Holiday Calendar MCP

An official MCP server by Modern Mustard Seed that provides tools to list U.S. federal holidays, check business days, and calculate business day intervals based on 5 U.S.C. 6103. It enables agents to answer date-related questions for small businesses without model guessing.

Endpoint and access

No sign-in: your client connects and lists tools immediately, with no account or key.

No sign-inEndpoint checked 2026-10-18Operated by Modern Mustard Seed LLC

MCP endpoint (Streamable HTTP)

https://starter.modernmustardseed.com/holidays

Vendor documentation

What you can do with it

List federal holidays for a specific year
Calculate due dates by adding business days
Count business days between two dates
Check if a date is a business day

Tools advertised by the last live check:

list_federal_holidays
next_federal_holidays
check_business_day
add_business_days
count_business_days

Connect from your client

Each snippet registers the same endpoint; pick the client you use.

This server is operated by the named third party. Listing and endpoint checks are not an endorsement or a security audit. Review the operator's permissions, terms, and data handling before connecting. How listings are checked and corrected.

Claude Code

Run this once in a terminal. It registers a Streamable HTTP server. Use --scope project to write .mcp.json for the repo.

Claude Code configuration

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

Codex

Run this once. Codex stores MCP servers in ~/.codex/config.toml (or .codex/config.toml in a trusted project).

Codex configuration

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

Cursor

Merge this server into .cursor/mcp.json in your project, then enable holiday-calendar-mcp in your MCP settings.

Cursor configuration

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

Cline

Merge this into cline_mcp_settings.json (Cline → MCP Servers → Configure). The type must be streamableHttp for a remote HTTP server.

Cline configuration

{
  "mcpServers": {
    "holiday-calendar-mcp": {
      "type": "streamableHttp",
      "url": "https://starter.modernmustardseed.com/holidays",
      "disabled": false
    }
  }
}

VS Code

Merge this server into .vscode/mcp.json. Use MCP: List Servers to start holiday-calendar-mcp and inspect its tools.

VS Code configuration

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

Gemini CLI

Run this once. It writes .gemini/settings.json in the current project; pass --scope user for ~/.gemini/settings.json.

Gemini CLI configuration

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

Claude Desktop

Merge this into claude_desktop_config.json (macOS: ~/Library/Application Support/Claude/, Windows: %APPDATA%\Claude\), then restart Claude Desktop.

Claude Desktop configuration

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

Windsurf

Merge this into ~/.codeium/windsurf/mcp_config.json, then refresh MCP in Cascade. Windsurf remote servers use serverUrl, not url.

Windsurf configuration

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

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