fence
Lightweight, container-free sandbox for running commands with network and filesystem restrictions.
The Lens
By Erik Loyd, SaaS CEO and former COO/CFO of an AWS Premier Partner.
Updated Mar 2026
Fence sandboxes them without containers. It restricts network access and filesystem access at the OS level, so a rogue script can't phone home or delete your files.
What's free: Everything. Apache 2.0 license. Single Go binary, no dependencies, no account.
The value proposition is simplicity. Docker gives you isolation but requires the Docker daemon, images, and significant overhead. Fence is one binary. Run `fence <command>` and it executes with network and filesystem restrictions. That's it. For AI agent sandboxing, where you're running LLM-generated code and need guardrails, this is exactly the right weight class.
The catch: it's brand new and early-stage. Linux only (uses kernel namespaces and seccomp). No macOS or Windows support. The security model is narrower than a full container. It restricts network and filesystem but doesn't provide complete process isolation. For high-security use cases, you still want containers or VMs. For 'don't let this script access the internet or my home directory,' it's perfect.
Free vs Self-Hosted vs Paid
fully freeWhat's Free
Everything. Single binary, Apache 2.0 license. No paid tier, no cloud service, no telemetry.
Total Cost
$0. Download the binary, use it. No infrastructure, no accounts, no recurring costs.
What It Replaces
- Docker (free): Full container isolation but heavy: daemon, images, networking setup. Fence is a single binary.
- Firejail (free): Similar lightweight sandboxing for Linux. More mature but more complex.
- gVisor (free): Google's application kernel. Stronger isolation but significant overhead.
- Firecracker (free): AWS's microVM. Maximum isolation but requires KVM and more setup.
The Trade-off
Fence sits at the 'minimum viable sandbox' point. Less isolation than containers/VMs, dramatically less overhead. The right choice depends on your threat model -- are you protecting against accidental damage or deliberate exploitation?
Completely free. One binary, zero infrastructure. The lightest-weight sandbox you'll find.
What to do by team size
- Solo
- Great for sandboxing AI-generated code or untrusted scripts. Drop it into your workflow in 5 minutes
- Small team
- Useful as a quick guard for CI/CD steps or agent-executed commands. Not a replacement for proper container security
- Medium team
- Consider as a lightweight layer in your agent pipeline. For production isolation, pair with containers or VMs
- Large team
- Too lightweight for enterprise security requirements. Use gVisor, Firecracker, or proper container orchestration
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