# Argos –- A 1MB Rust Security Shim for Model Context Protocol Servers

> Source: <https://github.com/JUSICK/Argos-mcp-guardrail>
> Published: 2026-10-07 13:04:17+00:00

Zero-overhead policy enforcement gateway and runtime guardrail for Model Context Protocol (MCP) servers.

`argos` acts as a transparent security pipe between AI clients (Claude Desktop, Cursor) and underlying MCP tool servers. Inspired by the zero-friction philosophy of Quad9/Pi-hole, it inspects raw JSON-RPC traffic on the fly and deterministically blocks unauthorized file access, path traversal attacks, and destructive commands before they reach your system.

- **Sub-millisecond Overhead:** Built with pure Rust and Tokio asynchronous streams. Zero perceptible lag for the agent or developer.
- **Path Traversal Sandboxing:** Enforces strict workspace boundaries via OS path canonicalization and`../` stripping.
- **Secret & Sensitive File Shield:** Block access to`.env` , private keys (`id_rsa` ,`id_ed25519` ), and cloud credentials.
- **Destructive Command Blocker:** Intercepts dangerous terminal commands (`rm -rf` , disk formatters, fork bombs).
- **Local Audit Logging:** Records blocked and allowed actions into a structured, JSON-lines log (`argos-audit.log` ) without cloud telemetry.
- **Flexible Configuration:** Declarative rule customization via`argos.toml` .
- **Your Own Local & Private Tool** : Built entirely in Rust as a self-contained, ~1 MB single binary with zero external telemetry or cloud dependencies. Argos relies strictly on deterministic pattern matching, native OS primitives, and JSON-RPC stream interception—ensuring your sensitive code, configuration keys, and audit trails never leave your local machine.

Download the latest pre-compiled binary for your system from the [Releases](https://github.com/JUSICK/Argos-mcp-guardrail/releases) page:

- **Windows** : Download`argos.exe` (or unpack`argos-windows-x86_64.zip` ).
- **Linux** : Download and extract`argos-linux-x86_64.tar.gz` :

```
tar -xvf argos-linux-x86_64.tar.gz
chmod +x argos
```

If you are running **macOS** (Apple Silicon / Intel) or prefer compiling locally:

```
git clone [https://github.com/JUSICK/Argos-mcp-guardrail.git](https://github.com/JUSICK/Argos-mcp-guardrail.git)
cd Argos-mcp-guardrail
cargo build --release
```

The compiled binary will be located at:

- Linux / macOS: target/release/argos
- Windows: target/release/argos.exe

Create and place `argos.toml` next to the argos executable or in your workspace root:

```
[filesystem]
# Enforce workspace boundary checks
block_path_traversal = true

# Block access to sensitive files and credentials
blocked_patterns = [".env", ".ssh", "id_rsa", "id_ed25519", "credentials", ".aws", ".npmrc"]

# Explicit exceptions allowed through the policy
allowed_patterns = [".env.example", ".env.sample", ".env.template"]

[commands]
# Block destructive terminal commands
blocked_commands = [
  "rm -rf",
  "mkfs",
  ":(){ :|:& };:",
  "chmod -R 777",
  "dd if="
]

[audit]
enabled = true
# Allows to log ALLOWED processes
log_allowed = false
# Just a file name to create one in the same directory where argos is, or full dir
log_file = "argos-audit.log"
```

Update your `claude_desktop_config.json`:

```
{
  "mcpServers": {
    "Argos": {
      "command": "C:\\path\\to\\argos.exe",
      "args": [
        "--",
        "npx.cmd",
        "-y",
        "@modelcontextprotocol/server-filesystem",
        "C:\\Users\\username\\projects\\my-workspace"
      ]
    }
  }
}
{
  "mcpServers": {
    "Argos": {
      "command": "/usr/local/bin/argos",
      "args": [
        "--",
        "npx",
        "-y",
        "@modelcontextprotocol/server-filesystem",
        "/Users/username/projects/my-workspace"
      ]
    }
  }
}
```

Restart Claude Desktop, and Argos will actively guard your tool calls against unauthorized filesystem traversal and credential exposure.

```
[ AI Client (Claude / Cursor) ]
              │
              │ stdin / stdout (JSON-RPC)
              ▼
   ┌───────────────────────┐
   │         argos         │  <── Inspects tools/call in <0.2ms
   └───────────────────────┘
         │           │
   (If Allowed)  (If Blocked) ──> Returns JSON-RPC Error & logs event
         │
         ▼
[ Real MCP Tool Server ]
```

You are able to have as many Argos as you want, change their names e.g. "Argos-Backend", "Argos-Frontend" for a big project that has 2 or more AI agents.

MIT License. Free for personal and commercial use.