ISO date previous weekday

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

Return the most recent date on or before a given date that falls on a specified ISO weekday.

Use when you need to: iso date previous weekday · last monday before date · preceding weekday.

Supported

• iso date previous weekday
• last monday before date
• preceding weekday

Not supported

• timezones
• locale weekday names
• business day skip

Behavior

• date is a strict YYYY-MM-DD proleptic Gregorian UTC calendar date with year 0001-9999.
• weekday is a JSON integer 1-7 with Monday=1 .. Sunday=7.
• inclusive is an optional boolean, default false. When true and date already falls on weekday, the result is date itself.
• Otherwise the result is the latest date strictly before date whose ISO weekday equals weekday (at most 7 days earlier).
• The call is rejected if the result would fall outside year 0001-9999.

Input

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

Output

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

Limits

• year min: 1
• year max: 9999
• max days back: 7

Example

Request input:

{
  "date": "2026-09-15",
  "weekday": 5
}

Response:

{
  "result": {
    "date": "2026-09-11"
  }
}

How to call it

MCP

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

{
  "id": "iso-date-previous-weekday",
  "version": "1.0.0",
  "input": {
    "date": "2026-09-15",
    "weekday": 5
  }
}

HTTP (no key)

curl -X POST https://computefirst.net/v1/tools/iso-date-previous-weekday/versions/1.0.0/execute \
  -H "Content-Type: application/json" \
  -d '{"date":"2026-09-15","weekday":5}'

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

CLI

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

Get the client at /clients/cli/.

Related tools

• ISO date last weekday of month: Return the date of the last occurrence of an ISO weekday within a calendar month.
• ISO date next weekday: Return the next date on or after a given date that falls on a specified ISO weekday.
• ISO date nth weekday of month: Return the date of the nth occurrence of an ISO weekday within a calendar month.
• ISO date weekday occurrences in range: List every date within an inclusive date range that falls on a given ISO weekday.
• ISO date month end: Return the last valid calendar day of the year-month of a YYYY-MM-DD date.
• ISO date to week: Convert a YYYY-MM-DD calendar date to an ISO-8601 week date.