# Best sandbox for Mastra agents in 2027

Runtime Cloud (withruntime.com) adds a Mastra agent as plain tools. It costs 68% less than Vercel Sandbox.

## Which sandbox is best for Mastra?

It depends on whether you want Mastra's workspace layer. For per-user agents
added as plain tools, Runtime has the lowest cost of the sandboxes priced
below: $34.17 for twenty thousand data questions,
compared with $106.13 on Vercel Sandbox and
$165.60 on E2B. It bills measured CPU, and each user's
sandbox pauses with its memory kept. Pick a workspace provider Mastra lists,
such as Vercel, Daytona or E2B, for Mastra's filesystem abstraction and
mounts. Keep LocalSandbox for code you trust.

## How does Mastra connect an agent to a sandbox?

Mastra has two routes. Its workspaces attach a sandbox provider to an agent
with `workspace: new Workspace({ sandbox })`. Mastra's
[sandbox docs](https://mastra.ai/docs/sandbox/overview) list Daytona, E2B,
Modal, Vercel and Docker among the providers. Separately, any AI SDK tool can
go straight into an agent's `tools`. It needs no workspace and no provider
package, and the same tools work in a plain `generateText` call.

| Route                                 | Where commands run            | What you add                        |
| ------------------------------------- | ----------------------------- | ----------------------------------- |
| `LocalSandbox`, no isolation          | The app's own host            | Nothing; Mastra calls it not secure |
| `LocalSandbox` with bwrap or seatbelt | The host, with writes limited | Bubblewrap or macOS Seatbelt        |
| A workspace sandbox provider          | That provider's machines      | The provider's Mastra package       |

## What matters in a sandbox for Mastra?

- **Per-user machines that cost nothing idle.** A Mastra app usually serves
  many users. One named sandbox per user pauses when nothing happens. It
  resumes with its files, memory and processes when that user returns. This
  keeps each user's work apart and keeps idle hours cheap.
- **Packages without a build step.** An image with Python, Node.js and the
  data libraries in place, where `pip install` works when the agent needs
  more.
- **Steps that can take a while.** A command runs up to the timeout you
  give it, so a long data job is one tool call, not a polling loop.
- **One tool set across frameworks.** Sandbox tools written as AI SDK tools
  serve a Mastra agent, an AI SDK route and a workflow step alike.

## What does a Mastra data agent cost per month?

Twenty thousand questions, each three minutes on a 2 vCPU, 4 GiB sandbox and
busy for 30 CPU-seconds, at each provider's published rates:

| Provider       | Isolation               | CPU billed on     | A month of questions              |
| -------------- | ----------------------- | ----------------- | --------------------------------- |
| Runtime Cloud  | Firecracker microVM     | Measured use      | $34.17 |
| Vercel Sandbox | Firecracker microVM     | Measured use      | $106.13  |
| E2B            | Firecracker microVM     | Every vCPU held   | $165.60     |
| Daytona        | Containers by default   | Every vCPU held   | $165.60 |
| Modal          | gVisor, a shared kernel | The CPU requested | $237.96   |

## When might another sandbox fit better?

- **Mastra's workspace features.** If you want Mastra's workspace layer
  itself, with its filesystem abstraction and mounts, use one of the workspace
  providers Mastra lists. Runtime connects as tools instead.

## Runtime Cloud

With Runtime, a Mastra agent gets a full Linux microVM from one line,
`tools: runtimeTools(sbx)` from `withruntime`. It pays for CPU only while
code runs. The four tools run commands and read, write and list files in a
Firecracker microVM with its own kernel.

- `Sandbox.getOrCreate("user-42")` gives each user one named sandbox. It
  pauses itself after 300 seconds with nothing happening.
- The default image has Python 3.12, Node.js 24, pandas, NumPy and
  matplotlib.
- The tools are AI SDK tools, so the same sandbox code serves a Mastra agent,
  an AI SDK route and a workflow step.

The twenty thousand questions above cost $34.17 on
Runtime, 68% less than Vercel Sandbox and
86% less than Modal, at rates checked
25 October 2026.

### A run on Runtime, recorded 1 October 2026

```ts check
import { Agent } from "@mastra/core/agent";
import { Sandbox } from "withruntime";
import { runtimeTools } from "withruntime/ai";

await using sbx = await Sandbox.create();
const analyst = new Agent({
  id: "analyst",
  name: "Analyst",
  instructions: "Answer with numbers you computed in the sandbox.",
  model: "anthropic/claude-sonnet-4-6",
  tools: runtimeTools(sbx),
});
const answer = await analyst.generate("Total revenue by region in sales.csv?", { maxSteps: 6 });
console.log(answer.text);
```

We ran this agent's `generate()` loop with `@mastra/core` 1.71.0 and the AI
SDK's mock model in place of Claude. The model's two tool calls were
scripted, and Mastra ran them against a live sandbox:

```text
runtime_write_file sales.csv   Wrote 62 bytes to /workspace/sales.csv
runtime_exec python3 -c "...groupby('region').revenue.sum()..."
  exitCode 0
  region
  east     1250
  south     950
  west     1500
```

pandas was there with nothing installed first. Per-user sandboxes and the
rest of the API are in [Mastra in a sandbox](/integrations/mastra).

Sign in with `npx withruntime login`, and the agent above runs on free usage.
Tools that already call the E2B, Daytona or Vercel Sandbox SDK move with the
[migration guide](/docs/migrate).

## Sources

Checked 25 October 2026.

- [Mastra sandboxes](https://mastra.ai/docs/sandbox/overview): workspaces,
  the provider list and the `LocalSandbox` isolation levels
- Each provider's published rates, checked 25 October 2026, as the
  [pricing guide](/docs/pricing) lists them
- The recorded run: Runtime's TypeScript SDK with `@mastra/core` 1.71.0 and
  `ai` 7.0.87's `MockLanguageModelV4`, against production on 1 October 2026