ISO date-time compare

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

Compare two strict UTC ISO-8601 datetimes and return -1, 0, or 1.

Use when you need to: iso datetime compare · compare two utc datetimes · datetime ordering.

Supported

• iso datetime compare
• compare two utc datetimes
• datetime ordering

Not supported

• leap seconds
• time zones
• offsets other than Z
• fractional seconds
• locale

Behavior

• a and b must match YYYY-MM-DDTHH:MM:SSZ with zero-padded fields and a real proleptic Gregorian UTC civil time, years 0001-9999.
• Comparison is on the UTC millisecond timeline (Date.UTC / getUTC*, no local Date getters).
• Returns -1 if a is before b, 0 if equal, 1 if a is after b.

Input

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

Output

• comparison (one of -1, 0, 1, required)

Limits

• min year: 1
• max year: 9999

Example

Request input:

{
  "a": "2026-09-15T12:00:00Z",
  "b": "2026-09-15T12:00:01Z"
}

Response:

{
  "result": {
    "comparison": -1
  }
}

How to call it

MCP

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

{
  "id": "iso-datetime-compare",
  "version": "1.0.0",
  "input": {
    "a": "2026-09-15T12:00:00Z",
    "b": "2026-09-15T12:00:01Z"
  }
}

HTTP (no key)

curl -X POST https://computefirst.net/v1/tools/iso-datetime-compare/versions/1.0.0/execute \
  -H "Content-Type: application/json" \
  -d '{"a":"2026-09-15T12:00:00Z","b":"2026-09-15T12:00:01Z"}'

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

CLI

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

Get the client at /clients/cli/.

Related tools

• ISO date compare: Compare two YYYY-MM-DD calendar dates and return -1, 0, or 1.
• ISO date-time diff seconds: Return the signed whole-second difference between two strict UTC ISO-8601 datetimes.
• ISO date-time add seconds: Add a signed whole-second delta to a strict UTC ISO-8601 datetime.
• ISO date-time clamp: Clamp a strict UTC ISO-8601 datetime into an inclusive [min, max] range.
• ISO date-time truncate: Truncate a strict UTC ISO-8601 datetime toward UTC zero at day, hour, minute, or second.
• Duration compare: Compare two SI duration amounts after converting both to nanoseconds.