# How to Set Up CodeSandbox AI Agent Storage

CodeSandbox AI agent storage bridges ephemeral sandboxes to persistent workspaces. Agents in CodeSandbox need reliable file persistence for iteration and multi-run workflows. Fastio provides generous storage with MCP tools for smooth integration.

CodeSandbox hosts 4 million developers monthly and offers SDK for programmatic sandboxes. However, built-in storage resets on inactivity, limiting agent use cases.

This how-to covers why persistence matters, Fastio features, and step-by-step setup.

Source: https://fast.io/resources/codesandbox-ai-agent-storage/
Last reviewed: 2026-02-19

## What Is CodeSandbox AI Agent Storage?

CodeSandbox AI agent storage enables persistent file handling for agents running in CodeSandbox environments. CodeSandbox sandboxes are ephemeral by design, code runs in isolated VMs or browser contexts that reset on inactivity or closure. Persistence comes from external storage like Fastio workspaces. Agents upload outputs, load datasets, and resume state across sandbox sessions. Key components include CodeSandbox SDK for sandbox management and Fastio MCP tools for file operations (list, read, write, search). Without persistence, agents lose generated files, trained models, or logs between runs. Integration solves this for production workflows.

Helpful references: [Fastio Workspaces](/product/workspaces/), [Fastio Collaboration](/product/collaboration/), and [Fastio AI](/product/ai/).

## Why CodeSandbox Agents Need Persistent Storage

CodeSandbox excels at instant dev environments for prototyping. Its VM sandboxes support full stacks with snapshots for quick resume. However, file storage remains tied to the sandbox lifecycle. Agents require persistence for tasks like iterative code generation, data processing, or multi-step reasoning. A research agent might analyze multiple PDFs over days, losing files mid-task breaks continuity. Common issues without persistence:
* State loss on hibernation (2-second spin-up but data gone)
* No cross-sandbox sharing
* Limited to sandbox disk (credits-based) Fastio fixes this. Agents store artifacts in persistent workspaces, query via RAG, and collaborate with humans.

### Real-World Use Cases

* Content agents: Generate reports, save iterations
* Data agents: Process CSV/JSON across sessions
* Coding agents: Build repos, persist diffs/commits

## Fastio Features for CodeSandbox Agent Storage

Fastio offers cloud storage optimized for agent workflows, starting with a 14-day Business Trial (credit card required) before usage-based plans ($29/mo Starter with 1 TB). A consolidated MCP toolset enables file management, reading, writing, and searches over remote HTTP. Intelligence Mode auto-indexes files for RAG queries. Ownership transfer lets agents build workspaces and humans take over. File version history and granular permissions prevent conflicts in multi-agent swarms while append-only audit logs track all access. Compared to S3 (raw objects) or OpenAI Files (ephemeral), Fastio provides workspaces, previews, and collaboration.

## Step-by-Step: Integrate Fastio with CodeSandbox Agents

Follow these steps to add persistence.

**Step 1: Set up Fastio Agent Account**

Sign up at Fastio to create your account and initialize workspace "codesandbox-agent-storage".

Generate API key from dashboard.

**Step 2: Install CodeSandbox SDK**

In your agent code:

```bash
npm install @codesandbox/sdk
```

**Step 3: Initialize MCP Client for Fastio**

Use MCP or REST client:

```python
from mcp import ClientSession, StdioServerParameters
import asyncio

async def main():
    async with ClientSession(...) as session:
        await session.initialize()
        files = await session.list_files("/", {"glob": "**/*"})
        ### Upload agent output
        await session.write_file("/agent-output/report.json", data)
```

**Step 4: Create Sandbox Programmatically**

Spin sandbox, run agent with Fastio tools:

```javascript
import { Codesandbox } from "@codesandbox/sdk";

const csb = new Codesandbox({ token: "your-token" });
const sandbox = await csb.sandboxes.create({
  template: "node",
  // Agent code uses Fastio MCP
});
```

**Step 5: Test Persistence**

Agent generates file → sandbox hibernates → resume sandbox → file loads.

## Advanced Features

* Webhooks: Notify on file changes (e.g., new threat intel)
* File locks: Acquire before multi-agent writes
* RAG: Query workspace "Summarize recent agent outputs"
* Remote MCP: Connect via Streamable HTTP for natural language tool use

Scale to swarms: One agent per sandbox type, shared Fastio workspace.

## Troubleshooting

* Sandbox credits exhausted: Monitor usage, upgrade tier
* Concurrent write conflicts: Inspect version history to merge changes
* RAG hallucinations: Toggle Intelligence Mode, verify citations
* MCP rate limits: Batch operations, use async

## Frequently asked questions

### What is CodeSandbox AI agent storage?

External persistent storage for files generated by AI agents in CodeSandbox sandboxes. Fastio workspaces provide MCP access, version history, and RAG without data loss on reset.

### Do CodeSandbox agents have built-in persistent files?

No, sandboxes are ephemeral with snapshots for code state only. Files reset on full closure. Integrate Fastio for durable storage across sessions.

### How does Fastio work alongside CodeSandbox?

Use the CodeSandbox SDK to launch sandboxes and connect agents to Fastio via MCP or REST for durable file storage, version history, and RAG search.

### What storage capabilities does the Fastio MCP server provide?

The Fastio MCP server exposes a consolidated toolset for listing files, reading contents, writing uploads, and querying workspace documents.

### What does Fastio cost for agent workloads?

Fastio has no free tier. Workspaces start with a 14-day Business Trial requiring a credit card, transitioning to paid plans starting at $29/mo (Starter with 5 seats and 1 TB).

## About Fast.io

Fast.io provides shared workspaces where people and AI agents work on the same files, with built-in semantic search and citation-backed chat over what they hold. Agents reach it through a remote MCP server at https://mcp.fast.io/mcp, a REST API at https://api.fast.io/current/, and a command line client published on npm as @vividengine/fastio-cli.