> ## Documentation Index
> Fetch the complete documentation index at: https://docs.hexr.dev/llms.txt
> Use this file to discover all available pages before exploring further.

# Code Execution in Sandbox

> Run untrusted code safely in Firecracker microVMs with hexr.sandbox.

## Why Sandbox?

AI agents often need to execute generated code — data analysis, web scraping, calculations. Running this directly is dangerous. Hexr Sandbox provides:

* **Firecracker microVM** isolation
* **No network access** by default
* **Resource limits** (CPU, memory, time)
* **Destroyed after execution** (no persistent state)

***

## Basic Usage

```python theme={null}
from hexr import hexr_agent
from hexr.sandbox import exec

@hexr_agent(name="data-analyst", tenant="acme-corp")
def main():
    result = exec("""
import pandas as pd
import numpy as np

data = pd.DataFrame({
    'revenue': [100, 200, 150, 300, 250],
    'costs': [80, 150, 100, 200, 180],
})
data['profit'] = data['revenue'] - data['costs']
print(data.describe().to_string())
print(f"\\nTotal profit: ${data['profit'].sum()}")
""")
    
    print(result.stdout)
    # →         revenue  costs  profit
    #   count     5.00   5.00    5.00
    #   mean    200.00 142.00   58.00
    #   ...
    #   Total profit: $290
```

***

## LLM + Sandbox Pattern

A common pattern: ask an LLM to generate code, then execute it safely:

```python theme={null}
from hexr import hexr_agent, hexr_llm
from hexr.sandbox import exec

@hexr_agent(name="code-agent", tenant="acme-corp")
def main():
    # Ask LLM to generate analysis code
    code = hexr_llm(
        provider="openai",
        model="gpt-4o",
        prompt="Write Python code to calculate the first 20 Fibonacci numbers",
    )
    
    # Execute safely in a microVM
    result = exec(code, language="python", timeout=10)
    
    if result.exit_code == 0:
        print(f"Output: {result.stdout}")
    else:
        print(f"Error: {result.stderr}")
```

***

## Multi-Language Support

```python theme={null}
# Python
result = exec("print('Hello from Python')", language="python")

# JavaScript
result = exec("console.log('Hello from Node.js')", language="javascript")

# Shell
result = exec("echo 'Hello from Bash' && uname -a", language="bash")
```

***

## Resource Limits

```python theme={null}
result = exec(
    code="...",
    language="python",
    timeout=60,          # Max 60 seconds
    memory_mb=512,       # Max 512MB RAM
)
```

***

## Security Guarantees

| Threat                   | Protection                             |
| ------------------------ | -------------------------------------- |
| Code escapes to host     | Firecracker KVM isolation              |
| Network exfiltration     | No network by default                  |
| Disk persistence         | Read-only rootfs, destroyed after exec |
| Resource exhaustion      | CPU + memory + time limits             |
| Cross-agent interference | Separate microVM per execution         |