diff --git a/src/core/summary.ts b/src/core/summary.ts
new file mode 100644
index 0000000..7e46f3a
--- /dev/null
+++ b/src/core/summary.ts
@@ -0,0 +1,165 @@
+import { getDb } from './db';
+import { isGenAvailable, generate } from './search/ollamaGen';
+
+export interface SummaryData {
+  generatedAt: number;
+  overview: string;
+  components: { title: string; status?: string; summary?: string }[];
+  decisions: { title: string; status?: string }[];
+  tasks: { todo: string[]; in_progress: string[]; done: string[] };
+  memories: { byTag: Record<string, string[]> };
+  stats: { total: number; stale: number; orphans: number; edges: number };
+}
+
+// Ensure cache table exists
+function ensureCacheTable(): void {
+  const db = getDb();
+  db.exec(`
+    CREATE TABLE IF NOT EXISTS system_cache (
+      key TEXT PRIMARY KEY,
+      value TEXT NOT NULL,
+      updated_at INTEGER NOT NULL
+    )
+  `);
+}
+
+export function getCachedSummary(): SummaryData | null {
+  ensureCacheTable();
+  const db = getDb();
+  const row = db.prepare('SELECT value FROM system_cache WHERE key = ?').get('summary') as { value: string } | undefined;
+  if (!row) return null;
+  try {
+    return JSON.parse(row.value);
+  } catch {
+    return null;
+  }
+}
+
+export function cacheSummary(data: SummaryData): void {
+  ensureCacheTable();
+  const db = getDb();
+  db.prepare(`
+    INSERT INTO system_cache (key, value, updated_at) VALUES (?, ?, ?)
+    ON CONFLICT(key) DO UPDATE SET value = excluded.value, updated_at = excluded.updated_at
+  `).run('summary', JSON.stringify(data), Date.now());
+}
+
+export async function generateSummary(): Promise<SummaryData> {
+  const db = getDb();
+  const now = Date.now();
+
+  // Gather all active nodes
+  const rows = db.prepare(`
+    SELECT id, kind, title, status, tags, metadata, content
+    FROM nodes WHERE is_stale = 0
+    ORDER BY kind, title
+  `).all() as any[];
+
+  // Stats
+  const totalNodes = rows.length;
+  const staleCount = (db.prepare('SELECT COUNT(*) as c FROM nodes WHERE is_stale = 1').get() as any).c;
+  const edgeCount = (db.prepare('SELECT COUNT(*) as c FROM edges').get() as any).c;
+
+  const edgeRows = db.prepare('SELECT from_id, to_id FROM edges').all() as any[];
+  const hasEdge = new Set<string>();
+  for (const e of edgeRows) {
+    hasEdge.add(e.from_id);
+    hasEdge.add(e.to_id);
+  }
+  const orphanCount = rows.filter(r => !hasEdge.has(r.id)).length;
+
+  // Categorize nodes
+  const components: SummaryData['components'] = [];
+  const decisions: SummaryData['decisions'] = [];
+  const tasks: SummaryData['tasks'] = { todo: [], in_progress: [], done: [] };
+  const memoryTags: Record<string, string[]> = {};
+
+  for (const row of rows) {
+    const meta = JSON.parse(row.metadata || '{}');
+
+    if (row.kind === 'component') {
+      components.push({
+        title: row.title,
+        status: row.status,
+        summary: meta.summary || (row.content?.slice(0, 100) + (row.content?.length > 100 ? '...' : '')),
+      });
+    } else if (row.kind === 'decision') {
+      decisions.push({ title: row.title, status: row.status });
+    } else if (row.kind === 'task') {
+      const status = (row.status || 'todo').toLowerCase();
+      if (status === 'done' || status === 'completed') {
+        tasks.done.push(row.title);
+      } else if (status === 'in_progress' || status === 'in-progress') {
+        tasks.in_progress.push(row.title);
+      } else {
+        tasks.todo.push(row.title);
+      }
+    } else if (row.kind === 'memory') {
+      const tags: string[] = JSON.parse(row.tags || '[]');
+      // Group by first tag, or 'untagged'
+      const primaryTag = tags[0] || 'untagged';
+      if (!memoryTags[primaryTag]) memoryTags[primaryTag] = [];
+      memoryTags[primaryTag].push(row.title);
+    }
+  }
+
+  // Sort tags by count descending, limit to top 10
+  const sortedTags = Object.entries(memoryTags)
+    .sort((a, b) => b[1].length - a[1].length)
+    .slice(0, 10);
+  const limitedMemoryTags: Record<string, string[]> = {};
+  for (const [tag, titles] of sortedTags) {
+    // Limit to 5 titles per tag
+    limitedMemoryTags[tag] = titles.slice(0, 5);
+    if (titles.length > 5) {
+      limitedMemoryTags[tag].push(`+${titles.length - 5} more`);
+    }
+  }
+
+  // Generate overview
+  let overview: string;
+  const aiAvailable = await isGenAvailable();
+
+  if (aiAvailable) {
+    const prompt = `Write a single sentence (max 30 words) summarizing this knowledge graph for a developer starting a coding session.
+
+Stats: ${totalNodes} nodes (${components.length} components, ${decisions.length} decisions, ${tasks.todo.length + tasks.in_progress.length + tasks.done.length} tasks, ${totalNodes - components.length - decisions.length - tasks.todo.length - tasks.in_progress.length - tasks.done.length} memories), ${edgeCount} edges.
+
+Components: ${components.map(c => c.title).join(', ')}
+Active tasks: ${[...tasks.todo, ...tasks.in_progress].join(', ') || 'none'}
+
+Output ONLY the summary sentence.`;
+
+    const aiOverview = await generate(prompt);
+    overview = aiOverview || buildFallbackOverview(totalNodes, components.length, decisions.length, tasks, edgeCount);
+  } else {
+    overview = buildFallbackOverview(totalNodes, components.length, decisions.length, tasks, edgeCount);
+  }
+
+  const summary: SummaryData = {
+    generatedAt: now,
+    overview,
+    components,
+    decisions,
+    tasks,
+    memories: { byTag: limitedMemoryTags },
+    stats: { total: totalNodes, stale: staleCount, orphans: orphanCount, edges: edgeCount },
+  };
+
+  cacheSummary(summary);
+  return summary;
+}
+
+function buildFallbackOverview(
+  total: number,
+  components: number,
+  decisions: number,
+  tasks: SummaryData['tasks'],
+  edges: number
+): string {
+  const pending = tasks.todo.length + tasks.in_progress.length;
+  const parts = [`${total} nodes`, `${components} components`, `${decisions} decisions`];
+  if (pending > 0) parts.push(`${pending} open tasks`);
+  parts.push(`${edges} edges`);
+  return parts.join(', ') + '.';
+}
diff --git a/src/server/routes.ts b/src/server/routes.ts
index cad09cd..5da4c17 100644
--- a/src/server/routes.ts
+++ b/src/server/routes.ts
@@ -4,6 +4,7 @@ import { getConnections, buildTree } from '../core/graph';
 import { getDb } from '../core/db';
 import { determineGroupingStrategy, groupResults } from './queryOrganizer';
 import { getLastReport, markDirty, runMaintenance } from './heartbeat';
+import { getCachedSummary, generateSummary } from '../core/summary';
 
 const router = Router();
 
@@ -149,6 +150,20 @@ router.post('/query/organize', async (req: Request, res: Response) => {
   }
 });
 
+// Summary — hierarchical pre-computed graph summary
+router.get('/summary', async (req: Request, res: Response) => {
+  try {
+    const refresh = req.query.refresh === 'true';
+    let summary = refresh ? null : getCachedSummary();
+    if (!summary) {
+      summary = await generateSummary();
+    }
+    res.json(summary);
+  } catch (err: any) {
+    res.status(500).json({ error: err.message });
+  }
+});
+
 // Maintenance status
 router.get('/maintenance/status', (_req: Request, res: Response) => {
   const report = getLastReport();