Otis MCP

The source code of Otisbase, a free MCP server for client billing, built for consultants and small agencies.

Otis has no app or dashboard. Your AI assistant is the interface: it records clients, work, expenses and payments in Otis, and issues the invoices you approve. Otis stores the records and enforces the rules. It numbers invoices, calculates totals, requires your exact total before it issues an invoice, and never rewrites an issued invoice. Otis runs no AI model; every result comes from the records and the rules in this repository.

This repository is the complete service that runs at mcp.otisbase.com: the MCP server, email sign-in and the storage layer. It runs on Cloudflare Workers. The otisbase.com website is maintained separately.

Use the hosted service

Add this URL as a remote MCP server in your assistant:

https://mcp.otisbase.com/mcp

Sign-in uses OAuth with an email code, so there is no API key. How to install has a guide for Claude, ChatGPT, Claude Code, Codex, Cursor, Muse, Grok Bot and Mistral Vibe. The hosted service is free. Records are stored in the EU.

• MCP docs: the endpoint, the rules and every tool.

• Otis plugins, a menu and nine workflow skills for each assistant: Claude, ChatGPT and Codex, Grok and Cursor and other agents.

• Skills: what each skill does.

Related MCP server: holdings-mcp

What Otis records

How it works

Every business operation checks the caller's current membership. Amounts are integers in minor units. Writes take a request ID, so a retried call does not record the same fact twice.

Repository layout

Read the MCP docs before you change behavior. The rules agents follow are in src/docs.ts, src/descriptions.ts and src/workflows.ts, and the tests in test/ show the rules the server enforces.

Develop

You need Node 24 or newer.

npm ci
npm run check
npm test

Tests run in Cloudflare's local runtime. Email delivery is simulated in tests.

To run the Worker locally:

npm run dev -- --local --ip 127.0.0.1 --port 8788

Then open http://127.0.0.1:8788/health. The local runtime uses local storage only.

The plugins for each assistant are generated from src/workflows.ts in the private project and published as their own repositories; Skills links them.

Self-host

You can run your own copy on a Cloudflare account. Edit wrangler.jsonc before you deploy:

1. Set account_id to your Cloudflare account.

2. Create a KV namespace for OAuth state and put its ID in kv_namespaces. For EU storage, create it in the EU jurisdiction.

3. Replace the two routes with your own domains.

4. Set the vars:

   • ORIGIN: the URL of the MCP host.

   • SITE_ORIGIN: the URL of your website. Website pages opened on the MCP host redirect there, and the sign-in pages link to its Terms and Privacy Policy.

   • EMAIL_FROM: the sender for sign-in codes. The domain must be set up for Cloudflare Email Sending.

   • FEEDBACK_TO: the address that receives feedback sent through the feedback_send tool.

   • DO_JURISDICTION: eu keeps Durable Objects in the EU. Remove it to let Cloudflare choose.

   • SIGN_IN_ENABLED: true to allow sign-in.

5. Set ratelimits.namespace_id to an ID that is unique in your account.

Then deploy:

npx wrangler login
npm run deploy

The sign-in pages and emails name Otisbase. Change them in src/html.ts, src/auth.ts and src/notify.ts, and publish your own terms and privacy policy, before you offer your copy to other people.

Contribute

Bug reports, fixes and ideas are welcome. See CONTRIBUTING.md. To report a security problem, see SECURITY.md. You can also send feedback from your assistant: ask it to send feedback to Otis.

License

The code is released under the MIT License.

These items are not covered by the MIT License:

• The Otisbase and Otis names and logos.

• The Geist fonts in src/fonts/, under the SIL Open Font License.

The copy and check icons in src/html.ts come from Phosphor Icons (MIT).