Holiday Calendar
U.S. federal holidays and business-day math for deadlines and schedules
Provides U.S. federal holidays with observed dates, checks whether dates are business days, and calculates business days between dates or from a starting point, skipping weekends and holidays.
Try asking Muse: "How many business days do I have to deliver this order by next Friday?"
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Source: Found in the official MCP Registry (com.modernmustardseed/holiday-calendar) · First listed October 29, 2026
Last 24 hours
Each bar is one check, every 15 minutes. Green means it answered. Last checked 57 min ago.
Is it safe to connect?
What Muse can see: It does not ask you to sign in, so it cannot see your accounts. It only sees what Muse sends it from your request.
Before it acts: Read what Muse plans to do before you approve it, and remove the app from Muse when you stop using it.
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How to add it to Muse
Not in Muse's Connectors list yet, but Muse can still use it. Copy the request below and paste it into Muse. Muse asks before it shares anything with the app's site. Meta does not review apps used this way, so only use ones you trust. We tested this in the Muse app on September 24, 2026: Muse used an app's link directly this way and returned a live answer.
https://starter.modernmustardseed.com/holidaysNot in Muse's Connectors list yet. Muse can still use it: its page gives you a request to paste into Muse.
Also use it in ChatGPT or Claude
Holiday Calendar is a remote MCP server, so any assistant that can add a custom connector by link can use it. Same link, same tools.
Add it to ChatGPT
- 1
Open ChatGPT settings
In ChatGPT, open Settings, then Connectors (called Apps & Connectors on some accounts).
- 2
Turn on developer mode
Under Advanced settings, switch on Developer mode. That is what lets you add a connector by link.
- 3
Create the connector
Choose Create, give it a name, paste the link as the MCP server URL, and save. If it needs a sign-in, ChatGPT asks for it here.
- 4
Use it in a chat
Start a chat, open the tools menu, pick the connector, and ask. ChatGPT asks before it runs a tool the first time.
Custom connectors need a paid ChatGPT plan, and on Team, Enterprise and Edu accounts only an admin can add them. Our "Working" label means the server answered us; it cannot tell whether your plan lets you add it. All connectors that work in ChatGPT
Add it to Claude
- 1
Open Claude settings
In Claude, open Settings, then Connectors.
- 2
Add a custom connector
Choose Add custom connector, give it a name, and paste the link.
- 3
Connect and use it
If it needs a sign-in, Claude sends you to it. Then turn the connector on in a chat from the tools menu and ask.
Custom connectors are available on paid Claude plans; on Team and Enterprise accounts an admin may need to add them. Our "Working" label means the server answered us; it cannot tell whether your plan lets you add it. All connectors that work in Claude
https://starter.modernmustardseed.com/holidaysWhat people ask Muse to do
Technical details: safety screening, tools, response time and recent checks
Response time at the last check: 186ms. Worked in 100% of checks over 30 days.
Screening · October 29, 2026
Screened, no issues found
Screening looks for known threats and hidden instructions at the time of the check, and runs again weekly and whenever the tool list changes. It cannot see the server's code, so only connect what you need and review what Muse asks to do. How screening works.
Tools · 5
list_federal_holidaysList 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, fromnext_federal_holidaysFind 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.check_business_dayCheck 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.add_business_daysMove 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 icount_business_daysCount 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.Recent checks
Link
https://starter.modernmustardseed.com/holidaysQuestions about Holiday Calendar in Muse
How do I connect Holiday Calendar to Muse?
Not in Muse's Connectors list yet, but Muse can still use it. Paste this into Muse: "Use Holiday Calendar to help me. It is a free service with an MCP server at https://starter.modernmustardseed.com/holidays. It does not need an API key. Ask me before you share anything with it." Muse asks before it shares anything with the app's site. Meta does not review apps used this way, so only use ones you trust. We tested this in the Muse app on September 24, 2026: Muse used an app's link directly this way and returned a live answer.
Is Holiday Calendar working right now?
At the last check (October 29, 2026, 11:00 UTC) the endpoint was working, answering in 186ms. Over the last 7 days it answered 100% of health checks. It is checked every 15 minutes.
Is Holiday Calendar safe to connect to Muse?
It was screened on October 29, 2026 with the result "screened, no issues found". Screening checks the domain against threat feeds and reads the tools for hidden instructions and requests for passwords or card numbers. It cannot see the server's code, so grant only the access you need.
What can Holiday Calendar do in Muse?
It exposes 5 tools, including list_federal_holidays, next_federal_holidays, check_business_day, add_business_days. For example, you could ask Muse: "How many business days do I have to deliver this order by next Friday?"
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This listing was added from public sources (Found in the official MCP Registry (com.modernmustardseed/holiday-calendar)). If you build Holiday Calendar, claim it to correct the details and get your badge.
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