nats-mcp

MCP server for NATS — publish messages, request-reply, manage JetStream streams, use the KV store, and inspect server diagnostics over stdio.

Installation

npx -y @daanrongen/nats-mcp

Tools (17 total)

| Domain | Tools | Coverage | | ----------- | ----------------------------------------------------------------------------------------------------------------------- | ----------------------------------------------- | | Core | publish, request | Publish messages, request-reply pattern | | Streams | stream_list, stream_info, stream_create, stream_delete, stream_publish, stream_fetch, stream_consumer_create | JetStream stream lifecycle and message delivery | | KV | kv_create_bucket, kv_list_buckets, kv_get, kv_put, kv_delete, kv_list_keys, kv_history | Key-value store with history | | Server | server_info | NATS server diagnostics |

Setup

Environment variables

| Variable | Required | Description | | ---------- | -------- | ---------------------------------------- | | NATS_URL | Yes | NATS server URL (e.g. nats://localhost:4222) |

Claude Desktop

Edit ~/Library/Application Support/Claude/claude_desktop_config.json:

{
  "mcpServers": {
    "nats": {
      "type": "stdio",
      "command": "npx",
      "args": ["-y", "@daanrongen/nats-mcp"],
      "env": {
        "NATS_URL": "nats://localhost:4222"
      }
    }
  }
}

Or via the CLI:

claude mcp add nats -e NATS_URL=nats://localhost:4222 -- npx -y @daanrongen/nats-mcp

Development

bun install
bun run dev        # run with --watch
bun test           # run test suite
bun run build      # bundle to dist/main.js
bun run inspect    # open MCP Inspector in browser

Inspecting locally

bun run inspect launches the MCP Inspector against the local build:

bun run build && bun run inspect

This opens the Inspector UI in your browser where you can call any tool interactively and inspect request/response shapes.

Architecture

src/
├── config.ts              # Effect Config — NATS_URL
├── main.ts                # Entry point — ManagedRuntime + StdioServerTransport
├── domain/
│   ├── NatsClient.ts      # Context.Tag service interface
│   ├── errors.ts          # NatsError, KvNotFoundError, StreamNotFoundError
│   └── models.ts          # Schema.Class models (NatsMessage, StreamInfo, KvEntry, …)
├── infra/
│   ├── NatsClientLive.ts  # Layer.scoped — connects via nats.js, drains on shutdown
│   └── NatsClientTest.ts  # In-memory Ref-based test adapter
└── mcp/
    ├── server.ts          # McpServer wired to ManagedRuntime
    ├── utils.ts           # formatSuccess, formatError
    └── tools/             # core.ts, streams.ts, kv.ts, server.ts