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Holiday Calendar MCP Server

by modernmustardseed Your server? Claim it
answering

Holiday Calendar is answering right now. Last checked 2 min ago. It exposes 5 tools.

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

Uptime history 4 hours of history
4 hours agonow
100.0%
Uptime 24h
12 of 12 checks
5
Tools
read from the server
307 ms
Response time
average over 24h
open, no key
Access
streamable-http

Nothing serious here today

Today is the operative word: we check Holiday Calendar every 15 minutes and re-read its code on every release. Watch it and you find out the day that stops being true.

Three servers free · no card

Connect this server

Endpoint below is the one we actually reach during checks — not the one copied from a README. Last verified 2 min ago.

run in your terminal
claude mcp add holiday-calendar --transport http https://starter.modernmustardseed.com/holidays
~/Library/Application Support/Claude/claude_desktop_config.json
{
  "mcpServers": {
    "holiday-calendar": {
      "url": "https://starter.modernmustardseed.com/holidays"
    }
  }
}
~/.codex/config.toml
[mcp_servers.holiday-calendar]
url = "https://starter.modernmustardseed.com/holidays"
.cursor/mcp.json
{
  "mcpServers": {
    "holiday-calendar": {
      "url": "https://starter.modernmustardseed.com/holidays"
    }
  }
}
.vscode/mcp.json
{
  "mcpServers": {
    "holiday-calendar": {
      "url": "https://starter.modernmustardseed.com/holidays"
    }
  }
}

Available tools 5

Read directly from the server with tools/list, grouped by what they act on. If a tool disappears, we record the date.

business
add_business_days
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 the resulting date and every holiday it skipped. Up to 1,000 business days either way.
check_business_day
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
count_business_days
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.
federal
list_federal_holidays
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 it to answer which days federal offices close in a year.
next
next_federal_holidays
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.

Endpoints

URLTransportStateLatencyChecked
https://starter.modernmustardseed.com/holidays streamable-http answering 229 ms 2 min ago

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answering

Holiday Calendar — questions

Answers built from our own checks of this server.

What can Holiday Calendar do?
It exposes 5 tools, read directly from the server on our last check. Among them: add_business_days, check_business_day, count_business_days, list_federal_holidays, next_federal_holidays. The full list with descriptions is on this page — we take it from the server itself via tools/list, not from a README. How MCP servers expose tools in the first place →
Is Holiday Calendar working right now?
We send a real MCP handshake every 15 minutes. Over the last 24 hours 12 of 12 checks got a reply (100.0%), average response time 307 ms. The bar chart above shows every period we have measured.
How do I connect Holiday Calendar?
Copy the ready config from this page — we generate it for Claude Code, Claude Desktop, Codex, Cursor and VS Code, each with the file path that client actually reads. It is a remote server, so there is nothing to install — the client connects to the address.
Does Holiday Calendar need an API key?
No. Holiday Calendar completed a full MCP handshake with us as an anonymous client and listed its tools without asking for anything. All 5 of them are readable on this page. This is what we observed, not what the docs claim.
How fast is Holiday Calendar?
It answers our handshake in 307 ms on average, which is faster than 47% of all working MCP servers we measure. The comparison comes from our own checks across the whole registry, every 15 minutes.