Sentinel - The MCP Interceptor

A transparent, fail-open observability sidecar for Model Context Protocol (MCP).
Sentinel provides identity, ordering, and integrity guarantees for agent ↔ tool interactions - without modifying execution or coupling to agents.

Sentinel sits invisibly between an LLM client and its MCP tools, acting as a passive, non-blocking tap into live agent traffic. It does not alter requests. It does not gate execution. It does not impose policy.

Instead, Sentinel observes MCP traffic as it flows, reconstructs a canonical event stream, and exposes it to real-time visualization and durable audit logs.

The result:
You can finally see what your agent did, in what order, and trust the record afterward - even when the agent itself is a black box.

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🚀 Try It Now (30 seconds)

# 1. Install Sentinel
curl -fsSL https://raw.githubusercontent.com/EngramAI-io/sentinel/main/install.sh | sh

# 2. Run Sentinel in front of any MCP server
 sentinel run -- 

# For example:
node mcp_client.js sentinel run --audit-log test_audit.jsonl -- node mcp_server.js

# 3. Open the dashboard
# http://localhost:3000

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⚠️ Project Status
Sentinel is under active development. Core architecture and guarantees are implemented, with ongoing work on hardening, UX polish, documentation, and extended verification tooling.
Early adopters and reviewers are encouraged to provide feedback.

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What Sentinel Is (and Is Not)

Sentinel is:

• A transparent MCP sidecar
• A canonical event recorder
• A real-time observability layer
• A cryptographically verifiable audit tap

Sentinel is not:

• An execution engine
• A policy enforcer
• A tool broker
• A rate limiter
• A replay controller

Agents and tools continue to function exactly the same with or without Sentinel.

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Sentinel vs Official MCP Inspector

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Why Sentinel Exists

LLM agents reason implicitly.
Tool calls happen asynchronously.
Failures often appear after the cause.

Traditional logging breaks down.

Sentinel exists to provide observability guarantees that agent systems implicitly rely on but rarely formalize.

With Sentinel, you get:

• A single, ordered history of agent activity
• Request → response correlation across tools
• Latency and error visibility by method