Setup: E2B

E2B runs the per-user sandboxes. For Cloud you only need one secret: an API key tied to your team.

Steps

1. Create an account

Sign up at https://e2b.dev. Add a payment method — Cloud's sandbox lifecycle won't work on the free tier past the first couple of minutes (auto-resume needs a paid project).

2. Get the API key

From the dashboard → API keys → Create key. Copy it. This goes into E2B_API_KEY.

Where the variable goes

Variable	.env.local	Vercel
E2B_API_KEY	✓	✓

.env.local is required because you'll be running npm run template:build locally, and the template builder uses the E2B SDK.

How it's used

• Provisioning. When a user first signs in, /workspace calls provisionSandbox() from lib/sandbox.ts which creates an E2B instance from the shmastra template.
• Proxying. The Node route at /api/mastra/[...path] forwards requests into the sandbox on port 4111.
• Lifecycle. After ~10 minutes idle, E2B pauses the sandbox automatically. The next /api/mastra/* request resumes it; work on the filesystem survives pauses.

Quotas

The free account limits concurrent sandboxes and total runtime. For a real team, check your paid plan's limits against:

• Concurrent sandboxes ≥ your expected peak of active users.
• Template size — Shmastra's template is large (Node + Python + Playwright + markitdown + @manzt/uv). Make sure you have headroom.

Next

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