dcg

DCG — Destructive Command Guard

A high-performance Claude Code hook that intercepts and blocks destructive commands before they execute. Written in Rust with SIMD-accelerated filtering for sub-millisecond latency.

Why This Exists

AI coding agents are powerful but fallible. They can accidentally run destructive commands:

• "Let me clean up the build artifacts" → rm -rf ./src (typo)
• "I'll reset to the last commit" → git reset --hard (destroys uncommitted changes)
• "Let me fix the merge conflict" → git checkout -- . (discards all modifications)
• "I'll clean up untracked files" → git clean -fd (permanently deletes untracked files)

DCG intercepts dangerous commands before execution and blocks them with a clear explanation, giving you a chance to stash your changes first.

Critical Design Principles

1. Whitelist-First Architecture

Safe patterns are checked before destructive patterns. This ensures explicitly safe commands are never accidentally blocked:

git checkout -b feature    →  Matches SAFE "checkout-new-branch"  →  ALLOW
git checkout -- file.txt   →  No safe match, matches DESTRUCTIVE  →  DENY

2. Fail-Safe Defaults (Default-Allow)

Unrecognized commands are allowed by default. This ensures:

• The hook never breaks legitimate workflows
• Only known dangerous patterns are blocked
• New git commands work until explicitly categorized

3. Zero False Negatives Philosophy

The pattern set prioritizes never allowing dangerous commands over avoiding false positives. A few extra prompts for manual confirmation are acceptable; lost work is not.

What It Blocks

Git Commands That Destroy Uncommitted Work

| Command | Reason | |---------|--------| | git reset --hard | Destroys uncommitted changes | | git reset --merge | Destroys uncommitted changes | | git checkout -- <file> | Discards file modifications | | git restore <file> (without --staged) | Discards uncommitted changes | | git clean -f | Permanently deletes untracked files |

Git Commands That Destroy Remote History

| Command | Reason | |---------|--------| | git push --force / -f | Overwrites remote commits | | git branch -D | Force-deletes without merge check |

Git Commands That Destroy Stashed Work

| Command | Reason | |---------|--------| | git stash drop | Permanently deletes a stash | | git stash clear | Permanently deletes all stashes |

Filesystem Commands

| Command | Reason | |---------|--------| | rm -rf (outside /tmp, /var/tmp, $TMPDIR) | Recursive deletion is dangerous |

What It ALLOWS

Safe operations pass through silently:

Always Safe Git Operations

git status, git log, git diff, git add, git commit, git push, git pull, git fetch, git branch -d (safe delete with merge check), git stash, git stash pop, git stash list

Explicitly Safe Patterns

| Pattern | Why Safe | |---------|----------| | git checkout -b <branch> | Creating new branches | | git checkout --orphan <branch> | Creating orphan branches | | git restore --staged <file> | Unstaging only, doesn't touch working tree | | git restore -S <file> | Short flag for staged | | git clean -n / --dry-run | Preview mode, no actual deletion | | rm -rf /tmp/ | Temp directories are ephemeral | | rm -rf $TMPDIR/ | Shell variable forms |

Safe Alternative: --force-with-lease

git push --force-with-lease   # ALLOWED - refuses if remote has unseen commits
git push --force              # BLOCKED - can overwrite others' work

Modular Pack System

DCG uses a modular "pack" system to organize patterns by category:

Core Packs (Always Enabled)

| Pack | Description | |------|-------------| | core.git | Destructive git commands | | core.filesystem | Dangerous rm -rf outside temp |

Database Packs

| Pack | Description | |------|-------------| | database.postgresql | DROP/TRUNCATE in PostgreSQL | | database.mysql | DROP/TRUNCATE in MySQL/MariaDB | | database.mongodb | dropDatabase, drop() | | database.redis | FLUSHALL/FLUSHDB | | database.sqlite | DROP in SQLite |

Container Packs

| Pack | Description | |------|-------------| | containers.docker | docker system prune, docker rm -f | | containers.compose | docker-compose down --volumes | | containers.podman | podman system prune |

Kubernetes Packs

| Pack | Description | |------|-------------| | kubernetes.kubectl | kubectl delete namespace | | kubernetes.helm | helm uninstall | | kubernetes.kustomize | kustomize delete patterns |

Cloud Provider Packs

| Pack | Description | |------|-------------| | cloud.aws | Destructive AWS CLI commands | | cloud.gcp | Destructive gcloud commands | | cloud.azure | Destructive az commands |

Infrastructure Packs

| Pack | Description | |------|-------------| | infrastructure.terraform | terraform destroy | | infrastructure.ansible | Dangerous ansible patterns | | infrastructure.pulumi | pulumi destroy |

System Packs

| Pack | Description | |------|-------------| | system.disk | dd, mkfs, fdisk operations | | system.permissions | Dangerous chmod/chown patterns | | system.services | systemctl stop/disable patterns |

Other Packs

| Pack | Description | |------|-------------| | strict_git | Extra paranoid git protections | | package_managers | npm unpublish, cargo yank |

Configuring Packs

# ~/.config/dcg/config.toml
[packs]
enabled = [
    "database.postgresql",
    "containers.docker",
    "kubernetes",  # Enables all kubernetes sub-packs
]

Environment Variables

| Variable | Description | |----------|-------------| | DCG_PACKS="containers.docker,kubernetes" | Enable packs (comma-separated) | | DCG_DISABLE="kubernetes.helm" | Disable packs/sub-packs | | DCG_VERBOSE=1 | Verbose output | | DCG_COLOR=auto\|always\|never | Color mode | | DCG_BYPASS=1 | Bypass DCG entirely (escape hatch) |

Installation

Quick Install (Recommended)

curl -fsSL "https://raw.githubusercontent.com/Dicklesworthstone/destructive_command_guard/master/install.sh?$(date +%s)" | bash

# Easy mode: auto-update PATH
curl -fsSL "https://raw.githubusercontent.com/Dicklesworthstone/destructive_command_guard/master/install.sh?$(date +%s)" | bash -s -- --easy-mode

# System-wide (requires sudo)
curl -fsSL "https://raw.githubusercontent.com/Dicklesworthstone/destructive_command_guard/master/install.sh?$(date +%s)" | sudo bash -s -- --system

From Source (Requires Rust Nightly)

cargo +nightly install --git https://github.com/Dicklesworthstone/destructive_command_guard

Prebuilt Binaries

Available for: Linux x86_64, Linux ARM64, macOS Intel, macOS Apple Silicon, Windows

Claude Code Configuration

Add to ~/.claude/settings.json:

{
  "hooks": {
    "PreToolUse": [
      {
        "matcher": "Bash",
        "hooks": [
          {
            "type": "command",
            "command": "dcg"
          }
        ]
      }
    ]
  }
}

Important: Restart Claude Code after adding the hook.

How It Works

Processing Pipeline

┌─────────────────────────────────────────────────────────────────┐
│                        Claude Code                               │
│  Agent executes `rm -rf ./build`                                │
└─────────────────────┬───────────────────────────────────────────┘
                      │
                      ▼ PreToolUse hook (stdin: JSON)
┌─────────────────────────────────────────────────────────────────┐
│                          dcg                                     │
│  ┌──────────────┐    ┌──────────────┐    ┌──────────────┐       │
│  │    Parse     │───▶│  Normalize   │───▶│ Quick Reject │       │
│  │    JSON      │    │   Command    │    │   Filter     │       │
│  └──────────────┘    └──────────────┘    └──────┬───────┘       │
│                                                  │