diff --git a/nextjs/.env.example b/nextjs/.env.example
index 4b9fc86..733a4ed 100644
--- a/nextjs/.env.example
+++ b/nextjs/.env.example
@@ -1,3 +1,6 @@
 # Set in your Vercel project environment variables.
 # For local dev: add to .env.local (never commit this file)
+#
+# The app reads KAK_API_KEY or KAKUNIN_API_KEY. The Vercel Marketplace
+# integration injects KAK_API_KEY automatically; for local dev set either.
 KAKUNIN_API_KEY=kak_live_...
diff --git a/nextjs/README.md b/nextjs/README.md
index baceff1..757b28a 100644
--- a/nextjs/README.md
+++ b/nextjs/README.md
@@ -4,7 +4,7 @@ Full-stack example: agent registration, certificate issuance, and middleware-lev
 
 ## What this covers
 
-- `lib/kakunin.ts` — singleton SDK init (reads `KAK_API_KEY` from env)
+- `lib/kakunin.ts` — singleton SDK init (reads `KAK_API_KEY` or `KAKUNIN_API_KEY` from env)
 - `app/api/v1/agents/route.ts` — register + certify an agent via POST
 - `middleware.ts` — enforce cert serial on all `/api/agent/*` routes
 
diff --git a/nextjs/lib/kakunin.ts b/nextjs/lib/kakunin.ts
index d16e8e4..bef15e6 100644
--- a/nextjs/lib/kakunin.ts
+++ b/nextjs/lib/kakunin.ts
@@ -1,8 +1,16 @@
 import Kakunin from '@kakunin/sdk';
 
 // Singleton — reuse across requests in the same serverless function instance.
-// KAKUNIN_API_KEY is set in your Vercel project environment variables.
-// Use kak_live_... for production, kak_test_... for sandbox.
-export const kkn = new Kakunin({
-  apiKey: process.env.KAKUNIN_API_KEY!,
-});
+// The API key comes from your environment. The Vercel Marketplace integration
+// injects KAK_API_KEY; local dev / the Deploy button use KAKUNIN_API_KEY. We
+// accept either so both paths work. Use kak_live_... for production,
+// kak_test_... for sandbox.
+const apiKey = process.env.KAK_API_KEY ?? process.env.KAKUNIN_API_KEY;
+if (!apiKey) {
+  throw new Error(
+    'Missing Kakunin API key. Set KAKUNIN_API_KEY (or KAK_API_KEY via the ' +
+      'Vercel Marketplace integration). Get one at https://kakunin.ai/dashboard/api-keys',
+  );
+}
+
+export const kkn = new Kakunin({ apiKey });