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External MCP servers

MCP (Model Context Protocol) is a standard way for an app to offer tools to an AI assistant. Many services now publish an MCP server — accounting, payments, market data, a full web browser — and connecting one gives Lucius whatever tools that server offers.

This is the most powerful connector in the app, and the one that deserves the most care: a server you connect is someone else’s software, and what it returns goes straight into Lucius’s conversation. Only connect servers you trust, and start every tool at Needs approval (the default).

There are two kinds:

  • Remote server (URL) — a service hosted by the vendor. You give its address and, usually, sign in or paste a key.
  • Local command (stdio) — a program the app starts on this machine, such as npx -y @playwright/mcp@latest. It runs with the same access to this computer as Open Net Worth itself.

Add a server from the directory

The directory includes ready-made entries — Playwright (a real web browser), Firecrawl, Stripe, QuickBooks Online, Xero, Mercury, Expensify, Avalara AvaTax, Twelve Data, SEC EDGAR and FRED.

  1. Open Connectors in the sidebar, click Browse & add, and choose MCP.
  2. Click a card to read what it does and which tools it offers, then click Add. The connection form opens with the address or command already filled in.
  3. Fill in what the server needs:
    • OAuth servers (Mercury, Expensify, Avalara, Twelve Data): click Connect and sign in to the vendor in the window that opens.
    • API key servers (Stripe): paste the key into API key. For Stripe, a restricted key with only the permissions you want is the safer choice.
    • Local commands with Environment variables (optional) pre-listed (Firecrawl, Xero, SEC EDGAR, FRED): fill in the value after each =, for example FRED_API_KEY=abc123. Get the value from the vendor — the card’s Documentation or Source repository link says where.
  4. Click Connect. The app starts the server, checks it answers, and lists its tools — Testing connection to … and listing tools…. A local command can take a few minutes the first time while its package downloads.
  5. Review the tools it found. Each starts at Needs approval; change any to Always allow or Blocked if you want. Click Add server.

The toast ”… added — N tools ready for Lucius” confirms it. Nothing is saved until the connection test succeeds.

QuickBooks Online has no ready-made settings — follow the links on its card for the vendor’s own instructions, and enter what they give you in the form (or add it as a custom server, below).

Add any other server

  1. Connectors → Browse & add → MCP → Custom MCP server.
  2. If the server’s README has a JSON config block (the "mcpServers": { … } kind), click Paste from a config snippet and paste it — the fields below fill themselves in. Otherwise:
  3. Pick a Transport:
    • Remote server (URL) — enter the Server URL (starting with https://, or http:// for a server on your own machine), then choose Authentication: None, API key (sent to the server as a bearer token), or OAuth (you sign in to the vendor in a pop-up).
    • Local command (stdio) — enter the Command (for example npx or uvx), the Arguments (for example -y @modelcontextprotocol/server-filesystem /path/to/folder) and any Environment variables, one NAME=value per line.
  4. Click Connect, review the tools, and click Add server — the same as steps 4–5 above.

A local command needs its runtime installed on the machine running Open Net Worth — Node.js for npx, uv for uvx.

Check that it works

Ask Lucius to use it, for example after adding Playwright:

Open example.com in the browser and tell me what the page says.

The first time he uses each tool, you’ll get a card to approve it. The server’s page under Connectors lists its tools and their levels under Tool permissions.

Managing a server

Open the server under Connectors:

  • ⋯ (More actions) → Edit configuration — change the address, key, command or environment. The connection is tested again before anything is saved. A saved key is never sent back to your browser, so to re-test with it, reveal it with the eye icon or paste it again. The transport can’t be changed — add the server again instead.
  • ⋯ → Refresh tools list — pick up tools the server added since you connected it.
  • Pause / Resume — Lucius loses access to its tools while paused.
  • ⋯ → Remove connector — removes the server and its saved credentials.
  • Reconnect — appears if the server stopped answering or a sign-in expired.

Permissions — start cautious

Every tool from an MCP server starts at Needs approval: Lucius shows you exactly what he’s about to call and waits for you. You can change each tool’s level under Tool permissions, or by choosing Always allow on an approval card. See Permissions.

Tools are listed under Read-only tools or Write & delete tools. When the server marks a tool as read-only (or not), that’s the heading it gets; otherwise the app guesses from the tool’s name. The heading is only a label. It never changes a tool’s level or whether a call runs.

Always allow really means always — including inside a scheduled Automation with nobody watching. Only use it for a tool you’ve used enough to trust, and never for one that can change or send things (a payment, an invoice, an email) unless you’re sure. Remember the vendor can update their server at any time.

Risks, in plain terms

  • A local command can do anything you can do on this machine — read and write your files, use the network. It runs for as long as the connector is enabled, not just during a call. Only add commands from sources you trust, like any software you install.
  • A server’s answers can try to trick Lucius. Text from a third-party server is treated as data, never as instructions from you, and is cleaned and shortened before Lucius sees it. That lowers the risk; it doesn’t remove it — which is why approval is the default.
  • Some servers write to real accounts. Stripe, QuickBooks, Xero and Mercury tools can create or change records in those services. The directory card says so when that’s the case.

What protects you:

  • Lucius never sees the server’s full address or command line — only its host or program name — because a connection string often contains a password or key. You see the full details on the Connectors page.
  • Lucius can’t add a server, change one, or raise a tool’s permission. Only you can, from the Connectors page.
  • Keys, OAuth sign-ins and environment variables are stored on this machine only, never sent to the AI model, and left out of exports and sanitised backups.

Troubleshooting

“Could not reach the server.” — check the URL or command is right and the server is running. For a local command, the box under the spinner shows the command’s own output; an error there (for example command not found) usually means Node.js or uv isn’t installed.

“Enter a full URL, starting with http:// or https://.” — include the https:// part.

The test fails with an authorization error — the server needs credentials. Switch Authentication to API key or OAuth and try again.

OAuth: “Register this redirect URI with the vendor, then try again” — the vendor needs you to set up an app on their side. Register the address shown, then click Connect again.

OAuth: a Client ID field appears — this server doesn’t support automatic sign-up. Create an app registration at the vendor, paste its client ID, and try again.

“Sign in above, then test the connection.” — finish the OAuth sign-in before clicking Connect again.

Was connected — sign-in expired — click Reconnect (or Edit configuration) and sign in again.

It hangs on a first connect — a local command may still be downloading. If the output box has been quiet for a long time, click ‹ Back at the top, check the command, and try again.