ISO date observed shift

iso-date-observed-shift · version 1.0.0 · Dates & times (UTC, ISO 8601) · free, no key needed

Shift a date forward or backward until it lands on a day that is neither a weekend nor a caller-supplied holiday.

Use when you need to: iso date observed shift · holiday observed date · move holiday off weekend.

Supported

• iso date observed shift
• holiday observed date
• move holiday off weekend

Not supported

• built-in national holiday calendars
• nearest-day tie-break rules
• timezones

Behavior

• date is a strict YYYY-MM-DD proleptic Gregorian UTC calendar date with year 0001-9999.
• weekend_days is an array of ISO weekday integers 1-7, unique, at most 6 entries (at least one non-weekend weekday must remain). holidays is an array of unique YYYY-MM-DD dates, at most 366 entries.
• direction is "forward" or "backward".
• If date is not in weekend_days and not listed in holidays, the result is date unchanged.
• Otherwise the date steps one calendar day at a time in the given direction until it lands on a day that is in neither weekend_days nor holidays.
• The call is rejected if a step would move outside year 0001-9999.

Input

• date (string, required): min length 10; max length 10; pattern ^\d{4}-\d{2}-\d{2}$
• weekend_days (array of integer, required): max items 6; each min 1; each max 7
• holidays (array of string, required): max items 366; each min length 10; each max length 10
• direction (one of "forward", "backward", required)

Output

• date (string, required): min length 10; max length 10

Limits

• year min: 1
• year max: 9999
• max weekend days: 6
• max holidays: 366

Example

Request input:

{
  "date": "2026-09-19",
  "weekend_days": [
    6,
    7
  ],
  "holidays": [],
  "direction": "forward"
}

Response:

{
  "result": {
    "date": "2026-09-21"
  }
}

How to call it

MCP

Connect https://computefirst.net/mcp (setup), then call execute with:

{
  "id": "iso-date-observed-shift",
  "version": "1.0.0",
  "input": {
    "date": "2026-09-19",
    "weekend_days": [
      6,
      7
    ],
    "holidays": [],
    "direction": "forward"
  }
}

HTTP (no key)

curl -X POST https://computefirst.net/v1/tools/iso-date-observed-shift/versions/1.0.0/execute \
  -H "Content-Type: application/json" \
  -d '{"date":"2026-09-19","weekend_days":[6,7],"holidays":[],"direction":"forward"}'

The machine-readable contract is at /v1/tools/iso-date-observed-shift/versions/1.0.0.

CLI

node cli.mjs run iso-date-observed-shift 1.0.0 --input input.json --base-url https://computefirst.net

Get the client at /clients/cli/.

Related tools

• ISO date add months: Add a signed month count to a YYYY-MM-DD date, clamping the day to the target month.
• ISO date add years: Add a signed whole-year delta to a YYYY-MM-DD date, clamping the day if 29 February has no match.
• ISO date add: Add a signed whole-day delta to a strict YYYY-MM-DD calendar date.
• ISO date age: Compute the calendar-aware elapsed years, months, and days between a birth date and an as-of date.
• ISO date business day add: Add a signed count of business days to a date, skipping caller-supplied weekend weekdays and holidays.
• ISO date business days count: Count the business days in an inclusive date range, skipping caller-supplied weekend weekdays and holidays.