Parry

Prompt injection scanner for Claude Code hooks. Scans tool inputs and outputs for injection attacks, secrets, and data exfiltration attempts.

Early development — this tool is under active development and may have bugs or false positives. Tested on linux/macOS.

Prerequisites

The ML models are gated on HuggingFace. Before installing:

1. Create an account at huggingface.co
2. Accept the DeBERTa v3 license (required for all modes)
3. For full mode: also accept the Llama Prompt Guard 2 license (Meta approval required)
4. Create an access token at huggingface.co/settings/tokens

Install

cargo-binstall

cargo binstall parry-ai

From source

# Default (Candle backend - pure Rust, no native deps)
cargo install --path crates/cli

# ONNX backend (faster inference, needs native libs)
cargo install --path crates/cli --no-default-features --features onnx-fetch

Nix (home-manager)

# flake.nix
{
  inputs.parry.url = "github:vaporif/parry";

  outputs = { parry, ... }: {
    # pass parry to your home-manager config via extraSpecialArgs, overlays, etc.
  };
}

# home-manager module
{ inputs, pkgs, config, ... }: {
  imports = [ inputs.parry.homeManagerModules.default ];

  programs.parry = {
    enable = true;
    package = inputs.parry.packages.${pkgs.system}.default;  # candle (default)
    # package = inputs.parry.packages.${pkgs.system}.onnx;  # onnx backend (5-7x faster, see Performance)
    hfTokenFile = config.sops.secrets.hf-token.path;
    ignorePaths = [ "/home/user/repos/parry" ];

    # scanMode = "full";  # fast (default) | full | custom

    # Custom models (auto-sets scanMode to "custom")
    # models = [
    #   { repo = "ProtectAI/deberta-v3-small-prompt-injection-v2"; }
    #   { repo = "meta-llama/Llama-Prompt-Guard-2-86M"; threshold = 0.5; }
    # ];
  };
}

You still need to configure the Claude Code hook separately (see below).

Setup

1. Configure HuggingFace token

One of (first match wins):

export HF_TOKEN="hf_..."                          # direct value
export HF_TOKEN_PATH="/path/to/token"              # file path
# or place token at /run/secrets/hf-token-scan-injection

2. Add Claude Code hook

Add to ~/.claude/settings.json:

{
  "hooks": {
    "PreToolUse": [{ "command": "parry hook", "timeout": 1000 }],
    "PostToolUse": [{ "command": "parry hook", "timeout": 5000 }],
    "UserPromptSubmit": [{ "command": "parry hook", "timeout": 2000 }]
  }
}

The daemon auto-starts on first scan, downloads the model on first run, and idles out after 30 minutes.

Note (non-Nix users): The Nix home-manager module wraps the binary with all config baked in via env vars. Without Nix, set env vars in your shell profile (e.g. HF_TOKEN, PARRY_IGNORE_PATHS, PARRY_SCAN_MODE) — the hook command inherits them. Alternatively, pass flags directly in the hook command: parry --hf-token-path ~/.hf-token --ignore-path /home/user/safe hook. See Config for all options.

What each hook does

• PreToolUse: 5-layer security — taint enforcement, CLAUDE.md scanning, exfil blocking, sensitive path blocking, input content injection scanning (Write/Edit/Bash/MCP tools)
• PostToolUse: Scans tool output for injection/secrets, auto-taints project on detection
• UserPromptSubmit: Audits .claude/ directory for dangerous permissions, injected commands, hook scripts

Daemon & Cache

The daemon keeps ML models in memory and can be run standalone with parry serve --idle-timeout 1800. Hook calls auto-start it if not running.

Scan results are cached in ~/.parry/scan-cache.redb (30-day TTL, ~8ms cache hits vs ~70ms+ inference). Cache is shared across projects and pruned hourly.

Detection Layers

Multi-stage, fail-closed (if unsure, treat as unsafe):

1. Unicode — invisible characters (PUA, unassigned codepoints), homoglyphs, RTL overrides
2. Substring — Aho-Corasick matching for known injection phrases
3. Secrets — 40+ regex patterns for credentials (AWS, GitHub/GitLab, cloud providers, database URIs, private keys, etc.)
4. ML Classification — DeBERTa v3 transformer with text chunking (256 chars, 25 overlap) and head+tail strategy for long texts. Configurable threshold (default 0.7).
5. Bash Exfiltration — tree-sitter AST analysis for data exfil: network sinks, command substitution, obfuscation (base64, hex, ROT13), DNS tunneling, cloud storage, 60+ sensitive paths, 40+ exfil domains
6. Script Exfiltration — same source→sink analysis for script files across 16 languages

Scan modes

Use fast for interactive workflows; full for high-security or batch scanning (parry diff --full). The two models cover different blind spots — DeBERTa v3 catches common injection patterns while Llama Prompt Guard 2 is better at subtle, context-dependent attacks (role-play jailbreaks, indirect injections). Running both as an OR ensemble reduces missed attacks at ~20x higher latency per chunk.

Config

Global flags

Subcommand flags

Env-only

Custom patterns: ~/.config/parry/patterns.toml (add/remove sensitive paths, exfil domains, secret patterns). Custom models: ~/.config/parry/models.toml (used with --scan-mode custom, see examples/models.toml).

ML Backends

One backend is always required (enforced at compile time). Nix builds candle by default.

# Build with ONNX instead of candle
cargo build --no-default-features --features onnx-fetch

Performance

Apple Silicon, release build, fast mode (DeBERTa v3 only). ONNX is 5-7x faster than Candle. Run just bench-candle / just bench-onnx to reproduce (requires HF_TOKEN).

Llama Prompt Guard 2 (~1.5s/chunk) does not ship an ONNX export, so full mode uses Candle for PG2 regardless of backend.

Development

nix develop              # enter dev shell with all tools (rust, just, taplo, typos, actionlint)

just check               # run all checks (clippy, test, fmt, lint, typos, audit)
just build               # build workspace (candle)
just build-onnx          # build workspace (onnx-fetch)
just test                # run tests
just e2e            # run ML e2e tests (requires HF_TOKEN, see below)
just bench-candle        # benchmark ML inference, candle backend (requires HF_TOKEN)
just bench-onnx          # benchmark ML inference, ONNX backend (requires HF_TOKEN)
just clippy              # lint
just fmt                 # format all (rust + toml)
just setup-hooks         # configure git hooks

ML end-to-end tests

The ML e2e tests are #[ignore]d by default since they require a HuggingFace token and model downloads. To run them:

HF_TOKEN=hf_... just e2e

This tests both fast (DeBERTa only) and full (DeBERTa + Llama PG2) modes with semantic injection prompts and clean text. First run downloads models (~100MB each).

Credits

• ML model: ProtectAI/deberta-v3-small-prompt-injection-v2
  • Same model used by LLM Guard
• Exfil patterns: Inspired by GuardDog (Datadog's malicious package scanner)
• Full scan mode optionally uses Llama Prompt Guard 2 86M by Meta, licensed under the Llama 4 Community License. Built with Llama.

License

MIT

Llama Prompt Guard 2 (used in full scan mode) is licensed separately under the Llama 4 Community License. See LICENSE-LLAMA.