diff --git a/app/backend/main.py b/app/backend/main.py
index 4b3724e5..3ce50f43 100644
--- a/app/backend/main.py
+++ b/app/backend/main.py
@@ -83,6 +83,7 @@ async def stream_chat(request: Request) -> Response:
     # Restore session state from incoming AG-UI state (look under namespaced key)
     initial_qa_history: list[QAResponse] = []
     session_id: str | None = None
+    document_filter: list[str] = []
     state = getattr(run_input, "state", None)
     if state:
         chat_state = state.get(AGUI_STATE_KEY, state)
@@ -91,6 +92,7 @@ async def stream_chat(request: Request) -> Response:
                 QAResponse(**qa) for qa in chat_state.get("qa_history", [])
             ]
         session_id = chat_state.get("session_id")
+        document_filter = chat_state.get("document_filter", [])
 
     # Determine session_id: prefer state, fall back to thread_id, generate UUID if neither
     thread_id = getattr(run_input, "thread_id", None)
@@ -103,6 +105,7 @@ async def stream_chat(request: Request) -> Response:
         session_state=ChatSessionState(
             session_id=session_id,
             qa_history=initial_qa_history,
+            document_filter=document_filter,
         ),
         state_key=AGUI_STATE_KEY,
     )
diff --git a/app/frontend/app/api/documents/route.ts b/app/frontend/app/api/documents/route.ts
new file mode 100644
index 00000000..0f41863f
--- /dev/null
+++ b/app/frontend/app/api/documents/route.ts
@@ -0,0 +1,16 @@
+import { NextResponse } from "next/server";
+
+export async function GET() {
+	const backendUrl = process.env.BACKEND_URL || "http://backend:8000";
+
+	try {
+		const response = await fetch(`${backendUrl}/api/documents`);
+		const data = await response.json();
+		return NextResponse.json(data);
+	} catch {
+		return NextResponse.json(
+			{ documents: [], error: "Backend unavailable" },
+			{ status: 503 },
+		);
+	}
+}
diff --git a/app/frontend/components/Chat.tsx b/app/frontend/components/Chat.tsx
index 247ce0f5..da553fe4 100644
--- a/app/frontend/components/Chat.tsx
+++ b/app/frontend/components/Chat.tsx
@@ -12,6 +12,7 @@ import "@copilotkit/react-ui/styles.css";
 import CitationBlock from "./CitationBlock";
 import ContextPanel from "./ContextPanel";
 import DbInfo from "./DbInfo";
+import DocumentFilter from "./DocumentFilter";
 
 // Must match AGUI_STATE_KEY from haiku.rag.agents.chat
 const AGUI_STATE_KEY = "haiku.rag.chat";
@@ -44,6 +45,7 @@ interface ChatSessionState {
 	citations: Citation[];
 	qa_history: QAResponse[];
 	session_context: SessionContext | null;
+	document_filter: string[];
 }
 
 // AG-UI state is namespaced under AGUI_STATE_KEY
@@ -369,23 +371,59 @@ function ToolCallIndicator({
 	);
 }
 
+function FilterIcon() {
+	return (
+		<svg
+			width="18"
+			height="18"
+			viewBox="0 0 24 24"
+			fill="none"
+			stroke="currentColor"
+			strokeWidth="2"
+			strokeLinecap="round"
+			strokeLinejoin="round"
+		>
+			<polygon points="22 3 2 3 10 12.46 10 19 14 21 14 12.46 22 3" />
+		</svg>
+	);
+}
+
 function ChatContentInner() {
 	const [contextOpen, setContextOpen] = useState(false);
+	const [filterOpen, setFilterOpen] = useState(false);
 
-	const { state: agentState } = useCoAgent<AgentState>({
-		name: "chat_agent",
-		initialState: {
-			[AGUI_STATE_KEY]: {
-				session_id: "",
-				citations: [],
-				qa_history: [],
-				session_context: null,
+	const { state: agentState, setState: setAgentState } = useCoAgent<AgentState>(
+		{
+			name: "chat_agent",
+			initialState: {
+				[AGUI_STATE_KEY]: {
+					session_id: "",
+					citations: [],
+					qa_history: [],
+					session_context: null,
+					document_filter: [],
+				},
 			},
 		},
-	});
+	);
 
-	// Extract session context from agent state
+	// Extract session context and document filter from agent state
 	const sessionContext = agentState?.[AGUI_STATE_KEY]?.session_context ?? null;
+	const documentFilter = agentState?.[AGUI_STATE_KEY]?.document_filter ?? [];
+
+	const handleFilterApply = (selected: string[]) => {
+		setAgentState({
+			...agentState,
+			[AGUI_STATE_KEY]: {
+				...agentState?.[AGUI_STATE_KEY],
+				session_id: agentState?.[AGUI_STATE_KEY]?.session_id ?? "",
+				citations: agentState?.[AGUI_STATE_KEY]?.citations ?? [],
+				qa_history: agentState?.[AGUI_STATE_KEY]?.qa_history ?? [],
+				session_context: agentState?.[AGUI_STATE_KEY]?.session_context ?? null,
+				document_filter: selected,
+			},
+		});
+	};
 
 	useCoAgentStateRender<AgentState>({
 		name: "chat_agent",
@@ -513,6 +551,21 @@ function ChatContentInner() {
 			<div className="chat-wrapper">
 				<div className="chat-container">
 					<div className="chat-header">
+						<button
+							type="button"
+							className={`header-btn ${documentFilter.length > 0 ? "has-content" : ""}`}
+							onClick={() => setFilterOpen(true)}
+							title={
+								documentFilter.length > 0
+									? `Filtering: ${documentFilter.length} document(s)`
+									: "Filter documents"
+							}
+						>
+							<FilterIcon />
+							{documentFilter.length > 0
+								? `Filter (${documentFilter.length})`
+								: "Filter"}
+						</button>
 						<button
 							type="button"
 							className={`header-btn ${sessionContext?.summary ? "has-content" : ""}`}
@@ -544,6 +597,12 @@ function ChatContentInner() {
 				onClose={() => setContextOpen(false)}
 				sessionContext={sessionContext}
 			/>
+			<DocumentFilter
+				isOpen={filterOpen}
+				onClose={() => setFilterOpen(false)}
+				selected={documentFilter}
+				onApply={handleFilterApply}
+			/>
 		</>
 	);
 }
diff --git a/app/frontend/components/DocumentFilter.tsx b/app/frontend/components/DocumentFilter.tsx
new file mode 100644
index 00000000..27caffd8
--- /dev/null
+++ b/app/frontend/components/DocumentFilter.tsx
@@ -0,0 +1,381 @@
+"use client";
+
+import { useCallback, useEffect, useId, useState } from "react";
+
+interface Document {
+	id: string;
+	title: string | null;
+	uri: string | null;
+}
+
+interface DocumentFilterProps {
+	isOpen: boolean;
+	onClose: () => void;
+	selected: string[];
+	onApply: (selected: string[]) => void;
+}
+
+function FilterIcon() {
+	return (
+		<svg
+			width="24"
+			height="24"
+			viewBox="0 0 24 24"
+			fill="none"
+			stroke="currentColor"
+			strokeWidth="1.5"
+			strokeLinecap="round"
+			strokeLinejoin="round"
+		>
+			<polygon points="22 3 2 3 10 12.46 10 19 14 21 14 12.46 22 3" />
+		</svg>
+	);
+}
+
+export default function DocumentFilter({
+	isOpen,
+	onClose,
+	selected,
+	onApply,
+}: DocumentFilterProps) {
+	const titleId = useId();
+	const [documents, setDocuments] = useState<Document[]>([]);
+	const [loading, setLoading] = useState(true);
+	const [searchTerm, setSearchTerm] = useState("");
+	const [localSelected, setLocalSelected] = useState<Set<string>>(
+		new Set(selected),
+	);
+
+	// Reset local state when modal opens
+	useEffect(() => {
+		if (isOpen) {
+			setLocalSelected(new Set(selected));
+			setSearchTerm("");
+		}
+	}, [isOpen, selected]);
+
+	// Fetch documents when modal opens
+	useEffect(() => {
+		if (isOpen && documents.length === 0) {
+			setLoading(true);
+			fetch("/api/documents")
+				.then((res) => res.json())
+				.then((data) => {
+					setDocuments(data.documents || []);
+					setLoading(false);
+				})
+				.catch(() => {
+					setLoading(false);
+				});
+		}
+	}, [isOpen, documents.length]);
+
+	const handleKeyDown = useCallback(
+		(e: React.KeyboardEvent) => {
+			if (e.key === "Escape") {
+				onClose();
+			}
+		},
+		[onClose],
+	);
+
+	const toggleDocument = (displayName: string) => {
+		setLocalSelected((prev) => {
+			const next = new Set(prev);
+			if (next.has(displayName)) {
+				next.delete(displayName);
+			} else {
+				next.add(displayName);
+			}
+			return next;
+		});
+	};
+
+	const handleApply = () => {
+		onApply(Array.from(localSelected));
+		onClose();
+	};
+
+	const handleClearAll = () => {
+		setLocalSelected(new Set());
+	};
+
+	const getDisplayName = (doc: Document) => doc.title || doc.uri || doc.id;
+
+	const filteredDocuments = documents.filter((doc) => {
+		if (!searchTerm) return true;
+		const displayName = getDisplayName(doc).toLowerCase();
+		return displayName.includes(searchTerm.toLowerCase());
+	});
+
+	if (!isOpen) {
+		return null;
+	}
+
+	return (
+		<>
+			<style>{`
+				.filter-modal-overlay {
+					position: fixed;
+					top: 0;
+					left: 0;
+					right: 0;
+					bottom: 0;
+					background: rgba(0, 0, 0, 0.5);
+					display: flex;
+					align-items: center;
+					justify-content: center;
+					z-index: 1000;
+				}
+				.filter-modal {
+					background: white;
+					border-radius: 12px;
+					padding: 1.5rem;
+					width: 90%;
+					max-width: 500px;
+					max-height: 80vh;
+					display: flex;
+					flex-direction: column;
+					position: relative;
+					box-shadow: 0 20px 25px -5px rgba(0, 0, 0, 0.1), 0 10px 10px -5px rgba(0, 0, 0, 0.04);
+				}
+				.filter-modal-header {
+					display: flex;
+					align-items: center;
+					gap: 0.75rem;
+					margin-bottom: 0.5rem;
+				}
+				.filter-modal-icon {
+					display: flex;
+					align-items: center;
+					justify-content: center;
+					width: 40px;
+					height: 40px;
+					border-radius: 10px;
+					background: linear-gradient(135deg, #fef3c7 0%, #fde68a 100%);
+					color: #d97706;
+				}
+				.filter-modal-title {
+					margin: 0;
+					font-size: 1.25rem;
+					font-weight: 600;
+					color: #1e293b;
+				}
+				.filter-modal-description {
+					margin: 0 0 1rem 0;
+					font-size: 0.875rem;
+					color: #64748b;
+					line-height: 1.5;
+				}
+				.filter-search {
+					width: 100%;
+					padding: 0.625rem 0.875rem;
+					font-size: 0.875rem;
+					border: 1px solid #e2e8f0;
+					border-radius: 8px;
+					margin-bottom: 0.75rem;
+					outline: none;
+					transition: border-color 0.15s;
+				}
+				.filter-search:focus {
+					border-color: #3b82f6;
+					box-shadow: 0 0 0 3px rgba(59, 130, 246, 0.1);
+				}
+				.filter-list {
+					flex: 1;
+					min-height: 200px;
+					max-height: 300px;
+					overflow-y: auto;
+					border: 1px solid #e2e8f0;
+					border-radius: 8px;
+					background: #f8fafc;
+				}
+				.filter-item {
+					display: flex;
+					align-items: center;
+					gap: 0.75rem;
+					padding: 0.625rem 0.875rem;
+					cursor: pointer;
+					transition: background 0.1s;
+					border-bottom: 1px solid #e2e8f0;
+				}
+				.filter-item:last-child {
+					border-bottom: none;
+				}
+				.filter-item:hover {
+					background: #f1f5f9;
+				}
+				.filter-item input[type="checkbox"] {
+					width: 16px;
+					height: 16px;
+					cursor: pointer;
+					accent-color: #3b82f6;
+				}
+				.filter-item-label {
+					flex: 1;
+					font-size: 0.875rem;
+					color: #334155;
+					overflow: hidden;
+					text-overflow: ellipsis;
+					white-space: nowrap;
+				}
+				.filter-loading, .filter-empty {
+					display: flex;
+					align-items: center;
+					justify-content: center;
+					height: 100px;
+					color: #94a3b8;
+					font-size: 0.875rem;
+				}
+				.filter-footer {
+					display: flex;
+					justify-content: space-between;
+					align-items: center;
+					margin-top: 1rem;
+					padding-top: 1rem;
+					border-top: 1px solid #e2e8f0;
+				}
+				.filter-count {
+					font-size: 0.75rem;
+					color: #64748b;
+				}
+				.filter-count strong {
+					color: #3b82f6;
+				}
+				.filter-buttons {
+					display: flex;
+					gap: 0.5rem;
+				}
+				.filter-btn {
+					padding: 0.5rem 1rem;
+					font-size: 0.875rem;
+					font-weight: 500;
+					border-radius: 6px;
+					cursor: pointer;
+					transition: all 0.15s;
+				}
+				.filter-btn-secondary {
+					background: white;
+					color: #475569;
+					border: 1px solid #e2e8f0;
+				}
+				.filter-btn-secondary:hover {
+					background: #f8fafc;
+					border-color: #cbd5e1;
+				}
+				.filter-btn-primary {
+					background: #3b82f6;
+					color: white;
+					border: 1px solid #3b82f6;
+				}
+				.filter-btn-primary:hover {
+					background: #2563eb;
+					border-color: #2563eb;
+				}
+				.filter-btn-clear {
+					background: transparent;
+					color: #ef4444;
+					border: none;
+					padding: 0.5rem;
+					font-size: 0.75rem;
+				}
+				.filter-btn-clear:hover {
+					text-decoration: underline;
+				}
+			`}</style>
+			<div
+				className="filter-modal-overlay"
+				onClick={onClose}
+				onKeyDown={handleKeyDown}
+				role="dialog"
+				aria-modal="true"
+				aria-labelledby={titleId}
+			>
+				{/* biome-ignore lint/a11y/noStaticElementInteractions: modal content wrapper */}
+				<div
+					className="filter-modal"
+					onClick={(e) => e.stopPropagation()}
+					onKeyDown={(e) => e.stopPropagation()}
+				>
+					<div className="filter-modal-header">
+						<div className="filter-modal-icon">
+							<FilterIcon />
+						</div>
+						<h2 id={titleId} className="filter-modal-title">
+							Filter Documents
+						</h2>
+					</div>
+					<p className="filter-modal-description">
+						Select documents to restrict searches. When active, only selected
+						documents will be searched.
+					</p>
+					<input
+						type="text"
+						className="filter-search"
+						placeholder="Search documents..."
+						value={searchTerm}
+						onChange={(e) => setSearchTerm(e.target.value)}
+					/>
+					<div className="filter-list">
+						{loading ? (
+							<div className="filter-loading">Loading documents...</div>
+						) : filteredDocuments.length === 0 ? (
+							<div className="filter-empty">
+								{searchTerm ? "No matching documents" : "No documents found"}
+							</div>
+						) : (
+							filteredDocuments.map((doc) => {
+								const displayName = getDisplayName(doc);
+								return (
+									<label key={doc.id} className="filter-item">
+										<input
+											type="checkbox"
+											checked={localSelected.has(displayName)}
+											onChange={() => toggleDocument(displayName)}
+										/>
+										<span className="filter-item-label">{displayName}</span>
+									</label>
+								);
+							})
+						)}
+					</div>
+					<div className="filter-footer">
+						<div className="filter-count">
+							{localSelected.size > 0 ? (
+								<>
+									<strong>{localSelected.size}</strong> document
+									{localSelected.size === 1 ? "" : "s"} selected
+									<button
+										type="button"
+										className="filter-btn filter-btn-clear"
+										onClick={handleClearAll}
+									>
+										Clear all
+									</button>
+								</>
+							) : (
+								"No filter (all documents)"
+							)}
+						</div>
+						<div className="filter-buttons">
+							<button
+								type="button"
+								className="filter-btn filter-btn-secondary"
+								onClick={onClose}
+							>
+								Cancel
+							</button>
+							<button
+								type="button"
+								className="filter-btn filter-btn-primary"
+								onClick={handleApply}
+							>
+								Apply
+							</button>
+						</div>
+					</div>
+				</div>
+			</div>
+		</>
+	);
+}