HTTP Date Formatter

How to use

1. 1Choose Build HTTP date to convert a timestamp into header-ready strings, or Parse HTTP date to inspect an existing one.
2. 2In Build mode, pick a source (current time, a calendar date and time, a Unix timestamp, or an ISO 8601 string).
3. 3Copy the IMF-fixdate output for new headers, or grab a ready-to-paste line for Date, Expires, Last-Modified, Retry-After, or Set-Cookie Expires=.
4. 4In Parse mode, paste any HTTP-date string and see the detected format, the canonical IMF-fixdate, ISO 8601, Unix seconds and milliseconds, plus a diff against now.
5. 5Watch the warnings panel for common sender mistakes: numeric offsets, the UTC token, missing leading zeros, weekday/date mismatches, and RFC 850 two-digit years.

About this tool

HTTP Date Formatter builds and parses HTTP-date strings as defined by RFC 7231 section 7.1.1.1, the timestamp format used in the Date, Expires, Last-Modified, If-Modified-Since, If-Unmodified-Since, Retry-After (date form), and Set-Cookie Expires= header values. The spec recognizes three formats: IMF-fixdate (the modern form, e.g. Sun, 06 Nov 1994 08:49:37 GMT) which every new HTTP message MUST send; the obsolete RFC 850 form with a two-digit year; and the legacy ANSI C asctime form. Parsers MUST accept all three for backward compatibility. In Build mode, pick the source for the instant (the current browser clock, a manual date and time, a Unix timestamp in seconds, a Unix timestamp in milliseconds, or an ISO 8601 string) and the tool emits all three formats side by side with copy buttons, plus ready-to-paste header lines for Date, Expires, Last-Modified, If-Modified-Since, If-Unmodified-Since, Retry-After, and a complete Set-Cookie example with the Expires= attribute. In Parse mode, paste any HTTP-date string and the tool detects which of the three formats it is in, reports the canonical IMF-fixdate equivalent, ISO 8601 in UTC, Unix seconds, Unix milliseconds, and a human-readable diff against the current clock. It also flags the most common non-compliance issues senders produce: a numeric zone offset like +0000 instead of GMT, the literal UTC token instead of GMT, single-digit day or hour fields, fractional seconds, a missing comma after the day name, weekday names that disagree with the calendar date, and the RFC 6265 two-digit year window used to disambiguate obsolete dates. Everything runs locally in your browser, so the timestamps you build or parse are never uploaded.

Free to use. Works in your browser. No signup, no login.