fence

Fence wraps commands in a sandbox that blocks network access by default and restricts filesystem operations based on configurable rules. It's most useful for running semi-trusted code (package installs, build scripts, CI jobs, unfamiliar repos) with controlled side effects, and it can also complement AI coding agents as defense-in-depth.

# Block all network access (default)
fence curl https://example.com  # → 403 Forbidden

# Allow specific domains
fence -t code npm install  # → uses 'code' template with npm/pypi/etc allowed

# Block dangerous commands
fence -c "rm -rf /"  # → blocked by command deny rules

Fence is also a permission manager for your CLI agents. Works with popular coding agents like Claude Code, Codex, Amp, Gemini CLI, GitHub Copilot, OpenCode, Factory (Droid) CLI, and many more - see agents.md.

Install

[!NOTE] Fence has moved from github.com/Use-Tusk/fence to github.com/fencesandbox/fence. If you installed with Homebrew from the old Tusk tap, switch to the new tap:

brew uninstall use-tusk/tap/fence
brew untap use-tusk/tap
brew tap fencesandbox/tap
brew install fencesandbox/tap/fence

If you installed with go install, reinstall from the new module path:

go install github.com/fencesandbox/fence/cmd/fence@latest

macOS / Linux:

curl -fsSL https://cli.fencesandbox.com/install.sh | sh

Homebrew (macOS):

brew tap fencesandbox/tap
brew install fencesandbox/tap/fence

Nix (macOS, Linux, Windows (WSL)):

nix run nixpkgs#fence -- --help

This runs it directly from the repository, without installing fence. If you want to install it, follow the guidelines from NixOS or nix-darwin.

Go install:

go install github.com/fencesandbox/fence/cmd/fence@latest

Build from source:

git clone https://github.com/fencesandbox/fence
cd fence
go build -o fence ./cmd/fence

Additional requirements for Linux:

• bubblewrap (for sandboxing)
• socat (for network bridging)
• bpftrace (optional, for filesystem violation visibility when monitoring with -m)

Usage

Basic

# Run command with all network blocked (no domains allowed by default)
fence curl https://example.com

# Run with shell expansion
fence -c "echo hello && ls"

# Enable debug logging
fence -d curl https://example.com

# Use a template
fence -t code -- claude  # Runs Claude Code using `code` template config

# Monitor mode (shows violations)
fence -m npm install

# Send Fence's own monitor/debug logs to a file
fence -m --fence-log-file /tmp/fence.log -- claude
tail -f /tmp/fence.log

# Inspect the config inheritance chain and active merged config
fence config show

# Show all commands and options
fence --help

[!TIP] Need to pass flags to the command you are running? Use -- to separate Fence flags from command flags, for example:

fence -- claude --dangerously-skip-permissions

Configuration

When --settings is not provided, Fence first looks for fence.jsonc (or fence.json) in the current directory and parent directories. If none is found, it falls back to ~/.config/fence/fence.{jsonc,json}. Both extensions are treated as JSONC (comments and trailing commas are allowed). See configuration reference for more details.

{
  "$schema": "https://raw.githubusercontent.com/fencesandbox/fence/main/docs/schema/fence.schema.json",
  "extends": "code",
  "network": { "allowedDomains": ["private.company.com"] },
  "filesystem": { "allowWrite": ["."] },
  "command": { "deny": ["git push", "npm publish"] }
}

For repo-local overrides on top of each user's normal Fence config, use:

{
  "extends": "@base",
  "filesystem": { "allowWrite": ["."] }
}

Use fence --settings ./custom.json to specify a different config.

Inspect the active config without running a command:

fence config show
fence config show --settings ./custom.json
fence config show --template code

fence config show prints the config chain to stderr and the fully resolved config as plain JSON to stdout, so you can pipe the JSON to tools like jq.

Create a starter config with sensible defaults:

# Creates config at the default path with:
# { "extends": "code" }
fence config init

# Include scaffold arrays as editable hints
fence config init --scaffold

Import from Claude Code

fence import --claude --save

Features

• Network isolation - All outbound blocked by default; allowlist domains via config
• Filesystem restrictions - Control read/write access paths
• Command blocking - Deny dangerous commands like rm -rf /, git push
• SSH Command Filtering - Control which hosts and commands are allowed over SSH
• Built-in templates - Pre-configured rulesets for common workflows
• Violation monitoring - Real-time logging of blocked requests (-m)
• Cross-platform - macOS (sandbox-exec) + Linux (bubblewrap)

Fence can be used as a Go package or CLI tool.

Documentation

Full docs are hosted at fencesandbox.com/docs.

Quick links:

• Quickstart (source)
• Configuration Reference (source)
• Agent Hooks (source)
• Security Model (source)
• Go Library Usage (source)
• Architecture (source)

Attribution

Inspired by Anthropic's sandbox-runtime.