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MCP Quickstart

Use Rhumb through the Model Context Protocol — the fastest path to agent tool discovery and execution.

Default path

For most agents, the default production path is:

  1. discover a Service or Capability
  2. resolve ranked providers, or follow the machine-readable recovery handoff
  3. estimate the call
  4. execute through Layer 2 with RHUMB_API_KEY

Use x402 only when zero-signup per-call payment is the point. For repeat traffic, use governed API key or wallet-prefund on X-Rhumb-Key, and bring BYOK or Agent Vault only when provider control is the point.

Install

npx rhumb-mcp@latest

Zero config. Discovery tools work immediately.

Add to Claude Desktop

Add to your claude_desktop_config.json:

{
  "mcpServers": {
    "rhumb": {
      "command": "npx",
      "args": ["rhumb-mcp@latest"],
      "env": {
        "RHUMB_API_KEY": "your_key_here"
      }
    }
  }
}

The governed API key is optional — discovery tools work without it. Add it to enable execution.

Add to Cursor

In Cursor settings → MCP Servers → Add:

{
  "rhumb": {
    "command": "npx",
    "args": ["rhumb-mcp@latest"],
    "env": {
      "RHUMB_API_KEY": "your_key_here"
    }
  }
}

What you can do

Without a governed API key (free, no signup)

  • find_services — "Find the best email API for agents"
  • get_score — "What's Stripe's agent-native score?"
  • get_alternatives — "What are alternatives to SendGrid?"
  • get_failure_modes — "What breaks when agents use HubSpot?"
  • discover_capabilities — "What capabilities exist for payments?"

With a governed API key (default production path)

  • resolve_capability — "Which provider or recovery handoff should I use for email.send, and what if I only want BYOK or Rhumb-managed?"
  • estimate_capability — "What execution rail, health, and cost should I expect before this call runs?"
  • execute_capability — "Send an email through the best provider"
  • get_receipt — "Show me the receipt for that execution"
  • usage_telemetry — "How are my calls performing this week?"
  • budget / spend — "Set a $10/day budget"

Minimal recommended flow

  1. discover_capabilities — find the action you want
  2. resolve_capability — see ranked providers, optional credential-mode filters, machine-readable recovery fields like recovery_hint.resolve_url, recovery_hint.credential_modes_url, and, when applicable, recovery_hint.alternate_execute_hint or recovery_hint.setup_handoff, plus search suggestions when the capability ID is wrong
  3. estimate_capability — check the active execution rail, health, and cost before execution
  4. execute_capability — run the action

If you ask for a specific mode such as byok or rhumb_managed and nothing is execute-ready, resolve_capability can still return the next action as machine-readable recovery_hint.alternate_execute_hint or recovery_hint.setup_handoff instead of leaving you to rediscover it manually. If you typo the capability ID, it can also return a capability search URL plus suggested capabilities instead of a blank dead end.

Get a governed API key

  1. Go to rhumb.dev/auth/login
  2. Sign in with GitHub or Google
  3. Copy your governed API key from the dashboard

Example conversation

You: Find me the best API for sending transactional emails from an AI agent.

Agent (using find_services): Found 8 email services. Top 3 by AN Score:

  • Resend: 7.8 (L3 Ready) — cleanest API, best agent ergonomics
  • Postmark: 6.8 (L3 Ready) — reliable delivery, some signup friction
  • SendGrid: 5.5 (L2 Developing) — powerful but complex auth model

You: What are Resend's failure modes?

Agent (using get_failure_modes): 3 known failure modes for Resend:

  • Domain verification required before sending (blocks cold start)
  • Rate limit headers not always present
  • Webhook signatures use asymmetric keys (unusual pattern)

You: Ok, send a test email through Resend.

Agent (using execute_capability): Executing email.send via Resend...

  • Cost estimate: $0.001
  • Status: 200 OK
  • Message ID: msg_abc123

Notes

  • Discovery works with no key.
  • Execution through governed API key or wallet-prefund uses RHUMB_API_KEY (your governed API key).
  • Use x402 through the REST API when zero-signup per-call payment matters (no RHUMB_API_KEY required).
  • Use wallet-prefund when the same wallet needs repeat traffic.