JsApi = struct {
     pub const sessionStorage = bridge.accessor(Window.getSessionStorage, null, .{});
     pub const cookieStore = bridge.accessor(Window.getCookieStore, null, .{});
     pub const indexedDB = bridge.accessor(Window.getIndexedDB, null, .{});
+    pub const caches = bridge.accessor(Window.getCaches, null, .{});
     pub const origin = bridge.accessor(Window.getOrigin, Window.setOrigin, .{});
     pub const location = bridge.accessor(Window.getLocation, Window.setLocation, .{ .deletable = false });
     pub const history = bridge.accessor(Window.getHistory, null, .{});
diff --git a/src/browser/webapi/WorkerGlobalScope.zig b/src/browser/webapi/WorkerGlobalScope.zig
index 2bdef5b11..c00b296c3 100644
--- a/src/browser/webapi/WorkerGlobalScope.zig
+++ b/src/browser/webapi/WorkerGlobalScope.zig
@@ -46,6 +46,7 @@ const WorkerLocation = @import("WorkerLocation.zig");
 const ErrorEvent = @import("event/ErrorEvent.zig");
 const Fetch = @import("net/Fetch.zig");
 const idb = @import("storage/idb/idb.zig");
+const CacheStorage = @import("cache/CacheStorage.zig");
 const MessagePort = @import("MessagePort.zig");
 const SharedWorkerGlobalScope = @import("SharedWorkerGlobalScope.zig");
 const ServiceWorkerGlobalScope = @import("ServiceWorkerGlobalScope.zig");
@@ -109,6 +110,7 @@ _crypto: Crypto = .init,
 _navigator: WorkerNavigator = .init,
 _performance: *Performance,
 _idb_factory: ?*idb.IDBFactory = null,
+_caches: ?*CacheStorage = null,
 _on_error: ?JS.Function.Global = null,
 _on_rejection_handled: ?JS.Function.Global = null,
 _on_unhandled_rejection: ?JS.Function.Global = null,
@@ -545,6 +547,15 @@ fn clearInterval(self: *WorkerGlobalScope, id: u32) void {
     self._timers.clear(id);
 }
 
+fn getCaches(self: *WorkerGlobalScope, exec: *JS.Execution) !*CacheStorage {
+    if (self._caches) |c| {
+        return c;
+    }
+    const c = try exec._factory.create(CacheStorage{});
+    self._caches = c;
+    return c;
+}
+
 fn getIndexedDB(self: *WorkerGlobalScope, exec: *JS.Execution) !*idb.IDBFactory {
     if (self._idb_factory) |f| {
         return f;
@@ -600,6 +611,7 @@ pub const JsApi = struct {
     pub const self = bridge.accessor(WorkerGlobalScope.getSelf, WorkerGlobalScope.setSelf, .{});
     pub const location = bridge.accessor(WorkerGlobalScope.getLocation, null, .{});
     pub const indexedDB = bridge.accessor(WorkerGlobalScope.getIndexedDB, null, .{});
+    pub const caches = bridge.accessor(WorkerGlobalScope.getCaches, null, .{});
 
     pub const onerror = bridge.accessor(WorkerGlobalScope.getOnError, WorkerGlobalScope.setOnError, .{});
     pub const onrejectionhandled = bridge.accessor(WorkerGlobalScope.getOnRejectionHandled, WorkerGlobalScope.setOnRejectionHandled, .{});
diff --git a/src/browser/webapi/cache/Cache.zig b/src/browser/webapi/cache/Cache.zig
new file mode 100644
index 000000000..ca26e1551
--- /dev/null
+++ b/src/browser/webapi/cache/Cache.zig
@@ -0,0 +1,371 @@
+// Copyright (C) 2023-2026  Lightpanda (Selecy SAS)
+//
+// Francis Bouvier <francis@lightpanda.io>
+// Pierre Tachoire <pierre@lightpanda.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 <https://www.gnu.org/licenses/>.
+
+const std = @import("std");
+const lp = @import("lightpanda");
+
+const js = @import("../../js/js.zig");
+const URL = @import("../../URL.zig");
+const http = @import("../../../network/http.zig");
+
+const Fetch = @import("../net/Fetch.zig");
+const Headers = @import("../net/Headers.zig");
+const Request = @import("../net/Request.zig");
+const Response = @import("../net/Response.zig");
+
+const Store = @import("Store.zig");
+
+const log = lp.log;
+const Execution = js.Execution;
+const Allocator = std.mem.Allocator;
+
+// Entries are matched on their url alone: no Vary, and only GET is ever stored.
+const Cache = @This();
+
+_origin: *Store.Origin,
+_bucket: *Store.Bucket,
+
+const QueryOptions = struct {
+    ignoreMethod: bool = false, // TODO
+    ignoreSearch: bool = false,
+    ignoreVary: bool = false, // TODO
+};
+
+pub fn init(origin: *Store.Origin, bucket: *Store.Bucket, exec: *const Execution) !*Cache {
+    return exec._factory.create(Cache{ ._origin = origin, ._bucket = bucket });
+}
+
+fn match(self: *Cache, input: Request.Input, opts_: ?QueryOptions, exec: *const Execution) !js.Promise {
+    const opts = opts_ orelse QueryOptions{};
+    return matchIn(&.{self._bucket}, input, opts.ignoreSearch, exec);
+}
+
+pub fn matchIn(buckets: []const *Store.Bucket, input: Request.Input, ignore_search: bool, exec: *const Execution) !js.Promise {
+    const local = exec.js.local.?;
+    const key = try Key.init(input, exec);
+    if (key.method == .GET) {
+        for (buckets) |bucket| {
+            const entry = bucket.match(key.url, ignore_search) orelse continue;
+            const response = try toResponse(entry, exec);
+            response.acquireRef();
+            defer response.releaseRef(exec.page); // safely transfered to v8, release
+            return local.resolvePromise(response);
+        }
+    }
+    return local.resolvePromise({});
+}
+
+fn put(self: *Cache, input: Request.Input, response: *Response, exec: *const Execution) !js.Promise {
+    // Errors reject: the bridge turns an error from a promise-returning
+    // function into a rejection.
+    const local = exec.js.local.?;
+    const key = try Key.init(input, exec);
+    if (key.storable() == false) {
+        return local.typeError("Request must be an http(s) GET");
+    }
+    if (unstorable(response)) |reason| {
+        return local.typeError(reason);
+    }
+    const body = try response.consumeBytes(exec);
+
+    const allocator = self._origin.allocator;
+    const entry = try toEntry(allocator, key.url, response, body);
+    errdefer entry.deinit();
+
+    try self._bucket.put(allocator, entry);
+    return local.resolvePromise({});
+}
+
+fn delete(self: *Cache, input: Request.Input, opts_: ?QueryOptions, exec: *const Execution) !js.Promise {
+    const opts = opts_ orelse QueryOptions{};
+    const key = try Key.init(input, exec);
+    var deleted = false;
+    if (key.method == .GET) {
+        deleted = self._bucket.delete(key.url, opts.ignoreSearch);
+    }
+    return exec.js.local.?.resolvePromise(deleted);
+}
+
+fn keys(self: *Cache, exec: *const Execution) !js.Promise {
+    const entries = self._bucket.entries.values();
+
+    // call_arena: resolving runs microtasks, and a nested native call resets
+    // local_arena before the defer below gets to run.
+    var requests: std.ArrayList(*Request) = try .initCapacity(exec.call_arena, entries.len);
+    defer for (requests.items) |request| {
+        // once we know they've safely been transfered to v8, we can release them
+        request.releaseRef(exec.page);
+    };
+
+    for (entries) |entry| {
+        const url = try exec.call_arena.dupeZ(u8, entry.url);
+        const request = try Request.init(.{ .url = url }, null, exec);
+        request.acquireRef();
+        requests.appendAssumeCapacity(request);
+    }
+    return exec.js.local.?.resolvePromise(requests.items);
+}
+
+fn add(self: *Cache, input: Request.Input, exec: *const Execution) !js.Promise {
+    return self.addAll(&.{input}, exec);
+}
+
+fn addAll(self: *Cache, inputs: []const Request.Input, exec: *const Execution) !js.Promise {
+    const local = exec.js.local.?;
+
+    // call_arena: batch.release() below can settle the promise synchronously,
+    // and that runs microtasks (see keys).
+    const requests = try exec.call_arena.alloc(*Request, inputs.len);
+    var added_count: usize = 0;
+    defer for (requests[0..added_count]) |request| {
+        request.releaseRef(exec.page);
+    };
+
+    for (inputs, requests) |input, *request| {
+        request.* = try Request.init(input, null, exec);
+        request.*.acquireRef();
+        added_count += 1;
+
+        const key: Key = .{ .url = request.*._url, .method = request.*._method };
+        if (key.storable() == false) {
+            return local.typeError("Request must be an http(s) GET");
+        }
+    }
+
+    const resolver = local.createPromiseResolver();
+    const batch = try Batch.init(self, try resolver.persist(), requests, exec);
+    for (requests, batch.slots) |request, *slot| {
+        batch.pending += 1;
+        Fetch.start(request, .{ .ctx = slot, .callback = Batch.fetched }, exec) catch |err| {
+            log.warn(.http, "Cache.add fetch", .{ .err = err, .url = request._url });
+            batch.pending -= 1;
+            batch.outcome = .failed;
+            break;
+        };
+    }
+    batch.release();
+    return resolver.promise();
+}
+
+// An addAll in flight.
+const Batch = struct {
+    arena: *lp.Arena,
+    exec: *const Execution,
+    origin: *Store.Origin,
+    bucket: *Store.Bucket,
+    resolver: js.PromiseResolver.Global,
+    slots: []Slot,
+    staged: std.ArrayList(*Store.Entry),
+    outcome: enum { ok, failed, shutdown } = .ok,
+    pending: usize = 1,
+
+    const Slot = struct {
+        batch: *Batch,
+        url: []const u8,
+    };
+
+    fn init(cache: *const Cache, resolver: js.PromiseResolver.Global, requests: []const *Request, exec: *const Execution) !*Batch {
+        const arena = try exec.getArena(.small, "Cache.addAll");
+        errdefer arena.release();
+
+        const self = try arena.create(Batch);
+        self.* = .{
+            .arena = arena,
+            .exec = exec,
+            .origin = cache._origin,
+            .bucket = cache._bucket,
+            .resolver = resolver,
+            .slots = try arena.alloc(Slot, requests.len),
+            .staged = try .initCapacity(arena.allocator(), requests.len),
+        };
+        for (requests, self.slots) |request, *slot| {
+            slot.* = .{ .batch = self, .url = try arena.dupe(u8, request._url) };
+        }
+        return self;
+    }
+
+    // callback from Fetch on complete/error/shutdown
+    fn fetched(ctx: *anyopaque, result: Fetch.Completion.Result) void {
+        const slot: *Slot = @ptrCast(@alignCast(ctx));
+        const self = slot.batch;
+        defer self.release();
+
+        switch (result) {
+            .done => |response| if (self.outcome == .ok) {
+                self.stage(slot.url, response) catch {
+                    self.outcome = .failed;
+                };
+            },
+            .err => if (self.outcome == .ok) {
+                self.outcome = .failed;
+            },
+            .shutdown => self.outcome = .shutdown,
+        }
+    }
+
+    fn stage(self: *Batch, url: []const u8, response: *const Response) !void {
+        if (response._status < 200 or response._status > 299 or unstorable(response) != null) {
+            return error.Unstorable;
+        }
+        const entry = try toEntry(self.origin.allocator, url, response, response._body.bytes);
+        self.staged.appendAssumeCapacity(entry);
+    }
+
+    fn release(self: *Batch) void {
+        self.pending -= 1;
+        if (self.pending > 0) {
+            return;
+        }
+        defer self.arena.release();
+
+        if (self.outcome == .ok) {
+            self.commit() catch {
+                self.outcome = .failed;
+            };
+        }
+        for (self.staged.items) |entry| {
+            entry.deinit();
+        }
+
+        if (self.outcome == .shutdown) {
+            return;
+        }
+
+        var ls: js.Local.Scope = undefined;
+        self.exec.js.localScope(&ls);
+        defer ls.deinit();
+
+        const resolver = ls.toLocal(self.resolver);
+        switch (self.outcome) {
+            .ok => resolver.resolve("Cache.addAll", {}),
+            .failed => resolver.rejectError("Cache.addAll", .{ .type_error = "Request failed" }),
+            .shutdown => unreachable,
+        }
+    }
+
+    fn commit(self: *Batch) !void {
+        const allocator = self.origin.allocator;
+        try self.bucket.entries.ensureUnusedCapacity(allocator, self.staged.items.len);
+        for (self.staged.items) |entry| {
+            self.bucket.put(allocator, entry) catch unreachable;
+        }
+        self.staged.clearRetainingCapacity();
+    }
+};
+
+// What an entry is looked up by.
+const Key = struct {
+    url: [:0]const u8,
+    method: http.Method,
+
+    fn init(input: Request.Input, exec: *const Execution) !Key {
+        return switch (input) {
+            .request => |r| .{ .url = r._url, .method = r._method },
+            .url => |u| .{
+                .url = try URL.resolve(exec.call_arena, exec.base(), u, .{ .encoding = exec.charset.* }),
+                .method = .GET,
+            },
+        };
+    }
+
+    fn storable(self: Key) bool {
+        if (self.method != .GET) {
+            return false;
+        }
+        return std.mem.startsWith(u8, self.url, "http://") or std.mem.startsWith(u8, self.url, "https://");
+    }
+};
+
+// Why this response can't be stored, if it can't.
+fn unstorable(response: *const Response) ?[]const u8 {
+    if (response._status == 206) {
+        return "Partial response (status code 206) is unsupported";
+    }
+    if (response._body == .stream) {
+        return "Response with a ReadableStream body is unsupported";
+    }
+    for (response._headers._list._entries.items) |*header| {
+        if (std.ascii.eqlIgnoreCase(header.name.str(), "vary") == false) {
+            continue;
+        }
+        var it = std.mem.splitScalar(u8, header.value.str(), ',');
+        while (it.next()) |value| {
+            if (std.mem.eql(u8, std.mem.trim(u8, value, " \t"), "*")) {
+                return "Vary header contains *";
+            }
+        }
+    }
+    return null;
+}
+
+fn toEntry(allocator: Allocator, url: []const u8, response: *const Response, body: []const u8) !*Store.Entry {
+    const entry = try Store.Entry.create(allocator, url);
+    errdefer entry.deinit();
+
+    const arena = entry.arena.allocator();
+    const source = response._headers._list._entries.items;
+    const headers = try arena.alloc([2][]const u8, source.len);
+    for (source, headers) |*header, *kv| {
+        kv.* = .{ try arena.dupe(u8, header.name.str()), try arena.dupe(u8, header.value.str()) };
+    }
+
+    entry.response_url = try arena.dupeZ(u8, response._url);
+    entry.status = response._status;
+    entry.status_text = try arena.dupe(u8, response._status_text);
+    entry.response_type = response._type;
+    entry.is_redirected = response._is_redirected;
+    entry.headers = headers;
+    entry.body = try arena.dupe(u8, body);
+    return entry;
+}
+
+fn toResponse(entry: *const Store.Entry, exec: *const Execution) !*Response {
+    const arena = try exec.getPinnedArena(entry.body.len + entry.response_url.len + 256, "Cache.match");
+    errdefer arena.release();
+
+    const response = try arena.create(Response);
+    response.* = .{
+        ._arena = arena,
+        ._status = entry.status,
+        ._status_text = try arena.dupe(u8, entry.status_text),
+        ._url = try arena.dupeZ(u8, entry.response_url),
+        ._body = .{ .bytes = try arena.dupe(u8, entry.body) },
+        ._type = entry.response_type,
+        ._is_redirected = entry.is_redirected,
+        ._headers = try .initGuarded(.{ .strings = entry.headers }, .immutable, exec),
+    };
+    arena.report();
+    return response;
+}
+
+pub const JsApi = struct {
+    pub const bridge = js.Bridge(Cache);
+
+    pub const Meta = struct {
+        pub const name = "Cache";
+        pub const prototype_chain = bridge.prototypeChain();
+        pub var class_id: bridge.ClassId = undefined;
+    };
+
+    pub const match = bridge.function(Cache.match, .{});
+    pub const add = bridge.function(Cache.add, .{});
+    pub const addAll = bridge.function(Cache.addAll, .{});
+    pub const put = bridge.function(Cache.put, .{});
+    pub const delete = bridge.function(Cache.delete, .{});
+    pub const keys = bridge.function(Cache.keys, .{});
+};
diff --git a/src/browser/webapi/cache/CacheStorage.zig b/src/browser/webapi/cache/CacheStorage.zig
new file mode 100644
index 000000000..ba01f98ca
--- /dev/null
+++ b/src/browser/webapi/cache/CacheStorage.zig
@@ -0,0 +1,106 @@
+// Copyright (C) 2023-2025  Lightpanda (Selecy SAS)
+//
+// Francis Bouvier <francis@lightpanda.io>
+// Pierre Tachoire <pierre@lightpanda.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 <https://www.gnu.org/licenses/>.
+
+const js = @import("../../js/js.zig");
+
+const Request = @import("../net/Request.zig");
+
+const Cache = @import("Cache.zig");
+const Store = @import("Store.zig");
+
+const Execution = js.Execution;
+
+const CacheStorage = @This();
+
+_pad: bool = false,
+
+fn open(_: *CacheStorage, name: []const u8, exec: *const Execution) !js.Promise {
+    const origin = try storeOrigin(exec);
+    const bucket = try origin.open(name);
+    return exec.js.local.?.resolvePromise(try Cache.init(origin, bucket, exec));
+}
+
+fn has(_: *CacheStorage, name: []const u8, exec: *const Execution) !js.Promise {
+    const origin = try storeOrigin(exec);
+    return exec.js.local.?.resolvePromise(origin.find(name) != null);
+}
+
+fn delete(_: *CacheStorage, name: []const u8, exec: *const Execution) !js.Promise {
+    const origin = try storeOrigin(exec);
+    return exec.js.local.?.resolvePromise(try origin.delete(name));
+}
+
+fn keys(_: *CacheStorage, exec: *const Execution) !js.Promise {
+    const origin = try storeOrigin(exec);
+    return exec.js.local.?.resolvePromise(origin.buckets.keys());
+}
+
+const MatchOptions = struct {
+    cacheName: ?[]const u8 = null,
+    ignoreMethod: bool = false, // TODO
+    ignoreSearch: bool = false,
+    ignoreVary: bool = false, // TODO
+};
+
+fn match(_: *CacheStorage, input: Request.Input, opts_: ?MatchOptions, exec: *const Execution) !js.Promise {
+    const origin = try storeOrigin(exec);
+    const opts = opts_ orelse MatchOptions{};
+    if (opts.cacheName) |name| {
+        const bucket = origin.find(name) orelse return exec.js.local.?.resolvePromise({});
+        return Cache.matchIn(&.{bucket}, input, opts.ignoreSearch, exec);
+    }
+    return Cache.matchIn(origin.buckets.values(), input, opts.ignoreSearch, exec);
+}
+
+// Unavailable for an opaque origin, e.g. about:blank. The bridge turns the
+// error into a rejection.
+fn storeOrigin(exec: *const Execution) !*Store.Origin {
+    const origin = exec.origin() orelse return error.SecurityError;
+    return exec.session.cache_store.forOrigin(origin);
+}
+
+pub const JsApi = struct {
+    pub const bridge = js.Bridge(CacheStorage);
+
+    pub const Meta = struct {
+        pub const name = "CacheStorage";
+        pub const prototype_chain = bridge.prototypeChain();
+        pub var class_id: bridge.ClassId = undefined;
+        pub const empty_with_no_proto = true;
+    };
+
+    pub const open = bridge.function(CacheStorage.open, .{});
+    pub const has = bridge.function(CacheStorage.has, .{});
+    pub const delete = bridge.function(CacheStorage.delete, .{});
+    pub const keys = bridge.function(CacheStorage.keys, .{});
+    pub const match = bridge.function(CacheStorage.match, .{});
+};
+
+const testing = @import("../../../testing.zig");
+test "WebApi: CacheStorage" {
+    testing.silenceLog(&.{.http}); // addAll's 404 case
+    try testing.htmlRunner("cache/cache.html", .{ .experimental_features = .{ .serviceworker = true } });
+}
+
+test "WebApi: CacheStorage addAll torn down in flight" {
+    try testing.htmlRunner("cache/teardown.html", .{ .experimental_features = .{ .serviceworker = true } });
+}
+
+test "WebApi: CacheStorage disabled" {
+    try testing.htmlRunner("cache/disabled.html", .{});
+}
diff --git a/src/browser/webapi/cache/Store.zig b/src/browser/webapi/cache/Store.zig
new file mode 100644
index 000000000..64d519f9d
--- /dev/null
+++ b/src/browser/webapi/cache/Store.zig
@@ -0,0 +1,295 @@
+// Copyright (C) 2023-2026  Lightpanda (Selecy SAS)
+//
+// Francis Bouvier <francis@lightpanda.io>
+// Pierre Tachoire <pierre@lightpanda.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 <https://www.gnu.org/licenses/>.
+
+const std = @import("std");
+
+const URL = @import("../../URL.zig");
+const Response = @import("../net/Response.zig");
+
+const Allocator = std.mem.Allocator;
+
+// The Session's CacheStorage data: origin -> named caches -> entries. Plain
+// bytes only, no JS objects, so a Response stored by one realm can be served
+// to another. Memory only, for the life of the Session.
+const Store = @This();
+
+allocator: Allocator,
+// origin -> buckets -> url -> Entry
+origins: std.StringHashMapUnmanaged(*Origin) = .empty,
+
+pub fn init(allocator: Allocator) Store {
+    return .{ .allocator = allocator };
+}
+
+pub fn deinit(self: *Store) void {
+    const allocator = self.allocator;
+    var it = self.origins.iterator();
+    while (it.next()) |kv| {
+        const origin = kv.value_ptr.*;
+        for (origin.buckets.values()) |bucket| {
+            bucket.deinit(allocator);
+        }
+        for (origin.deleted.items) |bucket| {
+            bucket.deinit(allocator);
+        }
+        origin.buckets.deinit(allocator);
+        origin.deleted.deinit(allocator);
+        allocator.destroy(origin);
+        allocator.free(kv.key_ptr.*);
+    }
+    self.origins.deinit(allocator);
+}
+
+pub fn forOrigin(self: *Store, origin: []const u8) !*Origin {
+    const gop = try self.origins.getOrPut(self.allocator, origin);
+    if (gop.found_existing) {
+        return gop.value_ptr.*;
+    }
+    errdefer _ = self.origins.remove(origin);
+
+    const owned = try self.allocator.dupe(u8, origin);
+    errdefer self.allocator.free(owned);
+
+    const o = try self.allocator.create(Origin);
+    o.* = .{ .allocator = self.allocator };
+
+    gop.key_ptr.* = owned;
+    gop.value_ptr.* = o;
+    return o;
+}
+
+pub const Origin = struct {
+    allocator: Allocator,
+    buckets: std.StringArrayHashMapUnmanaged(*Bucket) = .empty,
+    // A Cache object outlives caches.delete, so we need to keep deleted buckets
+    deleted: std.ArrayList(*Bucket) = .empty,
+
+    pub fn find(self: *const Origin, name: []const u8) ?*Bucket {
+        return self.buckets.get(name);
+    }
+
+    pub fn open(self: *Origin, name: []const u8) !*Bucket {
+        if (self.find(name)) |bucket| {
+            return bucket;
+        }
+        const allocator = self.allocator;
+        try self.buckets.ensureUnusedCapacity(allocator, 1);
+
+        const owned = try allocator.dupe(u8, name);
+        errdefer allocator.free(owned);
+
+        const bucket = try allocator.create(Bucket);
+        bucket.* = .{ .name = owned };
+        self.buckets.putAssumeCapacity(owned, bucket);
+        return bucket;
+    }
+
+    pub fn delete(self: *Origin, name: []const u8) !bool {
+        const bucket = self.find(name) orelse return false;
+        try self.deleted.append(self.allocator, bucket);
+        _ = self.buckets.orderedRemove(name);
+        bucket.clear(self.allocator);
+        return true;
+    }
+};
+
+pub const Bucket = struct {
+    name: []const u8,
+    entries: std.StringArrayHashMapUnmanaged(*Entry) = .empty,
+
+    fn deinit(self: *Bucket, allocator: Allocator) void {
+        self.clear(allocator);
+        allocator.free(self.name);
+        allocator.destroy(self);
+    }
+
+    fn clear(self: *Bucket, allocator: Allocator) void {
+        for (self.entries.values()) |entry| {
+            entry.deinit();
+        }
+        self.entries.clearAndFree(allocator);
+    }
+
+    pub fn match(self: *const Bucket, url: []const u8, ignore_search: bool) ?*const Entry {
+        const idx = self.indexOf(url, ignore_search, 0) orelse return null;
+        return self.entries.values()[idx];
+    }
+
+    pub fn put(self: *Bucket, allocator: Allocator, entry: *Entry) !void {
+        try self.entries.ensureUnusedCapacity(allocator, 1);
+        // remove and add, so that it gets placed at the end
+        _ = self.delete(entry.url, false);
+        self.entries.putAssumeCapacity(entry.url, entry);
+    }
+
+    pub fn delete(self: *Bucket, url: []const u8, ignore_search: bool) bool {
+        if (ignore_search == false) {
+            const idx = self.indexOf(url, ignore_search, 0) orelse return false;
+            self.deleteAtIndex(idx);
+            return true;
+        }
+
+        // when we ignore_search, we can find multiple entries, e.g.:
+        // www.example.com/page.js?id=1
+        // www.example.com/page.js?id=2
+        var deleted = false;
+        var last_index: usize = 0;
+        while (self.indexOf(url, ignore_search, last_index)) |idx| {
+            self.deleteAtIndex(idx);
+            deleted = true;
+            last_index = idx;
+        }
+        return deleted;
+    }
+
+    fn deleteAtIndex(self: *Bucket, idx: usize) void {
+        const entry = self.entries.values()[idx];
+        self.entries.orderedRemoveAt(idx);
+        entry.deinit();
+    }
+
+    fn indexOf(self: *const Bucket, url: []const u8, ignore_search: bool, start: usize) ?usize {
+        if (ignore_search == false) {
+            return self.entries.getIndex(URL.stripFragment(url));
+        }
+        const needle = withoutSearch(url);
+        for (self.entries.values()[start..], start..) |entry, i| {
+            if (std.mem.eql(u8, entry.url_no_search, needle)) {
+                return i;
+            }
+        }
+        return null;
+    }
+};
+
+fn withoutSearch(url: []const u8) []const u8 {
+    return url[0 .. std.mem.indexOfAny(u8, url, "?#") orelse url.len];
+}
+
+// A stored request/response pair. Only the request's url is kept: entries are
+// always GET and Vary isn't considered.
+pub const Entry = struct {
+    arena: std.heap.ArenaAllocator,
+    status: u16,
+    status_text: []const u8,
+    is_redirected: bool,
+    url: []const u8, // without its fragment.
+    url_no_search: []const u8, // slices into url, for ignoreSearch.
+    response_url: [:0]const u8,
+    response_type: Response.Type,
+    headers: []const [2][]const u8,
+    body: []const u8,
+
+    pub fn create(allocator: Allocator, url: []const u8) !*Entry {
+        var arena = std.heap.ArenaAllocator.init(allocator);
+        errdefer arena.deinit();
+
+        const owned_url = try arena.allocator().dupe(u8, URL.stripFragment(url));
+        const self = try arena.allocator().create(Entry);
+        self.* = .{
+            .arena = arena,
+            .url = owned_url,
+            .url_no_search = withoutSearch(owned_url),
+            .response_url = "",
+            .status = 200,
+            .status_text = "",
+            .response_type = .default,
+            .is_redirected = false,
+            .headers = &.{},
+            .body = "",
+        };
+        return self;
+    }
+
+    pub fn deinit(self: *Entry) void {
+        self.arena.deinit();
+    }
+};
+
+const testing = @import("../../../testing.zig");
+test "Cache - Store: origins and buckets" {
+    var store = Store.init(testing.allocator);
+    defer store.deinit();
+
+    const a = try store.forOrigin("https://a.com");
+    try testing.expect(a == try store.forOrigin("https://a.com"));
+    try testing.expect(a != try store.forOrigin("https://b.com"));
+
+    const v1 = try a.open("v1");
+    try testing.expect(v1 == try a.open("v1"));
+    _ = try a.open("v2");
+    try testing.expectEqual(2, a.buckets.count());
+
+    try v1.put(a.allocator, try testEntry("https://a.com/x", "x"));
+    try testing.expectEqual(true, try a.delete("v1"));
+    try testing.expectEqual(false, try a.delete("v1"));
+    try testing.expectEqual(null, a.find("v1"));
+
+    // a deleted bucket stays usable
+    try testing.expectEqual(0, v1.entries.count());
+    try v1.put(a.allocator, try testEntry("https://a.com/x", "x"));
+}
+
+test "Cache - Store: put, match, delete" {
+    var store = Store.init(testing.allocator);
+    defer store.deinit();
+
+    const origin = try store.forOrigin("https://a.com");
+    const bucket = try origin.open("v1");
+
+    try bucket.put(origin.allocator, try testEntry("https://a.com/x?a=1", "one"));
+    try bucket.put(origin.allocator, try testEntry("https://a.com/x?a=2", "two"));
+    try bucket.put(origin.allocator, try testEntry("https://a.com/x?a=1", "three"));
+    try testing.expectEqual(2, bucket.entries.count());
+
+    try testing.expectEqual("three", bucket.match("https://a.com/x?a=1#frag", false).?.body);
+    try testing.expectEqual(null, bucket.match("https://a.com/x", false));
+    try testing.expectEqual("two", bucket.match("https://a.com/x", true).?.body);
+
+    try testing.expectEqual(false, bucket.delete("https://a.com/x", false));
+    try testing.expectEqual(true, bucket.delete("https://a.com/x?b=3", true));
+    try testing.expectEqual(0, bucket.entries.count());
+}
+
+test "Cache - Store: ignoreSearch delete removes every match" {
+    var store = Store.init(testing.allocator);
+    defer store.deinit();
+
+    const origin = try store.forOrigin("https://a.com");
+    const bucket = try origin.open("v1");
+
+    try bucket.put(origin.allocator, try testEntry("https://a.com/x?a=1", "1"));
+    try bucket.put(origin.allocator, try testEntry("https://a.com/x?a=2", "2"));
+    try bucket.put(origin.allocator, try testEntry("https://a.com/other", "3"));
+    try bucket.put(origin.allocator, try testEntry("https://a.com/x", "4"));
+    try bucket.put(origin.allocator, try testEntry("https://a.com/xy?a=1", "5"));
+    try bucket.put(origin.allocator, try testEntry("https://a.com/x?a=3#frag", "6"));
+
+    try testing.expectEqual(true, bucket.delete("https://a.com/x?b=1#f", true));
+    try testing.expectEqual(2, bucket.entries.count());
+    try testing.expectEqual("3", bucket.match("https://a.com/other", false).?.body);
+    try testing.expectEqual("5", bucket.match("https://a.com/xy", true).?.body);
+    try testing.expectEqual(false, bucket.delete("https://a.com/x", true));
+}
+
+fn testEntry(url: []const u8, body: []const u8) !*Entry {
+    const entry = try Entry.create(testing.allocator, url);
+    errdefer entry.deinit();
+    entry.body = try entry.arena.allocator().dupe(u8, body);
+    return entry;
+}
diff --git a/src/browser/webapi/net/Fetch.zig b/src/browser/webapi/net/Fetch.zig
index 14fab632d..aefc66c1d 100644
--- a/src/browser/webapi/net/Fetch.zig
+++ b/src/browser/webapi/net/Fetch.zig
@@ -41,15 +41,35 @@ _exec: *const Execution,
 _url: []const u8,
 _buf: std.ArrayList(u8),
 _response: *Response,
-_resolver: js.PromiseResolver.Global,
 _owns_response: bool,
 _signal: ?*AbortSignal,
 _manual_redirect: bool,
 _no_cors: bool,
+_sink: Sink,
 
 pub const Input = Request.Input;
 pub const InitOpts = Request.InitOpts;
 
+const Sink = union(enum) {
+    promise: js.PromiseResolver.Global,
+    completion: Completion,
+};
+
+// For a fetch made by Zig code (Cache.add), in place of fetch()'s promise.
+// Once `start` has returned without an error, `callback` fires exactly once.
+pub const Completion = struct {
+    ctx: *anyopaque,
+    callback: *const fn (ctx: *anyopaque, result: Result) void,
+
+    pub const Result = union(enum) {
+        // Only valid for the duration of the callback.
+        done: *Response,
+        err,
+        // The owner is being torn down: no JS.
+        shutdown,
+    };
+};
+
 pub fn init(input: Input, options: ?InitOpts, exec: *const Execution) !js.Promise {
     const resolver = exec.js.local.?.createPromiseResolver();
 
@@ -85,6 +105,16 @@ pub fn init(input: Input, options: ?InitOpts, exec: *const Execution) !js.Promis
         else => return err,
     };
 
+    try submit(request, body, .{ .promise = try resolver.persist() }, exec);
+    return resolver.promise();
+}
+
+pub fn start(request: *Request, completion: Completion, exec: *const Execution) !void {
+    const body = try request.bodyBytes();
+    return submit(request, body, .{ .completion = completion }, exec);
+}
+
+fn submit(request: *Request, body: ?[]const u8, sink: Sink, exec: *const Execution) !void {
     const response = try Response.initPending(exec);
     errdefer response.deinit(exec.page);
 
@@ -93,7 +123,7 @@ pub fn init(input: Input, options: ?InitOpts, exec: *const Execution) !js.Promis
         ._exec = exec,
         ._buf = .empty,
         ._url = try response._arena.dupe(u8, request._url),
-        ._resolver = try resolver.persist(),
+        ._sink = sink,
         ._response = response,
         ._owns_response = true,
         ._signal = request._signal,
@@ -105,7 +135,7 @@ pub fn init(input: Input, options: ?InitOpts, exec: *const Execution) !js.Promis
         log.debug(.http, "fetch", .{ .url = request._url });
     }
 
-    const transfer = exec.newRequest(.{
+    const transfer = try exec.newRequest(.{
         .ctx = fetch,
         .url = request._url,
         .method = request._method,
@@ -133,10 +163,7 @@ pub fn init(input: Input, options: ?InitOpts, exec: *const Execution) !js.Promis
         .done_callback = httpDoneCallback,
         .error_callback = httpErrorCallback,
         .shutdown_callback = httpShutdownCallback,
-    }) catch {
-        // OOM-class; nothing was committed and no callback fired.
-        return resolver.promise();
-    };
+    });
 
     {
         errdefer transfer.deinit();
@@ -172,7 +199,6 @@ pub fn init(input: Input, options: ?InitOpts, exec: *const Execution) !js.Promis
     // error from here would also fire the `errdefer response.deinit` above
     // and double-free the arena.
     transfer.submit() catch {};
-    return resolver.promise();
 }
 
 fn httpHeaderDoneCallback(transfer: *Transfer) !Transfer.HeaderResult {
@@ -284,6 +310,15 @@ fn httpDoneCallback(ctx: *anyopaque) !void {
         .len = self._buf.items.len,
     });
 
+    const resolver = switch (self._sink) {
+        .promise => |resolver| resolver,
+        .completion => |completion| {
+            self._owns_response = false;
+            defer response.deinit(self._exec.page);
+            return completion.callback(completion.ctx, .{ .done = response });
+        },
+    };
+
     var ls: js.Local.Scope = undefined;
     self._exec.js.localScope(&ls);
     defer ls.deinit();
@@ -291,7 +326,7 @@ fn httpDoneCallback(ctx: *anyopaque) !void {
     const js_val = try ls.local.zigValueToJs(self._response, .{});
     self._owns_response = false;
     response._arena.report();
-    return ls.toLocal(self._resolver).resolve("fetch done", js_val);
+    return ls.toLocal(resolver).resolve("fetch done", js_val);
 }
 
 fn httpErrorCallback(ctx: *anyopaque, err: anyerror) void {
@@ -320,23 +355,33 @@ fn httpErrorCallback(ctx: *anyopaque, err: anyerror) void {
         response.deinit(self._exec.page);
     };
 
+    const resolver = switch (self._sink) {
+        .promise => |resolver| resolver,
+        .completion => |completion| return completion.callback(completion.ctx, .err),
+    };
+
     var ls: js.Local.Scope = undefined;
     self._exec.js.localScope(&ls);
     defer ls.deinit();
 
     // fetch() must reject with a TypeError on network errors per spec
-    ls.toLocal(self._resolver).rejectError("fetch error", .{ .type_error = "fetch error" });
+    ls.toLocal(resolver).rejectError("fetch error", .{ .type_error = "fetch error" });
 }
 
 fn httpShutdownCallback(ctx: *anyopaque) void {
     const self: *Fetch = @ptrCast(@alignCast(ctx));
 
     if (self._owns_response) {
+        const sink = self._sink;
         var response = self._response;
         response._http_transfer = null;
         response.deinit(self._exec.page);
         // Do not access `self` after this point: the Fetch struct was
         // allocated from response._arena which has been released.
+        switch (sink) {
+            .promise => {},
+            .completion => |completion| completion.callback(completion.ctx, .shutdown),
+        }
     }
 }
 
diff --git a/src/browser/webapi/net/Response.zig b/src/browser/webapi/net/Response.zig
index 9cc1a0202..de209e081 100644
--- a/src/browser/webapi/net/Response.zig
+++ b/src/browser/webapi/net/Response.zig
@@ -338,6 +338,15 @@ fn consume(self: *Response, exec: *const Execution) !void {
     }
 }
 
+pub fn consumeBytes(self: *Response, exec: *const Execution) ![]const u8 {
+    try self.consume(exec);
+    return switch (self._body) {
+        .empty => "",
+        .bytes => |b| b,
+        .stream => exec.js.local.?.typeError("Response with a ReadableStream body is unsupported"),
+    };
+}
+
 pub fn getText(self: *Response, exec: *const Execution) !js.Promise {
     return self.consumeAs(.text, exec);
 }