ISO 8601 Time Strict Validator

The API sent back PT1H30M and your parser threw. Or you posted 2026-05-10 12:00 with a space in the middle and the endpoint rejected it without saying why. Pasting the string here answers the shape question fast: green or red, updating as you type, with no button to press and nothing to configure first.

Two shapes pass. One is a full date-time, YYYY-MM-DDTHH:MM:SS, with optional fractional seconds and a mandatory offset, either Z or something like -03:00. The other is a duration starting with P, carrying years, months and days, then hours, minutes and seconds after the T. Plenty of things people expect to pass come back red: a bare 2026-05-10, local time with no offset, lowercase t or z, a decimal comma, and week durations like P1W.

The catch worth knowing: this checks shape, not calendars. The string 2026-13-45T99:99:99Z reads as valid, because month 13 and hour 99 still fit the digit pattern. A lone P with no components also passes, even though ISO requires at least one. Treat the page as a typo and mask check, and leave range validation to whatever library actually parses the value. Nothing leaves your browser.