Util Monster
Free
Display browser-recognized date/time strings such as ISO 8601 and RFC 2822, as well as Unix timestamps, in several formats. Numeric input is treated as a Unix timestamp in seconds or milliseconds according to its digit count. Choose a UTC offset to see the ISO 8601 representation at that fixed offset.
ISO 8601 is the international standard format for dates and times, e.g. "YYYY-MM-DDTHH:mm:ss.sssZ" — year-month-day and hour:minute:second separated by T, followed by UTC (Z) or a timezone offset such as +09:00. It is widely used in logs, API responses, and databases because it is unambiguous to both humans and machines.
A Unix timestamp represents seconds or milliseconds relative to 1970-01-01T00:00:00Z. This tool identifies numeric input by digit count, excluding a leading minus sign. It treats 1 to 11 digits as seconds and 12 or more as milliseconds; values outside the JavaScript Date range are invalid. When you select a fixed UTC offset, the tool adds that offset in minutes to the UTC instant, formats the result as a wall-clock time, and appends the original offset. This calculation does not depend on the browser’s local time zone.
RFC 2822 is common in email headers, and HTTP Date headers use a GMT form such as ‘Mon, 15 Jan 2024 09:30:00 GMT’. JavaScript’s toUTCString() produces an HTTP-style UTC date string. Date.parse() can recognize this form and supported ISO 8601 strings, so the tool can convert supported date strings from sources such as log files, API headers, and database dumps.