# ISO week to date

`iso-week-to-date` · version 1.0.0 · Dates & times (UTC, ISO 8601) · free, no key needed

Convert an ISO-8601 week date to a YYYY-MM-DD calendar date.

**Use when you need to: iso week to date · convert iso week date to calendar date · calendar date from iso week.**

## Supported

- iso week to date
- convert iso week date to calendar date
- calendar date from iso week

## Not supported

- locale week numbers
- Sunday-first weeks
- ISO ordinal dates
- timezones
- datetime output
- fiscal weeks

## Behavior

- year, week, and weekday are JSON integers that pass Number.isInteger.
- year is 1-9999, week is 1-53, and weekday is 1-7 with Monday=1 and Sunday=7.
- Week 53 is rejected when that ISO year has only 52 weeks.
- Combinations whose calendar date would fall outside years 0001-9999 are rejected.
- Output date is a zero-padded YYYY-MM-DD calendar date.

## Input

- `year` (integer, required): min 1; max 9999
- `week` (integer, required): min 1; max 53
- `weekday` (integer, required): min 1; max 7

## Output

- `date` (string, required): min length 10; max length 10; pattern `^\d{4}-\d{2}-\d{2}$`

## Limits

- year min: 1
- year max: 9999
- week min: 1
- week max: 53
- weekday min: 1
- weekday max: 7

## Example

Request input:

```json
{
  "year": 2026,
  "week": 2,
  "weekday": 4
}
```

Response:

```json
{
  "result": {
    "date": "2026-01-08"
  }
}
```

## How to call it

### MCP

Connect `https://computefirst.net/mcp` ([setup](/docs#connect)), then call `execute` with:

```json
{
  "id": "iso-week-to-date",
  "version": "1.0.0",
  "input": {
    "year": 2026,
    "week": 2,
    "weekday": 4
  }
}
```

### HTTP (no key)

```sh
curl -X POST https://computefirst.net/v1/tools/iso-week-to-date/versions/1.0.0/execute \
  -H "Content-Type: application/json" \
  -d '{"year":2026,"week":2,"weekday":4}'
```

The machine-readable contract is at [/v1/tools/iso-week-to-date/versions/1.0.0](/v1/tools/iso-week-to-date/versions/1.0.0).

### CLI

```sh
node cli.mjs run iso-week-to-date 1.0.0 --input input.json --base-url https://computefirst.net
```

Get the client at [/clients/cli/](/clients/cli/).

## Related tools

- [ISO date to week](/tools/iso-date-to-week): Convert a YYYY-MM-DD calendar date to an ISO-8601 week date.
- [ISO date add months](/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](/tools/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 from day of year](/tools/iso-date-from-day-of-year): Convert a calendar year and ordinal day number (1-366) to a YYYY-MM-DD date.
- [ISO date range split by month](/tools/iso-date-range-split-by-month): Split an inclusive [start, end] date range into per-calendar-month sub-ranges.
- [ISO date add](/tools/iso-date-add): Add a signed whole-day delta to a strict YYYY-MM-DD calendar date.