Monzo MCP Server for Claude Code

Read-only Monzo banking integration for Claude Code. Query balances, view transactions, check pots, and analyze spending — all through natural conversation.

Features

Related MCP server: monarch-mcp

Prerequisites

1. Python 3.10+

2. A Monzo developer OAuth client — confidential type

3. Set the redirect URL to http://localhost:3118/callback

4. Claude Code (CLI or VS Code extension)

Why do I need my own OAuth client? Monzo restricts API access to personal use — there's no public app model. You create your own client at developers.monzo.com and only your credentials touch this server.

Quick Start

1. Create an OAuth Client

Go to developers.monzo.com and create a Confidential client.

• Redirect URL: http://localhost:3118/callback

2. Installation

Option A: Claude Code Plugin (recommended)

Gives you the MCP server plus domain knowledge skills, auth hooks, and auto-updates.

In a Claude Code session, run:

/plugin marketplace add tcoretech/monzo-mcp
/plugin install monzo@tcoretech-monzo-mcp
/reload-plugins
/plugin enable monzo

Then "Configure Options" to set MONZO_CLIENT_ID and MONZO_CLIENT_SECRET (stored in the system keychain).

Option B: Claude Code MCP (server only)

uvx (no install needed):

claude mcp add monzo \
  -e MONZO_CLIENT_ID=your_client_id \
  -e MONZO_CLIENT_SECRET=your_client_secret \
  -- uvx --from monzo-mcp monzo-mcp

pip install:

pip install monzo-mcp
claude mcp add monzo \
  -e MONZO_CLIENT_ID=your_client_id \
  -e MONZO_CLIENT_SECRET=your_client_secret \
  -- monzo-mcp

From source:

git clone https://github.com/tcoretech/monzo-mcp.git
cd monzo-mcp
pip install -e .
claude mcp add monzo \
  -e MONZO_CLIENT_ID=your_client_id \
  -e MONZO_CLIENT_SECRET=your_client_secret \
  -- python3 mcp-server/server.py

Option C: Any MCP Client (JSON config)

For Claude Desktop, Cursor, or any other MCP-compatible client, add this to your configuration:

{
  "mcpServers": {
    "monzo": {
      "command": "uvx",
      "args": ["--from", "monzo-mcp", "monzo-mcp"],
      "env": {
        "MONZO_CLIENT_ID": "YOUR_CLIENT_ID",
        "MONZO_CLIENT_SECRET": "YOUR_CLIENT_SECRET"
      }
    }
  }
}

Authentication (Seamless OAuth)

This server implements a Seamless Loopback Flow. You don't need to run a separate setup command.

1. Just-in-Time Auth: When you first ask Claude about your Monzo account, the server will detect missing tokens and automatically open your browser to the Monzo login page.

2. Loopback Listener: A temporary local server (defaulting to port 3118) catches the callback from Monzo and saves your tokens securely to the system keychain.

3. WSL & Docker Support: The server is environment-aware and will use PowerShell to bridge to your Windows host browser if running in WSL.

4. SCA (Strong Customer Authentication): If Monzo requires an app approval, Claude will inform you. Simply tap "Approve" in your Monzo mobile app and tell Claude you've done so.

Note: Tokens are stored in the system keychain when available, with a plaintext fallback at ~/.monzo-mcp/tokens.json (0600 permissions). Existing plaintext tokens are automatically migrated to the keychain. Access tokens are refreshed automatically.

Where are tokens stored?

To force re-authentication, clear the keychain entry or delete the fallback file.

Usage Examples

Once connected, ask Claude things like:

• "What's my Monzo balance?"

• "Show my last 20 transactions"

• "How much did I spend on eating out this month?"

• "Give me a spending summary for the last 30 days"

• "What are my pot balances?"

• "Show transactions from Tesco last week"

Architecture

monzo-mcp/
├── .claude-plugin/          # Plugin metadata
│   ├── plugin.json
│   ├── marketplace.json
│   └── hooks/
│       ├── hooks.json       # Session-start auth check hook
│       └── check-monzo-auth.sh
├── mcp-server/              # MCP server (Python)
│   ├── server.py            # FastMCP entry point (stdio)
│   ├── tools.py             # 8 tool definitions (7 banking + 1 auth helper)
│   ├── monzo_client.py      # Async API client with retry
│   ├── auth.py              # OAuth token management, loopback listener, auto-refresh
│   └── .env.example
├── skills/monzo/
│   └── SKILL.md             # Domain knowledge for Claude
├── pyproject.toml           # Python packaging (pip/uvx)
├── LICENSE
└── README.md

Credential flow:

User provides                 Server handles internally
┌──────────────────┐         ┌──────────────────────────┐
│ MONZO_CLIENT_ID  │──env──▶ │ OAuth browser flow       │
│ MONZO_CLIENT_SECRET│       │ Token exchange            │
└──────────────────┘         │ Token refresh             │
                             │ Account auto-detection    │
                             │ ~/.monzo-mcp/tokens.json  │
                             └──────────────────────────┘

Security:

• Read-only — no write operations, no fund transfers

• Credentials stored locally only, never transmitted beyond the Monzo API

• Token file restricted to user permissions (0600)

• Automatic token refresh on expiry

• Exponential backoff on rate limits

Important Notes

• 90-day limit: Due to Monzo's Strong Customer Authentication (SCA), transaction history is limited to 90 days. After approving SCA in the Monzo app, full history is accessible for 5 minutes before reverting to the 90-day window.

• Personal use only: The Monzo API is restricted to personal use — Monzo does not allow public applications.

• Rate limits: Monzo enforces rate limits. The client handles retries automatically.

• Amounts: All API amounts are in minor units (pence for GBP). Claude converts to pounds.

Changelog

• v1.1.1 — Reorganized installation docs: plugin-first ordering, uvx for generic JSON config

• v1.1.0 — Secure token storage: OAuth tokens stored in system keychain (with plaintext fallback), auto-migrates existing tokens

• v1.0.9 — Plugin credentials via keychain: userConfig prompts at enable time, stores securely in system keychain

• v1.0.8 — Seamless plugin onboarding: credentials read from ~/.monzo-mcp/config.json, interactive setup via SessionStart hook

• v1.0.7 — Security hardening (OAuth state nonce, bind 127.0.0.1, XSS escaping), code quality fixes, docs refresh

• v1.0.6 — Include decline_reason in list_transactions output

• v1.0.5 — Make MCP server client-agnostic

• v1.0.4 — Polished OAuth callback pages with SCA reminder

• v1.0.3 — Lazy account ID detection after SCA approval

• v1.0.2 — Add monzo_complete_auth tool for WSL/Docker callback fallback

• v1.0.1 — Bug fixes

• v1.0.0 — Initial release

License

MIT