# ISO date is leap year

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

Test whether a proleptic Gregorian calendar year is a leap year.

**Use when you need to: iso date is leap year · leap year check · is year a leap year.**

## Supported

- iso date is leap year
- leap year check
- is year a leap year

## Not supported

- Julian calendar
- lunar calendars
- timezones

## Behavior

- year is a JSON integer from 1 to 9999.
- Leap year rule: year % 4 == 0 && (year % 100 != 0 || year % 400 == 0). For example 2000 and 2024 are leap years; 1900 and 2023 are not.

## Input

- `year` (integer, required): min 1; max 9999

## Output

- `leap` (boolean, required)

## Limits

- year min: 1
- year max: 9999

## Example

Request input:

```json
{
  "year": 2024
}
```

Response:

```json
{
  "result": {
    "leap": true
  }
}
```

## How to call it

### MCP

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

```json
{
  "id": "iso-date-is-leap-year",
  "version": "1.0.0",
  "input": {
    "year": 2024
  }
}
```

### HTTP (no key)

```sh
curl -X POST https://computefirst.net/v1/tools/iso-date-is-leap-year/versions/1.0.0/execute \
  -H "Content-Type: application/json" \
  -d '{"year":2024}'
```

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

### CLI

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

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

## Related tools

- [ISO date is business day](/tools/iso-date-is-business-day): Test whether a date is a business day given caller-supplied weekend weekdays and holiday dates.
- [ISO date range contains](/tools/iso-date-range-contains): Test whether an inclusive [start, end] date range contains a given date.
- [ISO date week count in year](/tools/iso-date-week-count-in-year): Return the number of ISO-8601 weeks (52 or 53) in an ISO week-numbering year.
- [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 day of year](/tools/iso-date-day-of-year): Return the ordinal day number (1-366) of a YYYY-MM-DD date within its calendar year.
- [ISO date days in month](/tools/iso-date-days-in-month): Return the number of calendar days in a given proleptic Gregorian year and month.