receipts-mcp 0.1.2

MCP proxy that records and cryptographically signs AI agent tool calls

Receipts MCP Proxy

receipts_mcp/ is a stdio MCP server that sits between an MCP client and one or more upstream MCP servers.

For each tool call:

1. The client calls the Receipts proxy.
2. The proxy forwards the call to the real upstream MCP server.
3. The real output is captured.
4. The proxy POSTs that result to POST /tools/record on the Receipts backend.
5. The real result is returned to the client even if receipting fails.

Upstream tools are namespaced as <server>__<tool> so collisions do not clobber each other.

If no upstream config file exists, the proxy falls back to the built-in demo tools:

• write_file
• http_fetch
• db_query

Those demo tools are forwarded to the backend's /tools/call endpoint.

Setup

pip install receipts-mcp
cp upstreams.json.example upstreams.json

Configuration

receipts_mcp/config.py reads environment variables and an upstreams JSON file.

Environment variables:

Variable	Default	Purpose
RECEIPTS_URL	http://localhost:8000	Receipts backend URL
RECEIPTS_API_KEY	empty	Proxy-role API key used for /tools/record
UPSTREAMS_PATH	receipts_mcp/upstreams.json	Path to upstream config
TOOL_TIMEOUT_SECONDS	60	Max time for an upstream tool call
RECORD_TIMEOUT_SECONDS	5	Max time for backend receipting

The upstreams file supports:

• stdio
• sse
• streamable_http

${ENV_VAR} references inside env and headers are expanded from the process environment.

Example:

{
  "include_demo_tools": false,
  "upstreams": {
    "github": {
      "transport": "stdio",
      "command": "/path/to/github-mcp",
      "args": [],
      "env": {
        "GITHUB_TOKEN": "${GITHUB_TOKEN}"
      }
    }
  }
}

Claude Code / Cursor config

Add this to ~/.claude/claude_mcp_config.json or the equivalent Cursor MCP config:

{
  "mcpServers": {
    "receipts": {
      "command": "/home/shreyansh/receipts/.venv/bin/python3",
      "args": ["-m", "receipts_mcp.server"],
      "cwd": "/home/shreyansh/receipts",
      "env": {
        "RECEIPTS_URL": "http://localhost:8000",
        "RECEIPTS_API_KEY": "<proxy-key>",
        "UPSTREAMS_PATH": "receipts_mcp/upstreams.json",
        "PYTHONPATH": "/home/shreyansh/receipts"
      }
    }
  }
}

Restart the MCP client after changing the config.

Runtime behavior

• One proxy process gets one mcp-<hex> session ID.
• All tool calls from that process share that session so they can be reconciled together.
• If the backend is unreachable, the tool result still returns and the receipt is skipped.
• If the backend rejects the API key, the proxy logs it as a configuration error.

Run

python3 -m receipts_mcp

or

python3 -m receipts_mcp.server