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How to Connect Claude Desktop to Rockxy's MCP Server (3-Minute Setup)

· 6 min read

Rockxy 0.9.0 ships with a built-in Model Context Protocol (MCP) server. Once connected, Claude Desktop can read your captured HTTP flows, replay requests, and diff two responses — without you pasting curl output into a chat window. This guide walks through the three-minute setup and shows you what Claude can actually do with your traffic.

Why connect Claude Desktop to your HTTP traffic

HTTP debugging has always been a copy-paste problem. You see a failing request in a proxy, you copy the headers and body, you paste them into a chat or a doc, and you write a human-readable question around them. Context switching eats time. And the assistant on the other end only sees what you thought to paste.

MCP flips that. Instead of pasting, you give Claude a direct channel to your proxy. Claude calls list_flows, reads the ones it needs, and asks follow-up questions with the actual bytes in front of it. The failing request is no longer a screenshot — it's a tool call the model can re-run after it proposes a fix.

Once you connect the two, your debugging loop compresses. You describe what you're seeing in plain English. Claude reads the actual request, not a paraphrased version of it. When Claude proposes a fix, it can test the fix by replaying the modified request right there. The assistant and the proxy are on the same page, and that page is your terminal — nothing leaves your Mac.

Prerequisites

  • macOS 14 (Sonoma) or later. Rockxy's MCP binary is a universal build (Apple Silicon + Intel).
  • Claude Desktop installed with a recent version that supports MCP (any build from late 2024 onward).
  • Rockxy 0.9.0 or later. Earlier builds do not ship the MCP server.
  • Five minutes of quiet. The actual work takes three, but leave room for a Gatekeeper prompt on first launch.

Step 1: Install Rockxy

Download the DMG from rockxy.io/download, mount it, and drag Rockxy.app into /Applications. Launch it once so macOS records the app as trusted.

The first launch will show a Gatekeeper prompt — Rockxy is signed and notarized, so the dialog should say "Rockxy" can be opened. If you see a scarier "cannot be verified" dialog, open System Settings → Privacy & Security, scroll to the Security section, and click Open Anyway.

Once Rockxy is running, the MCP binary lives at:

/Applications/Rockxy.app/Contents/MacOS/rockxy-mcp

You will reference this exact path in Step 3. Keep it handy.

Step 2: Enable the MCP server in Rockxy

Open Rockxy → Settings → MCP (or press Cmd+, and click the MCP tab). Toggle Enable MCP Server on.

Rockxy's MCP server runs as an on-demand child process spawned by the MCP client. It communicates with Claude Desktop over stdio — standard input and standard output — so the MCP transport itself is not a network socket. Rockxy also binds an optional local HTTP port on loopback for non-stdio clients; both paths stay on your Mac.

When MCP is enabled, Rockxy exposes four tools: list_flows, get_flow_detail, replay_request, and diff_flows. Each is scoped to the currently open session file, so you choose what Claude can see by choosing which session is open.

A quick note on each tool. list_flows takes optional filters — host, method, status, a time window, a result limit — and returns an array of flow summaries. get_flow_detail takes a single flow id and returns the full request (headers, body), full response (headers, body), and the timing breakdown (DNS, TCP, TLS, TTFB, transfer). replay_request takes a flow id and an optional overrides object, re-executes the request against the original host, and returns the new flow id. diff_flows takes two flow ids and returns a structural diff — path, headers, body fields — so Claude can summarize what changed without eyeballing two JSON blobs.

Step 3: Edit claude_desktop_config.json

Claude Desktop reads its MCP configuration from a single JSON file:

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

If the file does not exist yet, create it. If it exists with other MCP servers, add the Rockxy block to the existing mcpServers object. A fresh file that wires up only Rockxy looks like this:

{
  "mcpServers": {
    "rockxy": {
      "command": "/Applications/Rockxy.app/Contents/MacOS/rockxy-mcp",
      "args": []
    }
  }
}

Save the file. No reloads required yet — Claude Desktop only reads the config at startup.

Step 4: Restart Claude Desktop

Fully quit Claude Desktop with Cmd+Q. Closing the window is not enough — the app keeps running in the background, and a background process will not re-read the config. Reopen it from Launchpad or Spotlight.

When Claude Desktop starts, it spawns the Rockxy MCP process as a child, connects over stdio, and reads the tool manifest. You will see a small plug icon in the Claude Desktop chat interface indicating that an MCP server is attached.

Step 5: Verify the connection

Start a new chat in Claude Desktop and send:

List the last 5 HTTP flows captured by Rockxy.

Expected behavior: Claude calls the list_flows tool with limit=5. You will see a tool-use block in the chat — usually collapsed — containing the raw input and output. Claude then summarizes the flows in plain text: method, host, path, status, size.

If the list is empty, generate some traffic first. Turn on Rockxy's system proxy, open a browser tab, and reload. Then ask Claude the same question again.

Troubleshooting

Binary not found. If Claude Desktop logs command not found or the MCP plug never lights up, re-check the path in the config. The correct path is always /Applications/Rockxy.app/Contents/MacOS/rockxy-mcp — if you moved Rockxy to ~/Applications, adjust accordingly.

MCP not enabled in Rockxy. The MCP server will accept stdio and respond with a mcp_disabled error if you never toggled it on in Settings. Flip the switch, then restart Claude Desktop.

Claude cannot see the tools. If the plug icon is present but Claude says "I don't have that tool," check the Claude Desktop developer console (Cmd+Option+I on recent builds). A JSON parse error in claude_desktop_config.json is the usual cause — a missing comma, a stray trailing comma, or smart quotes pasted from a word processor.

What Claude can do with your traffic

Once connected, try prompts like these:

  • "Why did my last request to /api/auth fail?" — Claude calls list_flows, filters by host and path, grabs the detail of the 401, reads the WWW-Authenticate header, and explains.
  • "Diff the two most recent GraphQL mutations." — Claude lists flows, picks the two mutations, calls diff_flows, and summarizes which fields changed.
  • "Replay flow 42 but with an Authorization header of Bearer eyJ...." — Claude calls replay_request with the override, reads the new response, and tells you whether it is still 401.
  • "Which endpoints are slowest in this session?" — Claude walks the flow list, pulls timing data from each detail, and ranks them.

The MCP server is a small tool surface — four functions — which is intentional. Narrow surfaces are easier for the model to reason about, and they keep your traffic bounded to the operations you explicitly approved.

One behavior worth knowing: every tool call shows up as a collapsible block in the Claude Desktop chat. You can expand any block to see the exact input the model sent and the exact output the tool returned. If you ever wonder whether Claude is doing what you asked, that collapsible is the answer. It's also how you debug prompts that go sideways — you can see whether the model filtered list_flows by the right host, or whether it passed a wrong flow id into get_flow_detail.

Next steps

Now that the plumbing is connected, the interesting work is in the prompts. The Stripe webhook case study walks through a real debugging session end to end. The MCP section on the homepage has the current tool reference.

Rockxy is free and open source under AGPL-3.0. The MCP server's source lives in the same repository as the rest of the app — you can read exactly what it exposes before you wire it into any assistant.

Download Rockxy See MCP tools