---
title: "WASM Sandbox"
description: "Every agent runs in a WebAssembly sandbox for security and isolation. The WASM sandbox ensures agents: Cannot access the host file system Cannot make network requests (unless granted) Cannot read environment variables (u"
resource: https://www.aiagents.nexus/docs/manual/agents/wasm-sandbox
generated: { by: "process:nexus-agent-assets", at: 2026-09-07T09:13:03Z }
status: stable
---

# WASM Sandbox

Every agent runs in a WebAssembly sandbox for security and isolation.

## What is Sandboxing?

The WASM sandbox ensures agents:
- Cannot access the host file system
- Cannot make network requests (unless granted)
- Cannot read environment variables (unless granted)
- Cannot access other agents' memory
- Cannot spawn processes

## Capability Model

Agents start with zero capabilities. You grant what they need:

```yaml
agents:
  researcher:
    template: researcher
    capabilities:
      network: true       # Allow HTTP requests
      fileRead: true      # Allow reading files
      fileWrite: false    # No file writing
      env:                # Specific env vars
        - API_KEY
        - MODEL
```

## Resource Limits

| Resource | Default | Configurable |
|----------|---------|-------------|
| Fuel (CPU) | 1,000,000 | Yes |
| Memory | 16 MB (256 pages) | Yes |
| Stack | 1 MB | No |
| Instances | 100 concurrent | Yes |

```yaml
agents:
  researcher:
    wasm:
      fuel: 5000000        # 5x default
      memoryPages: 512     # 32 MB
```

## Fuel System

Fuel is the WASM equivalent of CPU time. Every instruction consumes fuel. When fuel runs out, the agent is paused.

```
Start: fuel = 1,000,000
  │
  ├── instruction 1: fuel = 999,999
  ├── instruction 2: fuel = 999,998
  │   ...
  └── fuel = 0 → agent paused
```

This prevents infinite loops and ensures predictable resource usage.

## Security Model

```
┌─────────────────────────────┐
│        Host System          │
│  ┌───────────────────────┐  │
│  │    WASM Sandbox       │  │
│  │  ┌─────────────────┐  │  │
│  │  │    Agent Code   │  │  │
│  │  │                 │  │  │
│  │  │  No FS access   │  │  │
│  │  │  No net access  │  │  │
│  │  │  No env access  │  │  │
│  │  └─────────────────┘  │  │
│  │                       │  │
│  │  Granted capabilities │  │
│  │  only via host calls  │  │
│  └───────────────────────┘  │
└─────────────────────────────┘
```