What is arcbox copilot-instructions.md?

Project instructions for ArcBox, a Rust-based tool that runs containers and virtual machines on macOS and Linux.

Use them when changing ArcBox's command-line tool, runtime, networking, virtual-machine layers, guest components, or Docker-compatible interface.

They give a coding agent the project's architecture, platform differences, communication methods, and required development practices.

How arcboxlabs/arcbox configures GitHub Copilot

About the project

ArcBox is a Rust runtime for running Docker-compatible containers, disposable microVM sandboxes, and full Linux or macOS virtual machines on macOS. It is used to run AI agents, untrusted code, containers, and isolated machines locally.

arcboxlabs/arcbox · 4,251 stars · on GitHub · arcbox.dev

Reuse

Borrowing it

Nothing to install: this file belongs to arcboxlabs/arcbox. Take a copy, put it at the same path in your own repository, and replace the rules that are about this project with yours.

Copy the file

curl -O https://raw.githubusercontent.com/arcboxlabs/arcbox/master/.github/copilot-instructions.md

Clone the repo

git clone --depth 1 https://github.com/arcboxlabs/arcbox

Made for: GitHub Copilot.

Wrote this? Show the measurements

A badge with what this costs and how it scanned, read live from this page, so it follows the numbers instead of freezing them. Markdown for a README, HTML for a documentation site or a project page.

README.md

[![agentmods](https://agentmods.dev/badge/instructions/arcboxlabs/arcbox/copilot-instructions/github.svg)](https://agentmods.dev/instructions/arcboxlabs/arcbox/copilot-instructions)

Your own site

<a href="https://agentmods.dev/instructions/arcboxlabs/arcbox/copilot-instructions"><img src="https://agentmods.dev/badge/instructions/arcboxlabs/arcbox/copilot-instructions/github.svg" alt="Measured on agentmods" height="20"></a>

Or the 80×15 button, for a site that already has a row of RSS and ATOM ones. Only the verdict fits; the numbers stay here.

Your own site · 80×15

<a href="https://agentmods.dev/instructions/arcboxlabs/arcbox/copilot-instructions"><img src="https://agentmods.dev/badge/instructions/arcboxlabs/arcbox/copilot-instructions.svg" alt="Reviewed on agentmods" width="80" height="20"></a>

Per session 1,576 This file is loaded in full into every session.

When invoked 1,576 The same file — it is already loaded in full.

Security scan A 0 findings. A grade says what 26 rules found in the file — not that it is safe.

Origin original No closer match found in the catalogue.

Token cost

What it costs to keep this loaded

Counted locally with the o200k_base tokenizer, which is exact for GPT models; Claude uses its own tokenizer and its counts differ. Treat this as one consistent yardstick across the catalogue rather than a bill. Prices are per million input tokens.

Model	Per session	Once invoked
Fable 5.1	$0.01576	$0.01576
Opus 5.5	$0.00630	$0.00630
Sonnet 5.5	$0.00315	$0.00315
Haiku 4.5	$0.00158	$0.00158

Measured 2mo ago against content hash e26f712aad53, method: parsed. Prices are Anthropic first-party input rates as of 2026-10-07, from the pricing page.

Security

Grade A, and why

arcbox copilot-instructions.md scanned grade A with 0 findings against 26 rules in 11 categories — prompt injection, anti-refusal, data exfiltration, privilege escalation, supply chain, agent snooping, system-prompt leakage, SSRF and excessive agency — measured 2mo ago.

A static scan of the body, not an audit. Every finding is printed with the line that produced it so you can judge whether it matters here. A mod is markdown that instructs an agent; that is exactly why what it instructs is worth reading.

Nothing flagged

None of the 26 patterns this scan looks for appear in this file: no shell pipes, no recursive deletes, no credential paths, no hidden text, no instruction-override or anti-refusal phrasing, no agent-config snooping. That is not a guarantee, it is the absence of the things that are checkable.

.github/copilot-instructions.md · 173 lines

How it starts

The opening of the file, as written. The whole thing — 173 lines — stays where its author put it; the contents beside it link to each section on GitHub.

ArcBox AI Agent Instructions

ArcBox is a pure-Rust, high-performance container and VM runtime targeting macOS (primary) and Linux, aiming to surpass OrbStack's performance metrics.

Architecture Overview

Three-tier structure:

Core layer (common/, virt/, rpc/, runtime/, app/): MIT/Apache-2.0 licensed foundation
Pro layer (pro/): BSL-1.1 licensed enhanced features (smart caching, snapshots, advanced networking)
Guest components (guest/arcbox-agent): Runs inside VMs, cross-compiled to Linux ARM64/x86_64

Key layers (bottom-up):

abctl (CLI)
    ↓ gRPC over Unix socket
arcbox-daemon
    ↓
arcbox-core (Runtime)
    ↓
arcbox-fs / arcbox-net / arcbox-container
    ↓
arcbox-virtio (VirtIO devices) -> arcbox-vmm (VM monitor)
    ↓
arcbox-hypervisor / arcbox-vz (platform virtualization)

Communication: Host <-> Guest via vsock and ArcBox protocol crates (arcbox-protocol, arcbox-grpc, arcbox-transport). Docker API compatibility is provided by arcbox-docker (Axum REST server + guest dockerd proxy).

Critical Platform Differences

macOS specifics:

Uses Apple's Virtualization.framework (not KVM)
All VM-related binaries require code signing:
```
codesign --entitlements bundle/arcbox.entitlements --force -s - arcbox-daemon
```
Required for: examples, tests touching hypervisor. See arcbox.entitlements
mode_t types (e.g., libc::S_IFMT) are u16 (Linux: u32). Use u32::from() for cross-platform compatibility
No fallocate - use ftruncate instead
xattr APIs have different argument order than Linux

Development Workflows

Building:

cargo build -p <crate>           # Dev build specific crate
cargo build --release            # Full optimized build

Testing:

cargo test -p <crate>
cargo test -- --nocapture        # Show test output
cargo test -- --ignored          # Run privileged tests (require VM access)

Guest agent cross-compilation:

Read the full file on GitHub · 173 lines

Changes

What this file has done since we first saw it

Hashed on every crawl. A supply-chain change to an agent config is a question of when, not whether, so the history is kept rather than the latest state alone.

2mo ago First seen · 173 lines · 1,576 tokens per session scan A e26f712aad53

Subscribe to this mod's changes

arcbox copilot-instructions.md is an instructions file published in the GitHub repository arcboxlabs/arcbox (4,251 stars, last pushed yesterday), licensed Apache-2.0. It adds 1,576 tokens to every session, about $0.0063 per session on Opus 5.5. A static security scan graded it A with 0 findings. No closer match exists in the catalogue, so it is treated as the original; first seen 2026-08-30.

Containers Planning ai-agents computer-use docker firecracker microvm

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arcbox: Instructions file for GitHub Copilot