diff --git a/web/README.md b/web/README.md
index 5bfef98..f70945e 100644
--- a/web/README.md
+++ b/web/README.md
@@ -58,6 +58,15 @@ it also works as a project switcher from anywhere. `<RouterView
 :key="route.path">` remounts the view on every path change so switching
 projects always does a fresh load.
 
+Below `768px` (`style.css`'s one layout breakpoint) the sidebar becomes an
+off-canvas drawer instead of sitting beside the page: `position: fixed`,
+translated out of view by default, slid in via a `.sidebar--open` class.
+`App.vue` owns the `drawerOpen` state -- a `☰` button in the header (hidden
+above the breakpoint) opens it; a backdrop tap, the drawer's own `✕` (which
+`AppSidebar` emits `close` for), or any navigation (a `route.fullPath`
+watcher) closes it. Above the breakpoint `drawerOpen` just goes unused, since
+nothing renders the button that would set it.
+
 `/` redirects to `/dashboard` (`DashboardView.vue`): a full-width grid linking
 to each project (title + card count), with a **"Create a project" tile**
 styled to match sitting last in the same grid (creating one stays on the
diff --git a/web/src/App.vue b/web/src/App.vue
index 5322d62..10dda13 100644
--- a/web/src/App.vue
+++ b/web/src/App.vue
@@ -1,5 +1,5 @@
 <script setup lang="ts">
-import { computed } from 'vue'
+import { computed, ref, watch } from 'vue'
 import { RouterLink, RouterView, useRoute, useRouter } from 'vue-router'
 import AppSidebar from './components/AppSidebar.vue'
 import PasskeyNotice from './components/PasskeyNotice.vue'
@@ -19,6 +19,14 @@ const route = useRoute()
 // profile) and stays mounted as you navigate between them.
 const showSidebar = computed(() => auth.isAuthenticated && route.meta.requiresAuth === true)
 
+// On narrow viewports the sidebar becomes an off-canvas drawer (see
+// .sidebar's mobile rules in style.css), opened via the header's "menu"
+// button; on wide viewports drawerOpen is never set, so it's inert (the
+// button that sets it is itself hidden there). Close it on every navigation
+// so it doesn't stay open over the page it was just used to get to.
+const drawerOpen = ref(false)
+watch(() => route.fullPath, () => (drawerOpen.value = false))
+
 async function onLogout() {
   auth.logout()
   projects.reset()
@@ -31,7 +39,20 @@ async function onLogout() {
 <template>
   <div class="app">
     <header class="app__bar">
-      <span class="app__brand">Projects</span>
+      <div class="app__bar-left">
+        <button
+          v-if="showSidebar"
+          type="button"
+          class="app__menu-toggle"
+          aria-label="Open menu"
+          aria-haspopup="true"
+          :aria-expanded="drawerOpen"
+          @click="drawerOpen = true"
+        >
+          &#9776;
+        </button>
+        <span class="app__brand">Projects</span>
+      </div>
 
       <div v-if="auth.isAuthenticated" class="app__account">
         <RouterLink to="/profile" class="app__email">{{ auth.user?.email }}</RouterLink>
@@ -42,7 +63,11 @@ async function onLogout() {
     <PasskeyNotice />
 
     <div class="app__body">
-      <AppSidebar v-if="showSidebar" />
+      <!-- Mobile only (see style.css): dims the page and closes the drawer
+           on tap, while the sidebar is a fixed off-canvas panel over it. -->
+      <div v-if="showSidebar && drawerOpen" class="app__drawer-backdrop" @click="drawerOpen = false" />
+
+      <AppSidebar v-if="showSidebar" :class="{ 'sidebar--open': drawerOpen }" @close="drawerOpen = false" />
 
       <main class="app__main" :class="{ 'app__main--wide': route.meta.wide }">
         <!-- Key by path so navigating between projects via the sidebar remounts
diff --git a/web/src/components/AppSidebar.vue b/web/src/components/AppSidebar.vue
index 721acce..7aa72a9 100644
--- a/web/src/components/AppSidebar.vue
+++ b/web/src/components/AppSidebar.vue
@@ -16,6 +16,11 @@ const inbox = useInboxStore()
 const router = useRouter()
 const route = useRoute()
 
+// Only meaningful on mobile, where the sidebar is a drawer (see style.css) --
+// its own close button emits this to tell App.vue to close it (App.vue also
+// closes it directly on a backdrop tap or any navigation).
+const emit = defineEmits<{ close: [] }>()
+
 const loadError = ref<string | null>(null)
 
 onMounted(() => {
@@ -96,6 +101,8 @@ async function onInboxChange(change: ColumnChange) {
 
 <template>
   <aside class="sidebar">
+    <button type="button" class="sidebar__close" aria-label="Close menu" @click="emit('close')">&#10005;</button>
+
     <nav class="sidebar__nav">
       <RouterLink :to="{ name: 'dashboard' }" class="sidebar__link" active-class="sidebar__link--active">
         <svg class="sidebar__icon" viewBox="0 0 16 16" aria-hidden="true">
diff --git a/web/src/style.css b/web/src/style.css
index 0486333..c6e84c2 100644
--- a/web/src/style.css
+++ b/web/src/style.css
@@ -62,10 +62,36 @@ body {
   border-bottom: 1px solid var(--border);
 }
 
+.app__bar-left {
+  display: flex;
+  align-items: center;
+  gap: 0.75rem;
+  min-width: 0;
+}
+
 .app__brand {
   font-weight: 600;
 }
 
+/* Opens the sidebar drawer on mobile (see the sidebar's own mobile rules
+   below) -- hidden here, shown only under that same breakpoint. */
+.app__menu-toggle {
+  display: none;
+  flex: none;
+  border: 1px solid var(--border);
+  background: var(--bg);
+  color: var(--text);
+  border-radius: 8px;
+  padding: 0.35rem 0.55rem;
+  font-size: 1rem;
+  line-height: 1;
+  cursor: pointer;
+}
+
+.app__menu-toggle:hover {
+  border-color: var(--muted);
+}
+
 .app__account {
   display: flex;
   align-items: center;
@@ -118,6 +144,70 @@ body {
   background: var(--surface);
 }
 
+/* Only shown once .sidebar becomes a drawer, under the mobile breakpoint
+   below -- hidden here. */
+.sidebar__close {
+  display: none;
+  position: absolute;
+  top: 0.75rem;
+  right: 0.75rem;
+  border: none;
+  background: none;
+  color: var(--muted);
+  cursor: pointer;
+  font-size: 1rem;
+  padding: 0.3rem 0.5rem;
+  border-radius: 6px;
+}
+
+.sidebar__close:hover {
+  background: var(--bg);
+  color: var(--text);
+}
+
+/* --- mobile: sidebar becomes an off-canvas drawer ---------------------- */
+
+@media (max-width: 768px) {
+  .app__menu-toggle {
+    display: inline-flex;
+  }
+
+  .app__body {
+    padding: 1rem;
+  }
+
+  .sidebar {
+    position: fixed;
+    top: 0;
+    left: 0;
+    z-index: 200;
+    width: 85vw;
+    max-width: 20rem;
+    height: 100vh;
+    border: none;
+    border-radius: 0;
+    border-right: 1px solid var(--border);
+    padding-top: 2.75rem;
+    transform: translateX(-100%);
+    transition: transform 0.2s ease;
+  }
+
+  .sidebar--open {
+    transform: translateX(0);
+  }
+
+  .sidebar__close {
+    display: block;
+  }
+
+  .app__drawer-backdrop {
+    position: fixed;
+    inset: 0;
+    z-index: 150;
+    background: rgba(0, 0, 0, 0.45);
+  }
+}
+
 .sidebar__nav {
   display: flex;
   flex-direction: column;