ISO date-time add seconds

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

Add a signed whole-second delta to a strict UTC ISO-8601 datetime.

Use when you need to: iso datetime add seconds · add seconds to utc datetime · shift iso datetime by whole seconds.

Supported

• iso datetime add seconds
• add seconds to utc datetime
• shift iso datetime by whole seconds

Not supported

• leap seconds
• time zones
• offsets other than Z
• fractional seconds
• locale
• ISO-8601 duration strings
• add months or years
• DST

Behavior

• datetime must 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.
• seconds is a canonical integer string; -0 is accepted as 0. The absolute value may have at most 12 digits excluding the sign.
• The delta is applied on the UTC millisecond timeline via Date.UTC / getUTC* (no local Date getters).
• The result is formatted YYYY-MM-DDTHH:MM:SSZ. If the result year is outside 0001-9999 the call is rejected.

Input

• datetime (string, required): min length 20; max length 20; pattern ^\d{4}-\d{2}-\d{2}T\d{2}:\d{2}:\d{2}Z$
• seconds (string, required): max length 13; pattern ^-?(0|[1-9][0-9]*)$

Output

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

Limits

• max seconds digits: 12
• min year: 1
• max year: 9999

Example

Request input:

{
  "datetime": "2026-09-11T12:00:00Z",
  "seconds": "90"
}

Response:

{
  "result": {
    "datetime": "2026-09-11T12:01:30Z"
  }
}

How to call it

MCP

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

{
  "id": "iso-datetime-add-seconds",
  "version": "1.0.0",
  "input": {
    "datetime": "2026-09-11T12:00:00Z",
    "seconds": "90"
  }
}

HTTP (no key)

curl -X POST https://computefirst.net/v1/tools/iso-datetime-add-seconds/versions/1.0.0/execute \
  -H "Content-Type: application/json" \
  -d '{"datetime":"2026-09-11T12:00:00Z","seconds":"90"}'

The machine-readable contract is at /v1/tools/iso-datetime-add-seconds/versions/1.0.0.

CLI

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

Get the client at /clients/cli/.

Related 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: Add a signed whole-year delta to a YYYY-MM-DD date, clamping the day if 29 February has no match.
• ISO date-time clamp: Clamp a strict UTC ISO-8601 datetime into an inclusive [min, max] range.
• ISO date-time diff seconds: Return the signed whole-second difference between two strict UTC ISO-8601 datetimes.
• ISO date-time truncate: Truncate a strict UTC ISO-8601 datetime toward UTC zero at day, hour, minute, or second.
• ISO date add: Add a signed whole-day delta to a strict YYYY-MM-DD calendar date.