diff --git a/apps/yaak-proxy/components/Sidebar.tsx b/apps/yaak-proxy/components/Sidebar.tsx
index 6117b65cf..6ac820fd6 100644
--- a/apps/yaak-proxy/components/Sidebar.tsx
+++ b/apps/yaak-proxy/components/Sidebar.tsx
@@ -2,8 +2,9 @@ import type { Flow } from "@yaakapp-internal/proxy-lib";
 import type { TreeNode } from "@yaakapp-internal/ui";
 import { selectedIdsFamily, Tree } from "@yaakapp-internal/ui";
 import { atom, useAtomValue } from "jotai";
-import { atomFamily } from "jotai-family";
+import { atomWithStorage } from "jotai/utils";
 import { useCallback } from "react";
+import { applyCollapsed, type CollapsedMap, collapsedMap, folderIds } from "../lib/sidebarCollapse";
 import { flowsAtom, flowTotalAtom } from "../lib/store";
 
 /** A node in the sidebar tree — either a domain or a path segment. */
@@ -14,8 +15,6 @@ export type SidebarItem = {
   count: number;
 };
 
-const collapsedAtom = atomFamily((_treeId: string) => atom<Record<string, boolean>>({}));
-
 export const SIDEBAR_TREE_ID = "proxy-sidebar";
 
 const sidebarTreeAtom = atom<TreeNode<SidebarItem>>((get) => {
@@ -23,6 +22,27 @@ const sidebarTreeAtom = atom<TreeNode<SidebarItem>>((get) => {
   return buildTree(exchanges, get(flowTotalAtom));
 });
 
+/** The domains and paths the user expanded, by node id, kept across launches */
+const expandedAtom = atomWithStorage<Record<string, boolean>>("sidebar_expanded", {}, undefined, {
+  getOnInit: true,
+});
+
+/** The other nodes' collapsed flags, for this launch, as before */
+const otherCollapsedAtom = atom<CollapsedMap>({});
+
+/** Domains and paths collapsed until the user expands them, for the tree */
+const collapsedAtom = atom(
+  (get) =>
+    collapsedMap(folderIds(get(sidebarTreeAtom)), get(expandedAtom), get(otherCollapsedAtom)),
+  (get, set, action: CollapsedMap | ((prev: CollapsedMap) => CollapsedMap)) => {
+    const prev = get(collapsedAtom);
+    const next = typeof action === "function" ? action(prev) : action;
+    const split = applyCollapsed(prev, next, get(expandedAtom), get(otherCollapsedAtom));
+    set(expandedAtom, split.expanded);
+    set(otherCollapsedAtom, split.others);
+  },
+);
+
 /** The sidebar nodes selected, or null when the list shows all traffic */
 const selectedNodeIdsAtom = atom((get) => {
   const selectedIds = get(selectedIdsFamily(SIDEBAR_TREE_ID));
@@ -204,7 +224,7 @@ export function Sidebar() {
     <aside className="x-theme-sidebar bg-surface h-full w-full min-w-0 grid grid-rows-[minmax(0,1fr)] border-r border-border-subtle">
       <Tree
         treeId={treeId}
-        collapsedAtom={collapsedAtom(treeId)}
+        collapsedAtom={collapsedAtom}
         className="px-2 pt-2 pb-10"
         root={tree}
         getItemKey={getItemKey}
diff --git a/apps/yaak-proxy/lib/sidebarCollapse.test.ts b/apps/yaak-proxy/lib/sidebarCollapse.test.ts
new file mode 100644
index 000000000..371ded2f5
--- /dev/null
+++ b/apps/yaak-proxy/lib/sidebarCollapse.test.ts
@@ -0,0 +1,72 @@
+import type { TreeNode } from "@yaakapp-internal/ui";
+import { describe, expect, test } from "vite-plus/test";
+import { applyCollapsed, collapsedMap, folderIds } from "./sidebarCollapse";
+
+/** A node with these children, which `folderIds` counts as a folder when there are any */
+function node(id: string, children: TreeNode<{ id: string }>[] = []): TreeNode<{ id: string }> {
+  return { item: { id }, parent: null, depth: 0, children };
+}
+
+const tree = node("root", [
+  node("domains", [
+    node("domain:api.example.com", [
+      node("path:api.example.com/v1", [node("path:api.example.com/v1/users")]),
+    ]),
+    node("domain:cdn.example.com", [node("path:cdn.example.com/app.js")]),
+    // A host only ever hit at its root has no paths, so nothing to collapse.
+    node("domain:empty.example.com"),
+  ]),
+]);
+
+describe("collapsedMap", () => {
+  test("collapses every domain and path, and leaves the root and Domains open", () => {
+    const map = collapsedMap(folderIds(tree), {}, {});
+    expect(map).toEqual({
+      "domain:api.example.com": true,
+      "path:api.example.com/v1": true,
+      "domain:cdn.example.com": true,
+    });
+    expect(map.root).toBeUndefined();
+    expect(map.domains).toBeUndefined();
+  });
+
+  test("opens what the user expanded, and a host seen later starts collapsed", () => {
+    const expanded = { "domain:api.example.com": true };
+    expect(collapsedMap(folderIds(tree), expanded, {})).toMatchObject({
+      "domain:api.example.com": false,
+      "path:api.example.com/v1": true,
+      "domain:cdn.example.com": true,
+    });
+    const later = node("root", [
+      node("domains", [node("domain:new.example.com", [node("path:new.example.com/x")])]),
+    ]);
+    expect(collapsedMap(folderIds(later), expanded, {})["domain:new.example.com"]).toBe(true);
+  });
+});
+
+describe("applyCollapsed", () => {
+  test("keeps an expanded domain, and forgets it when collapsed again", () => {
+    const prev = collapsedMap(folderIds(tree), {}, {});
+    const opened = applyCollapsed(prev, { ...prev, "domain:api.example.com": false }, {}, {});
+    expect(opened.expanded).toEqual({ "domain:api.example.com": true });
+
+    // Persisted, so the next launch builds the map from it.
+    const relaunched = collapsedMap(folderIds(tree), opened.expanded, {});
+    expect(relaunched["domain:api.example.com"]).toBe(false);
+
+    const closed = applyCollapsed(
+      relaunched,
+      { ...relaunched, "domain:api.example.com": true },
+      opened.expanded,
+      {},
+    );
+    expect(closed.expanded).toEqual({});
+  });
+
+  test("keeps the other nodes' flags apart from the persisted ones", () => {
+    const prev = collapsedMap(folderIds(tree), {}, {});
+    const next = applyCollapsed(prev, { ...prev, domains: true }, {}, {});
+    expect(next).toEqual({ expanded: {}, others: { domains: true } });
+    expect(collapsedMap(folderIds(tree), next.expanded, next.others).domains).toBe(true);
+  });
+});
diff --git a/apps/yaak-proxy/lib/sidebarCollapse.ts b/apps/yaak-proxy/lib/sidebarCollapse.ts
new file mode 100644
index 000000000..0fd788142
--- /dev/null
+++ b/apps/yaak-proxy/lib/sidebarCollapse.ts
@@ -0,0 +1,59 @@
+import type { TreeNode } from "@yaakapp-internal/ui";
+
+/** Flags by node id, as the tree reads them: true is collapsed, and a missing id is open */
+export type CollapsedMap = Record<string, boolean>;
+
+/** Domains and paths start collapsed; the rest, the Domains folder, starts open as before */
+export function startsCollapsed(id: string): boolean {
+  return id.startsWith("domain:") || id.startsWith("path:");
+}
+
+/** Ids of the nodes with children, the only ones that collapse */
+export function folderIds(root: TreeNode<{ id: string }>): string[] {
+  const ids: string[] = [];
+  const walk = (node: TreeNode<{ id: string }>) => {
+    if ((node.children?.length ?? 0) === 0) return;
+    ids.push(node.item.id);
+    for (const child of node.children ?? []) walk(child);
+  };
+  walk(root);
+  return ids;
+}
+
+/**
+ * The tree's collapsed flags: every domain and path collapsed unless the user expanded it, and
+ * other nodes as the user left them.
+ */
+export function collapsedMap(
+  folders: string[],
+  expanded: Record<string, boolean>,
+  others: CollapsedMap,
+): CollapsedMap {
+  const map = { ...others };
+  for (const id of folders) {
+    if (startsCollapsed(id)) map[id] = !expanded[id];
+  }
+  return map;
+}
+
+/**
+ * Splits the flags the tree sets into the domains and paths now expanded, which are kept, and
+ * the other nodes' flags. Only the nodes whose flag changed from `prev` count.
+ */
+export function applyCollapsed(
+  prev: CollapsedMap,
+  next: CollapsedMap,
+  expanded: Record<string, boolean>,
+  others: CollapsedMap,
+): { expanded: Record<string, boolean>; others: CollapsedMap } {
+  const nextExpanded = { ...expanded };
+  const nextOthers = { ...others };
+  for (const id of new Set([...Object.keys(prev), ...Object.keys(next)])) {
+    const collapsed = next[id] === true;
+    if (collapsed === (prev[id] === true)) continue;
+    if (!startsCollapsed(id)) nextOthers[id] = collapsed;
+    else if (collapsed) delete nextExpanded[id];
+    else nextExpanded[id] = true;
+  }
+  return { expanded: nextExpanded, others: nextOthers };
+}
diff --git a/apps/yaak-proxy/package.json b/apps/yaak-proxy/package.json
index cbb2046fc..3c3406794 100644
--- a/apps/yaak-proxy/package.json
+++ b/apps/yaak-proxy/package.json
@@ -18,7 +18,6 @@
     "@yaakapp-internal/ui": "^1.0.0",
     "classnames": "^2.5.1",
     "jotai": "^2.18.0",
-    "jotai-family": "^1.0.1",
     "motion": "^14.0.0",
     "react": "^19.2.0",
     "react-dom": "^19.2.0",
diff --git a/package-lock.json b/package-lock.json
index 0b4fef36f..61d8b58c8 100644
--- a/package-lock.json
+++ b/package-lock.json
@@ -254,7 +254,6 @@
         "@yaakapp-internal/ui": "^1.0.0",
         "classnames": "^2.5.1",
         "jotai": "^2.18.0",
-        "jotai-family": "^1.0.1",
         "motion": "^14.0.0",
         "react": "^19.2.0",
         "react-dom": "^19.2.0",