diff --git a/apps/yaak-proxy/Sidebar.tsx b/apps/yaak-proxy/Sidebar.tsx
new file mode 100644
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--- /dev/null
+++ b/apps/yaak-proxy/Sidebar.tsx
@@ -0,0 +1,169 @@
+import type { HttpExchange } from "@yaakapp-internal/proxy-lib";
+import { Tree } from "@yaakapp-internal/ui";
+import type { TreeNode } from "@yaakapp-internal/ui";
+import { atom, useAtomValue } from "jotai";
+import { atomFamily } from "jotai/utils";
+import { useCallback, useMemo } from "react";
+import { httpExchangesAtom } from "./store";
+
+/** A node in the sidebar tree — either a domain or a path segment. */
+export type SidebarItem = {
+  id: string;
+  label: string;
+  exchangeIds: string[];
+};
+
+const collapsedAtom = atomFamily((treeId: string) =>
+  atom<Record<string, boolean>>({}),
+);
+
+const sidebarTreeAtom = atom<TreeNode<SidebarItem>>((get) => {
+  const exchanges = get(httpExchangesAtom);
+  return buildTree(exchanges);
+});
+
+/**
+ * Build a domain → path-segment trie from a flat list of exchanges.
+ *
+ * Example: Given URLs
+ *   GET https://api.example.com/v1/users
+ *   GET https://api.example.com/v1/users/123
+ *   POST https://api.example.com/v1/orders
+ *
+ * Produces:
+ *   api.example.com
+ *     /v1
+ *       /users
+ *         /123
+ *       /orders
+ */
+function buildTree(exchanges: HttpExchange[]): TreeNode<SidebarItem> {
+  const root: SidebarItem = { id: "root", label: "All Traffic", exchangeIds: [] };
+  const rootNode: TreeNode<SidebarItem> = {
+    item: root,
+    parent: null,
+    depth: 0,
+    children: [],
+  };
+
+  // Intermediate trie structure for building
+  type TrieNode = {
+    id: string;
+    label: string;
+    exchangeIds: string[];
+    children: Map<string, TrieNode>;
+  };
+
+  const domainMap = new Map<string, TrieNode>();
+
+  for (const ex of exchanges) {
+    let hostname: string;
+    let segments: string[];
+    try {
+      const url = new URL(ex.url);
+      hostname = url.host;
+      segments = url.pathname.split("/").filter(Boolean);
+    } catch {
+      hostname = ex.url;
+      segments = [];
+    }
+
+    // Get or create domain node
+    let domainNode = domainMap.get(hostname);
+    if (!domainNode) {
+      domainNode = {
+        id: `domain:${hostname}`,
+        label: hostname,
+        exchangeIds: [],
+        children: new Map(),
+      };
+      domainMap.set(hostname, domainNode);
+    }
+    domainNode.exchangeIds.push(ex.id);
+
+    // Walk path segments
+    let current = domainNode;
+    const pathSoFar: string[] = [];
+    for (const seg of segments) {
+      pathSoFar.push(seg);
+      let child = current.children.get(seg);
+      if (!child) {
+        child = {
+          id: `path:${hostname}/${pathSoFar.join("/")}`,
+          label: `/${seg}`,
+          exchangeIds: [],
+          children: new Map(),
+        };
+        current.children.set(seg, child);
+      }
+      child.exchangeIds.push(ex.id);
+      current = child;
+    }
+  }
+
+  // Convert trie to TreeNode structure
+  function toTreeNode(
+    trie: TrieNode,
+    parent: TreeNode<SidebarItem>,
+    depth: number,
+  ): TreeNode<SidebarItem> {
+    const node: TreeNode<SidebarItem> = {
+      item: {
+        id: trie.id,
+        label: trie.label,
+        exchangeIds: trie.exchangeIds,
+      },
+      parent,
+      depth,
+      children: [],
+    };
+    for (const child of trie.children.values()) {
+      node.children!.push(toTreeNode(child, node, depth + 1));
+    }
+    return node;
+  }
+
+  // Sort domains alphabetically, add to root
+  const sortedDomains = [...domainMap.values()].sort((a, b) =>
+    a.label.localeCompare(b.label),
+  );
+  for (const domain of sortedDomains) {
+    rootNode.children!.push(toTreeNode(domain, rootNode, 1));
+  }
+
+  return rootNode;
+}
+
+function ItemInner({ item }: { item: SidebarItem }) {
+  const count = item.exchangeIds.length;
+  return (
+    <div className="flex items-center gap-2 w-full min-w-0">
+      <span className="truncate">{item.label}</span>
+      {count > 0 && (
+        <span className="text-text-subtlest text-2xs shrink-0">{count}</span>
+      )}
+    </div>
+  );
+}
+
+export function Sidebar() {
+  const tree = useAtomValue(sidebarTreeAtom);
+  const treeId = "proxy-sidebar";
+
+  const getItemKey = useCallback((item: SidebarItem) => item.id, []);
+
+  return (
+    <aside className="x-theme-sidebar h-full w-[250px] min-w-0 overflow-y-auto border-r border-border-subtle">
+      <div className="pt-2 text-xs">
+        <Tree
+          treeId={treeId}
+          collapsedAtom={collapsedAtom(treeId)}
+          className="px-2 pb-10"
+          root={tree}
+          getItemKey={getItemKey}
+          ItemInner={ItemInner}
+        />
+      </div>
+    </aside>
+  );
+}