ProtoMCP

Postman for MCP servers — connect, explore, and test from your browser

Live Demo  ·  Docs  ·  Get Started

ProtoMCP is a browser-based inspector for MCP servers. Point it at any MCP server — local or remote — and you get a full UI to browse tools, prompts, and resources, fire requests, and watch every JSON-RPC exchange in real time.

Why ProtoMCP?

• Browser-only — No native app, no extensions, no localhost stdio gaps
• Multi-server — Connect 13+ public MCP servers in a single workspace
• Real-time trace — Watch every JSON-RPC exchange live (Claude Desktop doesn't show this)
• Zero-config introspection — Auto-discovers tools, prompts, resources from schemas

How It Compares

What it does

Explore Mode

Connects to any MCP server over Streamable HTTP or SSE. Once connected, ProtoMCP discovers all capabilities automatically and generates input forms from the server's JSON Schema — so you can invoke tools, preview prompts, and browse resources without writing a single line of code. Every request and response is logged with timing data in a live panel alongside.

Agent Mode

Drops an AI assistant on top of your connected servers. Pick a provider (OpenAI, Anthropic, Gemini, Groq, or others), write a prompt, and watch the agent reason and call tools across all connected servers in real time. You can require confirmation before each tool call if you want to stay in the loop — useful when the tools have side effects.

Multiple servers can be connected at the same time. Tools and resources from all of them are aggregated into a single workspace, so you can mix and match across servers in a single agent session.

Get Started

Hosted — no setup, open in your browser:

https://protomcp.io/

Run locally:

pip install jaclang==0.12.0 jac-client==1.0.7 byllm jac-mcp jasketch-mcp-server
git clone https://github.com/SahanUday/ProtoMCP.git && cd ProtoMCP
jac start main.jac

Open http://localhost:8000. To connect a local MCP server, see the ngrok tunnel guide.

Featured Servers

Built-in servers (no URL required):

• jac-mcp — Jac language validation, formatting, and docs
• jasketch — Live diagram canvas

View all 13+ servers →

Transport Support

Authentication

Architecture

graph TB
    User(["User"])

    subgraph Browser["Browser"]
        UI["Explore / Agent UI"]
    end

    subgraph Backend["Jac Backend"]
        Proxy["CORS Proxy"]
        Agent["Agent Runner"]
    end

    subgraph External["External Services"]
        MCP["MCP Servers"]
        LLM["LLM Providers"]
    end

    User --> UI
    UI -->|"agent requests"| Agent
    Proxy <-->|"JSON-RPC"| MCP
    Agent <-->|"tool use"| Proxy
    Agent <-->|"chat"| LLM
    Agent -->|"streaming trace"| UI

The Jac backend bypasses browser CORS restrictions by proxying all MCP requests. It pools SSE connections for legacy servers and runs the ReAct loop for Agent Mode, streaming the full trace back to the client in real time.

Tech Stack

Configuration

Environment Variables

Session Storage

• mcp_saved_connections — Connection configs (URL, auth, transport)
• mcp_agent_session_history — Agent chat sessions (max 5)

Roadmap

• Desktop App — Native app via Tauri with direct localhost and stdio transport support. See the Desktop App docs.

Development

# Install dependencies
pip install jaclang jac-client byllm jac-mcp jasketch-mcp-server

# Start dev server
jac start main.jac

# Run with hot reload (file watching)
pip install watchdog
jac start main.jac --watch

Adding a New Server to Registry

Edit data/mcp_servers.cl.jac:

{
    "id": "your-server",
    "name": "Your Server",
    "namespace": "example.com",
    "transport": "http",  # or "sse"
    "description": "Single-line description",
    "url": "https://example.com/mcp",
    "auth": "bearer",  # or "apikey", "basic", "none"
    "authRequired": True
}

Contributing

Issues and pull requests are welcome. If you're fixing a bug, open a PR directly. If you're adding something new, open an issue first so we can align on the approach before you build it.

Check open issues for things tagged good first issue or help wanted.

License

MIT — see LICENSE for details.