diff --git a/web/src/components/CitationPanel.vue b/web/src/components/CitationPanel.vue
new file mode 100644
index 0000000..b0a8fb8
--- /dev/null
+++ b/web/src/components/CitationPanel.vue
@@ -0,0 +1,69 @@
+<template>
+  <div class="citation-panel">
+    <button
+      class="citation-toggle"
+      :aria-expanded="open"
+      @click="open = !open"
+    >
+      <span class="citation-badge" :class="{ 'nat20': showNat20 }" aria-hidden="true">
+        {{ showNat20 ? "⚀ Natural 20" : `p.${citation.page_number}` }}
+      </span>
+      <span class="citation-doc">{{ docTitle }}</span>
+      <span class="citation-chevron">{{ open ? "▲" : "▼" }}</span>
+    </button>
+
+    <div class="citation-body" v-show="open" role="region" :aria-label="`Excerpt from page ${citation.page_number}`">
+      <p class="citation-source-label">Source text (not paraphrased):</p>
+      <blockquote class="citation-text">{{ citation.snippet }}</blockquote>
+    </div>
+  </div>
+</template>
+
+<script setup lang="ts">
+import { onMounted, ref } from "vue"
+import type { Citation } from "@/api"
+
+const props = defineProps<{
+    citation: Citation
+    docTitle?: string
+    bm25Score?: number
+}>()
+
+const open = ref(false)
+const showNat20 = ref(false)
+
+const NAT20_THRESHOLD = 8.0
+
+onMounted(() => {
+    const prefersReduced = window.matchMedia("(prefers-reduced-motion: reduce)").matches
+    if (!prefersReduced && props.bm25Score && props.bm25Score >= NAT20_THRESHOLD) {
+        showNat20.value = true
+        setTimeout(() => { showNat20.value = false }, 300)
+    }
+})
+</script>
+
+<style scoped>
+.citation-panel { border: 1px solid var(--color-border); border-radius: var(--radius-sm); margin-bottom: 0.5rem; overflow: hidden; }
+.citation-toggle {
+    width: 100%; display: flex; align-items: center; gap: 0.75rem; padding: 0.6rem 0.75rem;
+    background: var(--color-surface-alt); border: none; cursor: pointer; color: var(--color-text);
+    text-align: left;
+}
+.citation-toggle:hover { background: var(--color-border); }
+.citation-badge {
+    font-size: 0.75rem; font-weight: 700; padding: 2px 8px;
+    background: var(--color-surface); border-radius: var(--radius-sm);
+    border: 1px solid var(--color-border); font-family: var(--font-mono);
+    white-space: nowrap; transition: background var(--transition-fast), color var(--transition-fast);
+}
+.citation-badge.nat20 { background: var(--color-accent); color: #fff; border-color: var(--color-accent); }
+.citation-doc { flex: 1; font-size: 0.85rem; color: var(--color-text-muted); }
+.citation-chevron { font-size: 0.7rem; color: var(--color-text-muted); }
+.citation-body { padding: 0.75rem; background: var(--color-surface); }
+.citation-source-label { font-size: 0.75rem; color: var(--color-text-muted); margin-bottom: 0.4rem; font-style: italic; }
+.citation-text {
+    border-left: 3px solid var(--color-accent); padding-left: 0.75rem;
+    font-size: 0.9rem; color: var(--color-text); line-height: 1.6;
+}
+</style>
diff --git a/web/src/views/ChatView.vue b/web/src/views/ChatView.vue
index 2430e3b..c5cb448 100644
--- a/web/src/views/ChatView.vue
+++ b/web/src/views/ChatView.vue
@@ -1,2 +1,239 @@
-<template><div>Chat coming soon.</div></template>
-<script setup lang="ts"></script>
+<template>
+  <div class="chat-layout">
+    <!-- Message pane -->
+    <div class="chat-pane">
+      <div class="chat-messages" ref="messagesEl">
+        <p class="empty-chat" v-if="history.length === 0">
+          Ask a question across your indexed rulebooks.
+          No rulebooks indexed? Go to <RouterLink to="/">Library</RouterLink> first.
+        </p>
+
+        <div
+          v-for="(msg, i) in history"
+          :key="i"
+          class="message"
+          :class="msg.role"
+        >
+          <div class="message-body">{{ msg.content }}</div>
+          <div class="message-citations" v-if="msg.citations?.length">
+            <p class="citations-label">Sources:</p>
+            <CitationPanel
+              v-for="(cite, j) in msg.citations"
+              :key="j"
+              :citation="cite"
+              :doc-title="docTitles[cite.doc_id] ?? cite.doc_id"
+            />
+          </div>
+        </div>
+
+        <div class="message assistant loading" v-if="thinking">
+          <div class="loading-dots"><span /><span /><span /></div>
+        </div>
+      </div>
+
+      <p class="error-banner" v-if="errorMsg" role="alert">
+        {{ errorMsg }}
+        <span v-if="error402"> — <RouterLink to="/">Library</RouterLink> or set PAGEPIPER_OLLAMA_URL.</span>
+      </p>
+
+      <form class="chat-input-row" @submit.prevent="send">
+        <input
+          ref="inputEl"
+          v-model="draft"
+          class="chat-input"
+          placeholder="Ask about your rulebooks…"
+          :disabled="thinking"
+          aria-label="Chat message"
+          autofocus
+        />
+        <button class="btn-send" type="submit" :disabled="thinking || !draft.trim()">Send</button>
+      </form>
+    </div>
+
+    <!-- Book filter sidebar -->
+    <aside class="sidebar" role="complementary" aria-label="Filter by book">
+      <h2 class="sidebar-title">Books</h2>
+      <p class="sidebar-hint">Select books to search (all = none selected)</p>
+      <label
+        v-for="doc in readyDocs"
+        :key="doc.id"
+        class="book-filter"
+      >
+        <input type="checkbox" :value="doc.id" v-model="selectedDocs" />
+        {{ doc.title }}
+      </label>
+    </aside>
+  </div>
+</template>
+
+<script setup lang="ts">
+import { computed, nextTick, onMounted, ref } from "vue"
+import { RouterLink } from "vue-router"
+import { api, type Citation, type Document } from "@/api"
+import CitationPanel from "@/components/CitationPanel.vue"
+
+interface ChatMessage {
+    role: "user" | "assistant"
+    content: string
+    citations?: Citation[]
+}
+
+const history = ref<ChatMessage[]>([])
+const draft = ref("")
+const thinking = ref(false)
+const errorMsg = ref("")
+const error402 = ref(false)
+const messagesEl = ref<HTMLElement | null>(null)
+const inputEl = ref<HTMLInputElement | null>(null)
+const allDocs = ref<Document[]>([])
+const selectedDocs = ref<string[]>([])
+
+const readyDocs = computed(() => allDocs.value.filter(d => d.status === "ready"))
+const docTitles = computed(() =>
+    Object.fromEntries(allDocs.value.map(d => [d.id, d.title]))
+)
+
+onMounted(async () => {
+    allDocs.value = await api.getLibrary().catch(() => [])
+    inputEl.value?.focus()
+})
+
+async function send() {
+    const msg = draft.value.trim()
+    if (!msg || thinking.value) return
+
+    draft.value = ""
+    errorMsg.value = ""
+    error402.value = false
+    history.value.push({ role: "user", content: msg })
+    thinking.value = true
+    await nextTick()
+    scrollBottom()
+
+    try {
+        const docIds = selectedDocs.value.length ? selectedDocs.value : undefined
+        const apiHistory = history.value.slice(0, -1).map(m => ({ role: m.role, content: m.content }))
+        const result = await api.chat(msg, apiHistory, docIds)
+        history.value.push({ role: "assistant", content: result.answer, citations: result.citations })
+    } catch (err: unknown) {
+        const e = err as Error & { status?: number; detail?: { message?: string } }
+        if (e.status === 402) {
+            error402.value = true
+            errorMsg.value = e.detail?.message ?? "Ollama not configured. Set PAGEPIPER_OLLAMA_URL."
+        } else {
+            errorMsg.value = e.message ?? "Something went wrong."
+        }
+    } finally {
+        thinking.value = false
+        await nextTick()
+        scrollBottom()
+        inputEl.value?.focus()
+    }
+}
+
+function scrollBottom() {
+    if (messagesEl.value) {
+        messagesEl.value.scrollTop = messagesEl.value.scrollHeight
+    }
+}
+</script>
+
+<style scoped>
+.chat-layout {
+    display: flex;
+    height: calc(100vh - 56px);
+    overflow: hidden;
+}
+
+.chat-pane {
+    flex: 1;
+    display: flex;
+    flex-direction: column;
+    overflow: hidden;
+}
+
+.chat-messages {
+    flex: 1;
+    overflow-y: auto;
+    padding: 1.5rem;
+    display: flex;
+    flex-direction: column;
+    gap: 1rem;
+}
+
+.empty-chat { color: var(--color-text-muted); line-height: 1.8; }
+
+.message { max-width: 80%; }
+.message.user { align-self: flex-end; }
+.message.assistant { align-self: flex-start; }
+
+.message-body {
+    background: var(--color-surface);
+    border: 1px solid var(--color-border);
+    border-radius: var(--radius-md);
+    padding: 0.75rem 1rem;
+    line-height: 1.6;
+    white-space: pre-wrap;
+}
+.message.user .message-body {
+    background: var(--color-surface-alt);
+    border-color: transparent;
+}
+
+.message-citations { margin-top: 0.75rem; }
+.citations-label { font-size: 0.75rem; color: var(--color-text-muted); margin-bottom: 0.4rem; font-style: italic; }
+
+.loading-dots { display: flex; gap: 6px; padding: 0.75rem 1rem; }
+.loading-dots span {
+    width: 8px; height: 8px; border-radius: 50%;
+    background: var(--color-text-muted);
+    animation: bounce 1.2s ease-in-out infinite;
+}
+.loading-dots span:nth-child(2) { animation-delay: 0.2s; }
+.loading-dots span:nth-child(3) { animation-delay: 0.4s; }
+@keyframes bounce { 0%, 80%, 100% { transform: scale(0.6); } 40% { transform: scale(1); } }
+@media (prefers-reduced-motion: reduce) { .loading-dots span { animation: none; opacity: 0.5; } }
+
+.error-banner {
+    padding: 0.75rem 1.5rem;
+    background: color-mix(in srgb, var(--color-error) 15%, var(--color-surface));
+    color: var(--color-error);
+    font-size: 0.9rem;
+}
+
+.chat-input-row {
+    display: flex;
+    gap: 0.5rem;
+    padding: 1rem 1.5rem;
+    border-top: 1px solid var(--color-border);
+    background: var(--color-surface);
+}
+.chat-input {
+    flex: 1; padding: 0.6rem 1rem;
+    background: var(--color-bg); border: 1px solid var(--color-border);
+    border-radius: var(--radius-sm); color: var(--color-text); font-size: 1rem;
+}
+.chat-input:focus { outline: 2px solid var(--color-accent); border-color: transparent; }
+.btn-send {
+    padding: 0.6rem 1.25rem; background: var(--color-accent); color: #fff;
+    border: none; border-radius: var(--radius-sm); cursor: pointer; font-size: 0.95rem;
+}
+.btn-send:disabled { opacity: 0.4; cursor: default; }
+
+.sidebar {
+    width: 240px; border-left: 1px solid var(--color-border);
+    background: var(--color-surface); overflow-y: auto; padding: 1rem;
+}
+.sidebar-title { font-size: 1rem; font-weight: 600; margin-bottom: 0.5rem; }
+.sidebar-hint { font-size: 0.75rem; color: var(--color-text-muted); margin-bottom: 0.75rem; line-height: 1.4; }
+.book-filter {
+    display: flex; align-items: flex-start; gap: 0.5rem;
+    font-size: 0.85rem; margin-bottom: 0.5rem; cursor: pointer; line-height: 1.4;
+}
+
+@media (max-width: 640px) {
+    .chat-layout { flex-direction: column-reverse; }
+    .sidebar { width: 100%; height: auto; max-height: 30vh; border-left: none; border-top: 1px solid var(--color-border); }
+    .message { max-width: 95%; }
+}
+</style>