Holiday Calendar — Claude Code MCP server: install
This MCP server handles U.S. federal holidays, observed dates, and business-day calculations. Use it when an agent needs a date based on working days.
claude mcp add --transport http holiday-calendar https://starter.modernmustardseed.com/holidaysWhat Holiday Calendar does
Holiday Calendar gives an AI client access to a U.S. federal holiday calendar. It accounts for observed holiday dates and can calculate business-day offsets, such as finding when an invoice becomes due.
The sample connector exposes five read-only tools over HTTP at https://starter.modernmustardseed.com/holidays. It can be connected to Claude Code, Codex, Cursor, GitHub Copilot, Gemini CLI, and the other listed clients. A self-hosted setup following the kit’s deployment path relies on Node 22.6 or newer, pnpm, and a Vercel account.
What it helps with
- calculate a due date from a number of business days
- account for an observed U.S. federal holiday
- check whether a date is a business day
- find upcoming U.S. federal holidays
Example prompts for the agent
- Calculate the due date for an invoice dated 2026-11-20 with a 10-business-day term.
- Check whether 2026-11-26 is a U.S. federal holiday.
- List upcoming U.S. federal holidays together with their observed dates.
How to install Holiday Calendar
Platform CLI: remote server
claude mcp add --transport http holiday-calendar https://starter.modernmustardseed.com/holidaysPlatform CLI: remote server
codex mcp add holiday-calendar --url https://starter.modernmustardseed.com/holidaysConfig file
{
"mcpServers": {
"holiday-calendar": {
"url": "https://starter.modernmustardseed.com/holidays"
}
}
}Config file
{
"servers": {
"holiday-calendar": {
"type": "http",
"url": "https://starter.modernmustardseed.com/holidays"
}
}
}Platform CLI: remote server
gemini mcp add -t http holiday-calendar https://starter.modernmustardseed.com/holidaysStep by step, with commands for each platform: How to add an MCP server to Claude Code, Codex, Cursor, VS Code, Gemini CLI and more
Questions about Holiday Calendar
How do I install Holiday Calendar in Claude Code?
Run claude mcp add --transport http holiday-calendar https://starter.modernmustardseed.com/holidays.
What does Holiday Calendar do?
It provides U.S. federal holiday dates, includes observed-date handling, and calculates business-day offsets. The sample connector has five read-only tools.
What is required to deploy a copy?
The kit’s deployment path uses Node 22.6 or newer, pnpm, and a Vercel account.
