Developer Tools
Paste a date or timestamp string and see whether it's valid ISO 8601 — and if it isn't, which part broke.
Checked against the ISO 8601 rules for calendar dates, times, and UTC offsets.
A valid ISO 8601 string is built from a calendar date in YYYY-MM-DD order, optionally followed by a T, a 24-hour time, and a timezone offset — either Z for UTC or an explicit +HH:MM/-HH:MM. This tool checks the structure and the offset separately, so if something's wrong it can usually tell you which part failed instead of just saying "invalid."
If you need to go the other direction — from a Unix timestamp to ISO 8601 and other formats at once — the Date Format Converter handles that. For the reasoning behind why this format is worth standardizing on, see A Developer's Guide to ISO 8601.
Related
See a date rendered in ISO 8601 alongside every other common format.
Why this format sorts and parses more safely than the rest.
Convert a valid string straight into a Unix timestamp.