@sentinel-core/mcp

MCP server that exposes sentinel's runtime data — API calls, Redux state, action log, value lineage — to MCP-speaking coding agents (Claude Code, Cursor, …). The agent that writes your code can also see your running page.

Browser (sentinel) ──WebSocket──▶ sentinel-mcp process ──stdio──▶ Claude Code
   effects, state,                  pulls a fresh snapshot
   actionLog, lineage               per tool call

Setup

1. Register the server with your agent:

claude mcp add sentinel -- npx @sentinel-core/mcp

2. Enable the bridge in your app (requires @sentinel-core/sentinel ≥ 1.0.61):

import { SentinelProvider } from "@sentinel-core/sentinel";

<SentinelProvider store={store} sagaMonitor={monitor} mcp={{ url: "ws://localhost:8790" }}>
  <App />
</SentinelProvider>

The bridge connects to the MCP process over WebSocket, reconnects silently with backoff, and answers snapshot requests on demand. No mcp prop → no bridge, zero impact.

3. Open your app locally, start a new agent session and ask: "where does this price value come from?"

productState.product.prices[0].value = 1299
  ← GET_PRODUCT_FULFILLED (client, 14:02:31)
  ← GET https://…/productDetail (200, 340ms, client)

Tools

| Tool | Answers | |---|---| | get_lineage(query, tab_id?) | Where does this value come from? Query matches state paths ("price") and values ("1299"); returns state path ← redux action ← API request chains | | list_api_calls(tab_id?) | Every request the page made (SSR + client) with method, URL, status, duration, origin | | get_duplicates(tab_id?) | Requests issued more than once, incl. server+client double-fetches | | get_state(path?, query?, tab_id?) | Exact value at a path, free-text search, or top-level summary | | get_action_log(limit?, tab_id?) | Recent redux actions with deep-diff paths of what they changed | | get_component_props(name?, tab_id?) | Props a React component actually received. name lists every instance of that component with its current props + render count; omit name to list all captured components. Sees props that never touch redux (local/computed/context) | | list_tabs() | Connected browser tabs; the last active tab is the default target |

All tools accept an optional tab_id (from list_tabs); without it the last active tab is used.

Configuration

| | | |---|---| | Port | 8790 by default — override with SENTINEL_MCP_PORT | | Binding | 127.0.0.1 only — snapshots never leave your machine | | Snapshot timeout | 3s per tool call; clear error message when no tab is connected |

How it works

The process holds no state: each tool call pulls a fresh snapshot (Redux state, serialized saga effects, action log — both SSR and client origin) from the active browser tab, then runs sentinel's deterministic analysis functions (buildLineageFromQuery, extractApiCalls, …) on it. No AI calls, no API keys, everything local.

License

MIT