ISO date weekday occurrences in range

iso-date-weekday-occurrences-in-range · version 1.0.0 · Dates & times (UTC, ISO 8601) · free, no key needed

List every date within an inclusive date range that falls on a given ISO weekday.

Use when you need to: iso date weekday occurrences in range · every monday between two dates · list matching weekdays in range.

Supported

• iso date weekday occurrences in range
• every monday between two dates
• list matching weekdays in range

Not supported

• multiple weekdays per call
• timezones
• locale weekday names
• recurring rules with exceptions

Behavior

• start and end are strict YYYY-MM-DD calendar dates with year 0001-9999. start must not be after end.
• weekday is a JSON integer 1-7 with Monday=1 .. Sunday=7.
• end minus start must not exceed 36600 days (about 100 years).
• dates lists every date d with start <= d <= end whose ISO weekday equals weekday, in ascending order.

Input

• start (string, required): min length 10; max length 10; pattern ^\d{4}-\d{2}-\d{2}$
• end (string, required): min length 10; max length 10; pattern ^\d{4}-\d{2}-\d{2}$
• weekday (integer, required): min 1; max 7

Output

• dates (array of string, required): each min length 10; each max length 10

Limits

• year min: 1
• year max: 9999
• max range days: 36600
• max occurrences: 5230

Example

Request input:

{
  "start": "2026-09-01",
  "end": "2026-09-30",
  "weekday": 1
}

Response:

{
  "result": {
    "dates": [
      "2026-09-07",
      "2026-09-14",
      "2026-09-21",
      "2026-09-28"
    ]
  }
}

How to call it

MCP

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

{
  "id": "iso-date-weekday-occurrences-in-range",
  "version": "1.0.0",
  "input": {
    "start": "2026-09-01",
    "end": "2026-09-30",
    "weekday": 1
  }
}

HTTP (no key)

curl -X POST https://computefirst.net/v1/tools/iso-date-weekday-occurrences-in-range/versions/1.0.0/execute \
  -H "Content-Type: application/json" \
  -d '{"start":"2026-09-01","end":"2026-09-30","weekday":1}'

The machine-readable contract is at /v1/tools/iso-date-weekday-occurrences-in-range/versions/1.0.0.

CLI

node cli.mjs run iso-date-weekday-occurrences-in-range 1.0.0 --input input.json --base-url https://computefirst.net

Get the client at /clients/cli/.

Related tools

• ISO date range list: Enumerate the dates in an inclusive [start, end] range stepped by a whole number of days.
• ISO date age: Compute the calendar-aware elapsed years, months, and days between a birth date and an as-of date.
• ISO date business days count: Count the business days in an inclusive date range, skipping caller-supplied weekend weekdays and holidays.
• ISO date nth weekday of month: Return the date of the nth occurrence of an ISO weekday within a calendar month.
• ISO date range intersect: Compute the intersection of two inclusive [start, end] date ranges.
• ISO date compare: Compare two YYYY-MM-DD calendar dates and return -1, 0, or 1.