MCP server

Holiday Calendar

com.modernmustardseed/holiday-calendar

Checked 26 Oct 2026, 08:29 UTC · Connected to it and listed its tools

U.S. federal holidays with observed dates and business-day math. Example from an open-source kit.

Website Source

At a glance

Type

MCP server

Publisher

modernmustardseed.com (verified by the MCP Registry)

Status

Working at last check

Tools

5

Token cost

About 1,067 tokens per request

Sets up in

Claude Code, Claude Desktop, Codex, Gemini CLI, Cursor, VS Code, Antigravity, ChatGPT, OpenAI API, Grok

Last checked

26 Oct 2026, 08:29 UTC

Connect it to your agent

Add to CursorAdd to VS CodeVS Code Insiders

Opens the app, which shows the server and asks you to confirm. For other apps, copy the setup below.

Claude Code

claude mcp add --transport http holiday-calendar https://starter.modernmustardseed.com/holidays

Claude Desktop

Settings → Connectors → Add custom connector, and paste the URL.

Codex (config.toml)

[mcp_servers.holiday-calendar]
url = "https://starter.modernmustardseed.com/holidays"

Gemini CLI

{"mcpServers":{"holiday-calendar":{"httpUrl":"https://starter.modernmustardseed.com/holidays"}}}

Cursor

{"mcpServers":{"holiday-calendar":{"url":"https://starter.modernmustardseed.com/holidays"}}}

VS Code

{"servers":{"holiday-calendar":{"type":"http","url":"https://starter.modernmustardseed.com/holidays"}}}

Antigravity

agy mcp add holiday-calendar https://starter.modernmustardseed.com/holidays

ChatGPT

Settings → Apps & Connectors → Advanced settings: turn on Developer mode, then Create a connector and paste the URL. Which plans can do this varies.

OpenAI API (Responses tools)

{"type":"mcp","server_label":"holiday-calendar","server_url":"https://starter.modernmustardseed.com/holidays","require_approval":"always"}

Grok (xAI API tools)

{"type":"mcp","server_label":"holiday-calendar","server_url":"https://starter.modernmustardseed.com/holidays"}

Tools

• add_business_days ~288 tokens
  Move a number of U.S. business days forward or backward from a date, skipping weekends and observed federal holidays, for due dates, delivery windows and notice periods. The start date is not counted: 1 business day after a Friday is the next Monday, or Tuesday when that Monday is a holiday. Returns
• check_business_day ~150 tokens
  Check whether a date is a U.S. business day (a weekday that is not an observed federal holiday). Returns the weekday, the holiday observed that day if any, and the business days just before and just after it.
• count_business_days ~232 tokens
  Count the U.S. business days between two dates, both dates included, leaving out weekends and observed federal holidays. Returns the business day count, the weekend days, and each holiday that fell in the span. Spans up to 3,660 calendar days.
• list_federal_holidays ~189 tokens
  List the eleven U.S. federal holidays for one calendar year (2021 through 2100): each holiday's name, its actual date and weekday, the date it is observed when it falls on a weekend (Saturday moves to the Friday before, Sunday to the Monday after), and the rule that sets it, from 5 U.S.C. 6103. Use
• next_federal_holidays ~208 tokens
  Find the next one to eleven U.S. federal holidays observed on or after a date, with each one's observed date and how many calendar days away it is. Without from_date it starts from today's date in America/New_York and says which date it used.

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Badge for your README

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