Pincer

Pincer MCP 🦀

[Pincer-MCP]

[License] [TypeScript] [MCP] [NPM Version] [NPM Downloads] [MCP Registry]

Pincer-MCP is a security-hardened Model Context Protocol (MCP) gateway that eliminates the "Lethal Trifecta" vulnerability in agentic AI systems. By acting as a stateless intermediary, Pincer ensures agents never see your real API keys.

🔒 The Problem

Current AI agents store long-lived API keys in plain-text .env files or local databases. If compromised via prompt injection or host intrusion, attackers gain direct access to your:

• Database passwords
• Third-party API keys

✨ The Solution: Proxy Token Architecture

Pincer implements a "blindfold" security model:

1. Agent knows: Only a unique proxy token (pxr_abc123...)
2. Pincer knows: Mapping of proxy tokens → real API keys (encrypted in OS keychain)
3. Agent never sees: The actual credentials

sequenceDiagram    participant Agent    participant Pincer    participant Vault (OS Keychain)    participant External API
    Agent->>Pincer: tools/call + proxy_token: pxr_abc123    Pincer->>Vault: Decrypt real API key    Vault-->>Pincer: gemini_api_key: AIzaSy...    Pincer->>External API: API call with real key    External API-->>Pincer: Response    Pincer->>Pincer: Scrub key from memory    Pincer-->>Agent: Response (no credentials)

📦 Available Tools

• gemini_generate: Secure Google Gemini API calls.
• openai_chat: Chat completions with OpenAI GPT models (gpt-4o, gpt-4-turbo, gpt-3.5-turbo, etc.).
• openai_list_models: List all available OpenAI models.
• openai_compatible_chat: Chat completions with any OpenAI-compatible API (Azure OpenAI, Ollama, vLLM, etc.).
• openai_compatible_list_models: List models from custom OpenAI-compatible endpoints.
• claude_chat: Chat completions with Anthropic Claude models (Claude 3.5 Sonnet, Opus, Haiku).
• openrouter_chat: Unified API access to 100+ models from multiple providers (OpenAI, Anthropic, Google, Meta, etc.).
• openrouter_list_models: List all available models across OpenRouter providers.
• openwebui_chat: OpenAI-compatible interface for self-hosted LLMs.
• openwebui_list_models: Discover available models on an OpenWebUI instance.
• gpg_sign_data: Sign data or files using a GPG/PGP private key stored in Pincer's vault. (Keyless Execution — agent never sees the key)
• gpg_decrypt: Decrypt PGP-encrypted data using a vault-stored private key.

🔑 GPG Key Management

# Generate a new GPG keypair (private key stored in vault)pincer key generate --name "Release Signing" --email [email protected]
# Import an existing PGP private keypincer key import ./my-key.asc --passphrase "my-passphrase"
# List all stored GPG keyspincer key list
# Export public key (safe to share)pincer key export <key-id>
# Authorize an agent for signingpincer agent authorize mybot gpg_sign_data --key <key-id>

(More callers coming soon!)

🚀 Quick Start

Prerequisites

• Node.js 18+
• macOS, Windows, or Linux with native keychain support

Installation

Option 1: Global Installation (Recommended)

npm install -g pincer-mcp# Now 'pincer' command is available system-wide

Option 2: Local Development

git clone https://github.com/VouchlyAI/Pincer-MCP.gitcd Pincer-MCPnpm installnpm run buildnpm link  # Makes 'pincer' command available locally

Setup Vault

# 1. Initialize vault (creates master key in OS keychain)pincer init
# 2. Store your real API keys (encrypted)pincer set gemini_api_key "AIzaSyDpxPq..."pincer set openai_api_key "sk-proj-..."
# 3. Register an agent and generate proxy tokenpincer agent add openclaw# Output: 🎫 Proxy Token: pxr_V1StGXR8_Z5jdHi6B-myT
# 4. Authorize the agent for specific toolspincer agent authorize openclaw gemini_generate

Multi-Key Support

Store multiple keys for the same tool and assign them to different agents:

# Store two different Gemini API keyspincer set gemini_api_key "AIzaSy_KEY_FOR_CLAWDBOT..." --label key1pincer set gemini_api_key "AIzaSy_KEY_FOR_MYBOT..." --label key2
# View all stored keyspincer list
# Assign specific keys to each agentpincer agent add clawdbotpincer agent authorize clawdbot gemini_generate --key key1
pincer agent add mybot  pincer agent authorize mybot gemini_generate --key key2
# View agent permissionspincer agent list

Result: clawdbot uses key1, mybot uses key2 - perfect for rate limiting or cost tracking!

Run the Server

npm run dev

Configure Your Agent

Give your agent the proxy token (not the real API key):

export PINCER_PROXY_TOKEN="pxr_V1StGXR8_Z5jdHi6B-myT"

Tool-to-Secret Name Mappings

When storing secrets, you must use the correct secret name for each tool. See the Tool Mappings Guide for a complete reference.

When you run pincer agent authorize myagent gemini_generate, Pincer will inject the gemini_api_key secret when that tool is called.

Make a Tool Call

Your agent sends requests with the proxy token in the body:

{  "jsonrpc": "2.0",  "method": "tools/call",  "params": {    "name": "gemini_generate",    "arguments": {      "prompt": "Hello world",      "model": "gemini-2.0-flash"    },    "_meta": {      "pincer_token": "pxr_V1StGXR8_Z5jdHi6B-myT"    }  }}

Pincer maps the proxy token to the real API key and executes the call securely.

🏗️ Architecture

Two-Tiered Vault System

Tier 1: Master Key (OS Keychain)

• Stored in macOS Keychain, Windows Credential Manager, or GNOME Keyring
• Never touches the filesystem
• Accessed only for encryption/decryption

Tier 2: Encrypted Store (SQLite)

• Database at ~/.pincer/vault.db
• Three tables:
  • secrets: Real API keys (AES-256-GCM encrypted)
  • proxy_tokens: Proxy token → Agent ID mappings
  • agent_mappings: Agent ID → Tool authorization

Authentication Flow

Request (_meta.pincer_token: pxr_xxx)  ↓Gatekeeper: Extract proxy token from body  ↓Vault: Resolve pxr_xxx → agent_id → tool_name → real_api_key  ↓Injector: JIT decrypt & inject real key  ↓Caller: Execute external API call  ↓Scrubber: Overwrite key in memory with zeros  ↓Audit: Log to tamper-evident chain

🔐 Security & Compliance

Pincer is built for enterprise-grade security:

• Hardware-Backed Cryptography: Master encryption keys never leave the OS-native keychain.
• Proxy Token Isolation: Agents only handle ephemeral pxr_ tokens; they never touch real credentials.
• JIT Decryption: Secrets are decrypted only for the duration of the API call.
• Zero-Footprint Memory: Sensitive data is scrubbed (zeroed out) from memory immediately after use.
• Fine-Grained Authorization: Strict per-agent, per-tool access control policies.
• Tamper-Evident Audit Log: Append-only tool call history with SHA-256 chain-hashing.
• Hardened Execution: Schema validation on all inputs and protected environment execution.
• Stdio Compatible: Fully compatible with the standard Model Context Protocol transport.

🔍 Audit Logs

Every tool call is logged to ~/.pincer/audit.jsonl with both UTC and Local timestamps, plus character counts and estimated token usage:

{  "agentId": "openclaw",  "tool": "gemini_generate",  "duration": 234,  "status": "success",  "input_chars": 156,  "output_chars": 423,  "estimated_input_tokens": 39,  "estimated_output_tokens": 106,  "timestamp_utc": "2026-02-05T08:32:00.000Z",  "timestamp_local": "2/5/2026, 2:02:45 PM",  "chainHash": "a1b2c3d4e5f6g7h8",  "prevHash": "0000000000000000"}

Token Estimation: Pincer automatically estimates token usage using a 4:1 character-to-token ratio (~4 characters per token average). This provides consistent cost tracking across all AI providers without relying on provider-specific APIs.

Chain hashes provide tamper detection - any modification breaks the SHA-256 chain.
## 🧪 Development
```bash# Install dependenciesnpm install
# Run testsnpm test
# Run with watch modenpm run dev
# Build for productionnpm run build

📚 Documentation

• Setup Guide - Getting started with Pincer-MCP
• IDE Integration - Use Pincer with VSCode, Claude Desktop, Cursor, and more
• OpenClaw Integration - Integrate Pincer with OpenClaw agents
• Testing Guide - Comprehensive test suite documentation
• Capabilities Reference - Full API and feature documentation
• Security Policy - Vulnerability reporting and security best practices
• CHANGELOG - Version history and release notes

🤝 Contributing

Contributions are welcome! Please see CONTRIBUTING.md for guidelines.

📄 License

BSL 1.1 (Business Source License) — See LICENSE for details. Converts to Apache 2.0 on 2028-04-01.

• Model Context Protocol - The standard for AI tool integration.
• keytar - Secure cross-platform keychain access.
• better-sqlite3 - High-performance local persistence.

Built with ❤️ for a more secure AI future.