diff --git a/README.md b/README.md
index c5169c4..d5a8692 100644
--- a/README.md
+++ b/README.md
@@ -509,6 +509,16 @@ npm run build
 npm test
 ```
 
+### Benchmarks
+
+Measure server-side processing overhead with mocked Pinecone responses (no live API calls, no API key required):
+
+```bash
+npm run benchmark
+```
+
+The script prints a table of p50, p95, and p99 latencies in milliseconds and writes results to [`benchmarks/baseline.json`](benchmarks/baseline.json). Compare a new run to the committed baseline (for example with `git diff benchmarks/baseline.json` after re-running the command) to spot regressions.
+
 ### Testing the keyword_search tool
 
 1. **Connectivity and keyword search (script):**  
diff --git a/benchmarks/latency.ts b/benchmarks/latency.ts
new file mode 100644
index 0000000..b04cee2
--- /dev/null
+++ b/benchmarks/latency.ts
@@ -0,0 +1,325 @@
+#!/usr/bin/env tsx
+/**
+ * Local benchmark harness: mocked Pinecone I/O, measures server-side latency (p50/p95/p99).
+ *
+ * Usage: npm run benchmark
+ */
+
+import { writeFileSync } from 'node:fs';
+import { dirname, join } from 'node:path';
+import { fileURLToPath } from 'node:url';
+import { performance } from 'node:perf_hooks';
+import type { McpServer } from '@modelcontextprotocol/sdk/server/mcp.js';
+import { PineconeClient } from '../src/pinecone-client.js';
+import { setLogLevel } from '../src/logger.js';
+import { setPineconeClient } from '../src/server/client-context.js';
+import { invalidateNamespacesCache, getNamespacesWithCache } from '../src/server/namespaces-cache.js';
+import { registerGuidedQueryTool } from '../src/server/tools/guided-query-tool.js';
+import type { MergedHit, PineconeHit, SearchResult, SearchableIndex } from '../src/types.js';
+
+const WARMUP = 10;
+const ITERATIONS = 200;
+const TOP_K = 20;
+
+type BenchmarkResult = {
+  name: string;
+  p50: number;
+  p95: number;
+  p99: number;
+  min: number;
+  max: number;
+  iterations: number;
+};
+
+/** Test double: stub ensureIndexes, searchIndex, rerankResults (no network). */
+type PineconeClientBenchDouble = PineconeClient & {
+  ensureIndexes: () => Promise<{ denseIndex: SearchableIndex; sparseIndex: SearchableIndex }>;
+  searchIndex: (
+    _index: SearchableIndex,
+    _query: string,
+    _topK: number,
+    _namespace?: string,
+    _metadataFilter?: Record<string, unknown>,
+    _options?: { fields?: string[] }
+  ) => Promise<PineconeHit[]>;
+  rerankResults: (_q: string, results: MergedHit[], topN: number) => Promise<SearchResult[]>;
+};
+
+function syntheticHits(prefix: string, count: number, scoreBase: number): PineconeHit[] {
+  const hits: PineconeHit[] = [];
+  for (let i = 0; i < count; i++) {
+    hits.push({
+      _id: `${prefix}-${i}`,
+      _score: scoreBase - i * 0.01,
+      fields: {
+        chunk_text: `Content ${prefix} ${i} lorem ipsum dolor sit amet.`,
+        document_number: `DOC-${prefix}-${i}`,
+        title: `Title ${i}`,
+        url: `https://example.com/${prefix}/${i}`,
+        author: 'bench',
+      },
+    });
+  }
+  return hits;
+}
+
+function percentile(sorted: number[], p: number): number {
+  if (sorted.length === 0) return 0;
+  const idx = Math.ceil((p / 100) * sorted.length) - 1;
+  return sorted[Math.max(0, idx)] ?? 0;
+}
+
+async function runBenchmark(
+  name: string,
+  fn: () => Promise<void>,
+  iterations = ITERATIONS
+): Promise<BenchmarkResult> {
+  for (let w = 0; w < WARMUP; w++) {
+    await fn();
+  }
+  const samples: number[] = [];
+  let min = Number.POSITIVE_INFINITY;
+  let max = Number.NEGATIVE_INFINITY;
+  for (let i = 0; i < iterations; i++) {
+    const t0 = performance.now();
+    await fn();
+    const t1 = performance.now();
+    const ms = t1 - t0;
+    samples.push(ms);
+    min = Math.min(min, ms);
+    max = Math.max(max, ms);
+  }
+  samples.sort((a, b) => a - b);
+  const round4 = (n: number) => Math.round(n * 10000) / 10000;
+  return {
+    name,
+    p50: round4(percentile(samples, 50)),
+    p95: round4(percentile(samples, 95)),
+    p99: round4(percentile(samples, 99)),
+    min: round4(min),
+    max: round4(max),
+    iterations,
+  };
+}
+
+function formatTable(rows: BenchmarkResult[]): string {
+  const headers = ['Scenario', 'p50 (ms)', 'p95 (ms)', 'p99 (ms)', 'min (ms)', 'max (ms)'];
+  const colWidths = [28, 12, 12, 12, 12, 12];
+  const line = (cells: string[]) =>
+    cells.map((c, i) => c.padEnd(colWidths[i])).join(' | ');
+  const out: string[] = [line(headers), line(colWidths.map((w) => '-'.repeat(w)))];
+  for (const r of rows) {
+    out.push(
+      line([
+        r.name.slice(0, colWidths[0] ?? 28),
+        r.p50.toFixed(4),
+        r.p95.toFixed(4),
+        r.p99.toFixed(4),
+        r.min.toFixed(4),
+        r.max.toFixed(4),
+      ])
+    );
+  }
+  return out.join('\n');
+}
+
+function buildQueryBenchClient(): PineconeClientBenchDouble {
+  const denseHits = syntheticHits('dense', TOP_K, 0.95);
+  const sparseHits = syntheticHits('sparse', TOP_K, 0.9);
+  const denseIndexRef = {} as SearchableIndex;
+  const sparseIndexRef = {} as SearchableIndex;
+  const client = new PineconeClient({
+    apiKey: 'bench-key',
+    indexName: 'bench-index',
+    rerankModel: 'bench-rerank',
+  }) as PineconeClientBenchDouble;
+
+  client.ensureIndexes = async () => ({
+    denseIndex: denseIndexRef,
+    sparseIndex: sparseIndexRef,
+  });
+
+  client.searchIndex = async (index) => {
+    if (index === denseIndexRef) return denseHits;
+    if (index === sparseIndexRef) return sparseHits;
+    return [];
+  };
+
+  client.rerankResults = async (_q, results, topN) =>
+    results.slice(0, topN).map((r, i) => ({
+      id: r._id,
+      content: r.chunk_text,
+      score: 1 - i * 0.01,
+      metadata: r.metadata,
+      reranked: true,
+    }));
+
+  return client;
+}
+
+function captureGuidedQueryHandler(): (params: {
+  user_query: string;
+  namespace?: string;
+  metadata_filter?: Record<string, unknown>;
+  top_k: number;
+  preferred_tool: 'auto' | 'count' | 'query_fast' | 'query_detailed';
+  enrich_urls: boolean;
+}) => Promise<unknown> {
+  const handlers = new Map<string, (params: unknown) => Promise<unknown>>();
+  const mockServer = {
+    registerTool: (
+      name: string,
+      _config: unknown,
+      handler: (params: unknown) => Promise<unknown>
+    ) => {
+      handlers.set(name, handler);
+    },
+  } as unknown as McpServer;
+  registerGuidedQueryTool(mockServer);
+  const h = handlers.get('guided_query');
+  if (!h) {
+    throw new Error('guided_query handler not registered');
+  }
+  return h as (params: {
+    user_query: string;
+    namespace?: string;
+    metadata_filter?: Record<string, unknown>;
+    top_k: number;
+    preferred_tool: 'auto' | 'count' | 'query_fast' | 'query_detailed';
+    enrich_urls: boolean;
+  }) => Promise<unknown>;
+}
+
+const benchNamespaceMetadata = {
+  document_number: 'string',
+  title: 'string',
+  url: 'string',
+  author: 'string',
+  chunk_text: 'string',
+} as const;
+
+function createBenchPineconeMock(): PineconeClient {
+  const namespaces = [
+    {
+      namespace: 'docs',
+      recordCount: 1000,
+      metadata: { ...benchNamespaceMetadata },
+    },
+  ];
+
+  const mockQueryResults: SearchResult[] = syntheticHits('mock', 10, 0.9).map((h) => ({
+    id: h._id,
+    content: String(h.fields['chunk_text'] ?? ''),
+    score: h._score,
+    metadata: {
+      document_number: h.fields['document_number'],
+      title: h.fields['title'],
+      url: h.fields['url'],
+      author: h.fields['author'],
+    },
+    reranked: false,
+  }));
+
+  return {
+    async query() {
+      return mockQueryResults;
+    },
+    async count() {
+      return { count: 42, truncated: false };
+    },
+    async listNamespacesWithMetadata() {
+      return namespaces;
+    },
+    async listNamespacesFromKeywordIndex() {
+      return namespaces.map((n) => ({ namespace: n.namespace, recordCount: n.recordCount }));
+    },
+    getSparseIndexName() {
+      return 'bench-index-sparse';
+    },
+    async keywordSearch() {
+      return mockQueryResults;
+    },
+  } as unknown as PineconeClient;
+}
+
+async function main(): Promise<void> {
+  setLogLevel('ERROR');
+  const results: BenchmarkResult[] = [];
+
+  const queryClient = buildQueryBenchClient();
+  results.push(
+    await runBenchmark('query_no_rerank', async () => {
+      await queryClient.query({
+        query: 'benchmark hybrid query text',
+        namespace: 'docs',
+        topK: TOP_K,
+        useReranking: false,
+      });
+    })
+  );
+
+  results.push(
+    await runBenchmark('query_with_rerank', async () => {
+      await queryClient.query({
+        query: 'benchmark hybrid query text',
+        namespace: 'docs',
+        topK: TOP_K,
+        useReranking: true,
+      });
+    })
+  );
+
+  setPineconeClient(createBenchPineconeMock());
+  invalidateNamespacesCache();
+  await getNamespacesWithCache();
+
+  const guidedHandler = captureGuidedQueryHandler();
+  const guidedParams = {
+    user_query: 'list papers about machine learning',
+    top_k: TOP_K,
+    preferred_tool: 'query_fast' as const,
+    enrich_urls: false,
+  };
+
+  results.push(
+    await runBenchmark('guided_query_end_to_end', async () => {
+      await guidedHandler(guidedParams);
+    })
+  );
+
+  results.push(
+    await runBenchmark('list_namespaces_cache_miss', async () => {
+      invalidateNamespacesCache();
+      await getNamespacesWithCache();
+    })
+  );
+
+  results.push(
+    await runBenchmark('list_namespaces_cache_hit', async () => {
+      await getNamespacesWithCache();
+    })
+  );
+
+  const table = formatTable(results);
+  console.log(table);
+  console.log('');
+
+  const payload = {
+    generated_at: new Date().toISOString(),
+    node: process.version,
+    warmup_iterations: WARMUP,
+    measured_iterations: ITERATIONS,
+    results,
+  };
+
+  const __filename = fileURLToPath(import.meta.url);
+  const __dirname = dirname(__filename);
+  const baselinePath = join(__dirname, 'baseline.json');
+  writeFileSync(baselinePath, `${JSON.stringify(payload, null, 2)}\n`, 'utf8');
+  console.log(`Wrote ${baselinePath}`);
+}
+
+main().catch((err) => {
+  console.error(err);
+  process.exit(1);
+});
diff --git a/package.json b/package.json
index 52c8e5a..b982405 100644
--- a/package.json
+++ b/package.json
@@ -44,6 +44,7 @@
     "smoke": "npm run build && node dist/index.js --help",
     "test": "vitest run",
     "test:watch": "vitest",
+    "benchmark": "tsx benchmarks/latency.ts",
     "test:search": "tsx scripts/test-search.ts",
     "test:mcp": "node test-mcp-server.js",
     "lint": "eslint src/",