Holiday Calendar MCP server

Small Business MCP Starter Kit by Modern Mustard Seed

Ship a remote MCP connector for Claude that is built to pass Anthropic's directory review on the first try.

This kit is the set of patterns Modern Mustard Seed uses for the connectors it runs in production, pulled out into a clean Next.js project you can fork:

• A route template on Next.js App Router and mcp-handler, serving Streamable HTTP at one URL per connector, with no redirect.
• Tool conventions enforced at load time: a title, readOnlyHint or destructiveHint on every tool, snake_case names of 64 characters or fewer, and descriptions that describe instead of steer. Break a rule and pnpm test fails, long before a reviewer sees it.
• Specific error messages instead of "Bad Request", and output size caps under Claude's limits.
• Rate limiting built for Claude's shared egress range. Every claude.ai user arrives from 160.79.104.0/21, so nothing is keyed by IP and nothing returns HTTP 429.
• An SSRF-safe fetch for any tool that reads a URL a user supplied, with tests that prove a listening loopback server receives zero requests.
• An eval harness that runs real prompts against your live URL, with no model and no API key.
• Docs, privacy, terms and support page templates plus /.well-known/security.txt, all driven by one config file.
• A submission checklist mapped to the directory form's 10 steps and its seven policy acknowledgments, with every rule linked to Anthropic's documentation.
• A worked example: a U.S. federal holiday and business-day calendar with five read-only tools that passes all 35 of its own evals.

MIT licensed. Built by Modern Mustard Seed.

Working demo

The example connector runs live, deployed from this repository with no changes:

• Connector URL: https://starter.modernmustardseed.com/holidays (add it in Claude under Customize > Connectors > Add custom connector)
• Docs page reviewers read: https://starter.modernmustardseed.com/docs/holidays
• Privacy, terms and support: https://starter.modernmustardseed.com/privacy, /terms, /support
• Official MCP Registry entry: com.modernmustardseed/holiday-calendar

Run the evals against it yourself: node eval/holidays.eval.mjs https://starter.modernmustardseed.com

Quickstart: 10 minutes

You need Node 22.6 or later, pnpm, and a Vercel account (any host that runs Next.js works).

1. Make your copy. (1 minute)

gh repo create my-connector --template ModernMustardSeed/small-business-mcp-starter --public --clone
cd my-connector
pnpm install

Or select Use this template on GitHub.

2. Run it and prove it works. (2 minutes)

pnpm dev

In a second terminal:

pnpm test
pnpm evals http://localhost:3000

You should see 32 pass from the unit tests and 35 of 35 passed from the evals. Open http://localhost:3000/docs/holidays to see the docs page reviewers read.

3. Make it yours. (2 minutes)

Edit lib/site.ts: company name, location, website, support inbox, security inbox, and the policy date. Every public page and security.txt read from it. Replace app/icon.svg and app/apple-icon.png with your own mark; the directory listing asks for an icon.

4. Deploy. (3 minutes)

Import the repository at vercel.com/new, or from the terminal:

vercel deploy --prod

Vercel sets VERCELPROJECTPRODUCTION_URL, which the pages use for their links. Leave Attack Challenge Mode and any bot-protection rule off for your MCP paths: they answer Claude with a challenge page.

5. Check the deployment. (1 minute)

Shortened. The full README is on GitHub.