The Scenario
You are a project manager at a software consultancy. The delivery team just finalized 30 milestone dates for a multi-country rollout. The clients are in 8 countries, each with their own public holidays and working-day conventions. Before you confirm the delivery schedule, you need to verify that every proposed date is actually a working day in each target country.
The kick-off call where you present the schedule is Monday morning. It is Friday afternoon.
The bad version of this weekend:
- You open a public holiday site for Germany, check January 6, mark it down
- Switch to a France holiday calendar for the same date
- Realize there is no single authoritative source for all 8 countries
- Build a manual grid by hand, copying from 8 different browser tabs
- By 6 PM Friday you have checked 12 of 30 dates across 4 of 8 countries
- Monday morning, you present a schedule where two milestones land on bank holidays in the UK and a national day in Brazil.
The client-safe version is one prompt.
The Easy Way: One Prompt in SheetXAI
SheetXAI is an AI agent inside your spreadsheet. It reads your milestone dates and country list and calls the API Ninjas public holiday endpoint to fill a working-day grid without you touching a browser.
Open the SheetXAI sidebar and type:
For each date in column A and each country code in row 1, check whether it is a working day using API Ninjas and fill the grid with "Yes" or "No."
SheetXAI calls the API Ninjas holiday endpoint for each date-country combination, resolves weekends and public holidays, and populates the grid.
What You Get
A milestone-by-country working-day grid:
- Rows = proposed milestone dates from column A
- Columns = country codes from row 1
- Cells = "Yes" (working day) or "No" (holiday or weekend) for each combination
Any "No" stands out immediately before you paste the schedule into the client deck. No manual calendar checking, no missed national holidays.
Want the full public holiday list per country for the year? Ask in the same prompt.
What If the Data Is Not Quite Ready
Project schedule sheets have their own kind of messiness. SheetXAI handles it alongside the holiday checking.
When the date format is inconsistent
Some dates are in MM/DD/YYYY format, some in DD-MMM-YYYY, some in ISO.
Normalize all dates in column A to ISO format (YYYY-MM-DD) before checking working days. Then fill the country grid as described.
When you want to pull the full public holiday list for planning
You want to see every holiday for each country for the year, not just the yes/no for proposed dates.
Pull all public holidays for the countries in column B for the year 2026 using API Ninjas and list each holiday name and date in adjacent columns. Then check which of my proposed milestone dates in column A fall on those holidays.
When you want to suggest the next working day for each conflict
Instead of just flagging "No," you want a replacement date.
For each date-country cell in my grid marked "No," find the next working day in that country using API Ninjas and write it as a suggestion in a separate grid below, prefixed with "Suggest: ".
When the full schedule validation is one prompt
Thirty dates, eight countries, normalize formats, fill the grid, flag conflicts, and suggest replacements all before the Monday call.
Normalize all dates in column A to ISO format. For each date and each country code in row 1, check whether it is a working day using API Ninjas and fill the grid with "Yes" or "No." For any "No" cell, find the next working day in that country and write it in a second grid below, prefixed with "Suggest: ". Highlight any row in the date column where more than 3 countries show "No."
The pattern: format normalization, grid population, and conflict resolution all in one instruction so you walk into Monday with a clean schedule.
Try It
Get the 7-day free trial of SheetXAI and open any project schedule or milestone sheet, then ask SheetXAI to validate dates against public holidays using API Ninjas. The API Ninjas integration is included in every SheetXAI plan. See also how to geocode a bulk city list or the API Ninjas in Google Sheets overview.