Toolplane MCP Inspector

A high-density developer workstation for inspecting, testing, and debugging Model Context Protocol (MCP) servers — live JSON-RPC 2.0 traffic, distributed request traces, OAuth handshakes, tool execution, and call-stack inspection in one place.

Features

• Cluster dashboard — manage multiple MCP server nodes with live health metrics, status, and per-node resource usage.
• Real-time RPC stream — every JSON-RPC 2.0 message is captured (SDK-internal requests included) into a searchable, filterable log with a full payload inspector.
• OAuth & transport trace debugger — step through OAuth client discovery, dynamic client registration, and token exchanges, with pause/resume/terminate control over the handshake.
• Tool playground — call MCP tools with arbitrary JSON arguments and inspect schema-compliant responses with a syntax-highlighted JSON viewer.
• Deep tool analysis — schema parsing/validation, latency percentiles (avg/min/max/P50/P95/P99), and execution history.
• Distributed request tracing — visualize spans/timelines across nodes with status codes and payload drawers.
• Call stack inspector — stack frames plus interactive watch expressions.
• Live SDK connections — connect to real MCP servers over SSE/streamable HTTP via @modelcontextprotocol/sdk, with a dev CORS proxy for servers that reject MCP-specific headers cross-origin.
• Config & persistence — server timeouts, retry limits, log verbosity, environment variables, and a raw localStorage editor. Dark/light/system themes.

Requirements

• Node.js >= 20 (Vite 6 / React 19)

Getting started

Run it without installing (npx)

The package ships a prebuilt client plus a small server that serves it and handles the /mcp-proxy/… CORS proxy, so live connections to real MCP servers work out of the box:

npx toolplane-mcp-inspector

Then open http://localhost:3000 (set PORT to change the port). The app bootstraps a small cluster of simulated MCP servers so every view has data immediately.

Environment variables:

| Variable | Description | | -------------------------- | ------------------------------------------------------------------ | | PORT | Listen port (default 3000) | | HOST | Bind address (default 0.0.0.0) | | MCP_PROXY_ALLOWED_HOSTS | Optional comma-separated allow-list of proxied MCP hosts |

Install locally

npm install toolplane-mcp-inspector
npx toolplane-mcp-inspector

Develop from source

# Install dependencies
npm install

# Start the dev server (http://localhost:3000 by default)
npm run dev

Set PORT to change the port, e.g. PORT=8080 npm run dev.

Connecting to a real MCP server

Use the Connect New… flow and pick an SSE/streamable HTTP transport. The dev server (and the published package's bin/serve.js) proxy same-origin requests under /mcp-proxy/<host>/… so MCP-specific headers (mcp-protocol-version, mcp-session-id, last-event-id) pass through without being blocked by CORS.

Scripts

| Command | Description | | ---------------- | ---------------------------------------- | | npm run dev | Start the Vite dev server | | npm run build | Production build to dist/ | | npm run preview| Preview the production build | | npm run start | Serve the built app (static + /mcp-proxy) | | npm run lint | Type-check with tsc --noEmit | | npm test | Run unit tests (tsx) |

Architecture

The app follows a strict Container / Presentational split around a centralized React context:

• src/services/ — pure logic: JSON-RPC 2.0 construction/parsing, @modelcontextprotocol/sdk clients, OAuth provider, deep tool analysis, and localStorage persistence.
• src/context/McpContext.tsx — global state: navigation, registered servers, RPC logs, traces, stack/watch expressions, config, and background stream tickers.
• src/containers/ — smart components that subscribe to the context and translate state/actions into view props.
• src/views/ + src/components/ — presentational UI (React + Tailwind CSS v4).

Tech stack

React 19 · TypeScript · Vite 6 · Tailwind CSS v4 · @modelcontextprotocol/sdk

Contributing

Contributions are welcome — see CONTRIBUTING.md for setup, test conventions, and the PR process. Please review the Code of Conduct and report security issues per SECURITY.md.

License

MIT · © 2026 Toolplane. Questions? Open an issue.