# ISO date-time diff seconds

`iso-datetime-diff-seconds` · version 1.0.0 · Dates & times (UTC, ISO 8601) · free, no key needed

Return the signed whole-second difference between two strict UTC ISO-8601 datetimes.

**Use when you need to: iso datetime diff seconds · difference between utc datetimes in seconds · utc datetime difference in seconds.**

## Supported

- iso datetime diff seconds
- difference between utc datetimes in seconds
- utc datetime difference in seconds

## Not supported

- leap seconds
- time zones
- offsets other than Z
- fractional seconds
- locale
- ISO-8601 duration strings
- calendar month or year difference
- DST

## Behavior

- start and end must each match YYYY-MM-DDTHH:MM:SSZ with zero-padded fields and a real proleptic Gregorian UTC civil time.
- Years are 0001-9999. Days are linear 86400-second POSIX days. There are no leap seconds, fractional seconds, space separators, or offsets other than Z.
- The result is the canonical integer string of end minus start in whole seconds on the UTC timeline.
- The difference is negative when end is earlier than start, and 0 when the instants are equal.

## Input

- `start` (string, required): min length 20; max length 20; pattern `^\d{4}-\d{2}-\d{2}T\d{2}:\d{2}:\d{2}Z$`
- `end` (string, required): min length 20; max length 20; pattern `^\d{4}-\d{2}-\d{2}T\d{2}:\d{2}:\d{2}Z$`

## Output

- `seconds` (string, required): pattern `^(0|-?[1-9][0-9]*)$`

## Limits

- min year: 1
- max year: 9999

## Example

Request input:

```json
{
  "start": "2026-09-11T12:00:00Z",
  "end": "2026-09-11T12:01:30Z"
}
```

Response:

```json
{
  "result": {
    "seconds": "90"
  }
}
```

## How to call it

### MCP

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

```json
{
  "id": "iso-datetime-diff-seconds",
  "version": "1.0.0",
  "input": {
    "start": "2026-09-11T12:00:00Z",
    "end": "2026-09-11T12:01:30Z"
  }
}
```

### HTTP (no key)

```sh
curl -X POST https://computefirst.net/v1/tools/iso-datetime-diff-seconds/versions/1.0.0/execute \
  -H "Content-Type: application/json" \
  -d '{"start":"2026-09-11T12:00:00Z","end":"2026-09-11T12:01:30Z"}'
```

The machine-readable contract is at [/v1/tools/iso-datetime-diff-seconds/versions/1.0.0](/v1/tools/iso-datetime-diff-seconds/versions/1.0.0).

### CLI

```sh
node cli.mjs run iso-datetime-diff-seconds 1.0.0 --input input.json --base-url https://computefirst.net
```

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

## Related tools

- [ISO date-time add seconds](/tools/iso-datetime-add-seconds): Add a signed whole-second delta to a strict UTC ISO-8601 datetime.
- [ISO date-time compare](/tools/iso-datetime-compare): Compare two strict UTC ISO-8601 datetimes and return -1, 0, or 1.
- [ISO date age](/tools/iso-date-age): Compute the calendar-aware elapsed years, months, and days between a birth date and an as-of date.
- [ISO date difference](/tools/iso-date-difference): Whole days from start to end as a canonical integer string (end - start).
- [ISO date range list](/tools/iso-date-range-list): Enumerate the dates in an inclusive [start, end] range stepped by a whole number of days.
- [ISO date weekday occurrences in range](/tools/iso-date-weekday-occurrences-in-range): List every date within an inclusive date range that falls on a given ISO weekday.