Catón AI

A local-first, plugin-based financial watchdog for individuals and small businesses.

Catón AI connects to where your money actually goes — bank accounts, cards and the usage APIs of the services you pay for — keeps everything on your own machine, and lets plugins and AI agents watch it for you: budgets, goals, cash-flow forecasts, and alerts such as "tell me when my Anthropic spend goes over $20".

Status: pre-alpha. A first command-line version syncs European bank accounts through Enable Banking into a local ledger, reports monthly outflows and serves the ledger read-only to AI assistants over MCP. Plugins, agents, alerts and the web UI are not built yet.

Why the name

Cato the Elder was the Roman censor famous for his austerity and for reprimanding waste. Catón AI plays the same role for your finances: it keeps watch, and it tells you when something is off.

Related MCP server: Beanquery MCP Server

Principles

• Local-first and private. Data and credentials stay on your machine. No telemetry.

• Minimal core, everything else is a plugin. Data sources, budgets, goals and watchdog agents are plugins, including the official ones.

• Permissions, not trust. Plugins declare what they can read, write and whether they may use the network; nothing gets network access by default.

• Reviewed before activation. Plugins are checked automatically — including an AI-assisted security and functionality review — before they touch your data.

Documentation

• Architecture (arc42 + C4)

• Architecture Decision Records

Engineering standards

Enforced standards run through npm run check locally and in CI on every pull request; main cannot change unless they all pass. Each gate was verified to fail on a deliberate violation when it was introduced.

Architecture and code

Security and supply chain

Process

Planned

Getting started

Requires Node.js 24 LTS or newer and an Enable Banking application in restricted mode with your own accounts linked and authorised (one session per bank).

Create ~/.config/caton-ai/config.json, readable only by you (chmod 600). Each entry is an instance of a plugin; its secret variables are never written here:

{
  "instances": [
    {
      "id": "mybank",
      "title": "My bank",
      "plugin": "enable-banking",
      "settings": {"app-id": "<application id>", "session-id": "<authorised session id>"}
    }
  ]
}

Secrets go in an encrypted store (ADR 0017) as plugin:instance:variable, here enable-banking:mybank:private-key. One secret can serve several instances: save it under a name of your choice and enter ${that-name} as their value (ADR 0019). The web interface lists every secret an instance needs, with what it is and where to get it:

npm run build           # builds the web interface once
npm start -- serve      # prints a one-time link to http://127.0.0.1:7170

See ADR 0018 for how it is protected. A configuration in the first format (plugins and connections) is converted with npm start -- config migrate.

npm ci --ignore-scripts
npm start -- sync       # fetch accounts, movements and balances into the local ledger
npm start -- accounts   # accounts and latest balances
npm start -- spend 3    # money leaving your accounts per month, last 3 months (cash basis)
npm start -- status     # last sync of every connection

Outflows still include transfers between your own accounts; transfer detection and categorisation are next. Unattended PSD2 access allows only a few requests per account per day (the exact quota is still to be verified), so sync at most once or twice a day. Current limitations are tracked in ADR 0012.

Ask your AI assistant (MCP)

caton mcp serves the ledger read-only over the Model Context Protocol (specification 2026-07-28; hosts still on 2025-era versions are served too). It never contacts a bank, amounts are exact decimals, and every answer says whether the figures are complete. See ADR 0013.

Register it in your MCP host with absolute paths; the host must start Node.js 24 or newer, which may not be the node on its PATH. For Claude Code:

claude mcp add caton-ai -- /path/to/node24/bin/node /path/to/caton-ai/packages/cli/src/main.ts mcp

For hosts configured with JSON, such as Claude Desktop:

{
  "mcpServers": {
    "caton-ai": {
      "command": "/path/to/node24/bin/node",
      "args": ["/path/to/caton-ai/packages/cli/src/main.ts", "mcp"]
    }
  }
}

Account names, descriptions and counterparties come from banks and third parties; the server tells the assistant to treat them as data, never as instructions. With a hosted model, what the tools return is sent to its provider.

Development

Requires Node.js 24 LTS or newer.

npm ci --ignore-scripts
npm run check   # types, lint, format, architecture rules, dead code, web build, tests + coverage

See CONTRIBUTING.md for the quality gates and conventions.

Security

Please report vulnerabilities privately as described in SECURITY.md.

License

MIT © César Zea