What s the difference between ISO 8601 and RFC 3339 Date Formats

Question

ISO 8601 and RFC 3339 seem to be two formats that are common the web  Should I use one over the other  Is one just an extension  Do I really need to care that bad

User · Answer

You shouldn t have to care that much   RFC 3339  according to itself  is a set of standards derived from ISO 8601   There s quite a few minute differences though  and they re all outlined in RFC 3339   I could go through them all here  but you d probably do better just reading the document for yourself in the event you re worried   http   tools ietf org html rfc3339

User · Answer

There are lots of differences between ISO 8601 and RFC 3339  Here is some examples to give you an idea  2020-12-09T16 09 53 00 00 is a date time value that is compliant both both standards  2020-12-09 16 09 53 00 00 uses a space to separate the date and time  This is allowed by RFC 3339 but not allowed by ISO 8601  2020-12-09T16 09 53-00 00 has a negative sign in the time offset  This is allowed by RFC 3339 but not allowed by ISO 8601  20201209T160953Z omits the hyphens  This is allowed by ISO 8601 but not allowed by RFC 3339  ISO 8601 allows for things like ordinal dates such as 2020-344 which represents the 344th day of year 2020  RFC 3339 doesn t allow for that  For your questions   Is one just an extension   No  As shown above each standard supports syntax variations not supported by the the other standard  So one syntax is not a superset or an extension of the other   Should I use one over the other   Of course this depends on your scenario  A safe general strategy is to generate date time strings that are valid by both standards  Another good general strategy is to use an existing standard library for parsing formatting date time strings and not write custom implementations unless you are addressing a genuinely custom scenario   Do I really need to care that bad   Well  that s up to you  Most regular developers who deal with date time strings should have a high level understanding but don t need to dive into the details

User · Answer

Is one just an extension    Pretty much  yes - RFC 3339 is listed as a profile of ISO 8601   Most notably RFC 3339 specifies a complete representation of date and time  only fractional seconds are optional    The RFC also has some small  subtle differences   For example truncated representations of years with only two digits are not allowed -- RFC 3339 requires 4-digit years  and the RFC only allows a period character to be used as the decimal point for fractional seconds   The RFC also allows the  T  to be replaced by a space  or other character   while the standard only allows it to be omitted  and only when there is agreement between all parties using the representation    I wouldn t worry too much about the differences between the two  but on the off-chance your use case runs in to them  it d be worth your while taking a glance at    RFC 3339 Wikipedia entry on ISO 8601

User · Answer

RFC 3339 is mostly a profile of ISO 8601  but is actually inconsistent with it in borrowing the  -00 00  timezone specification from RFC 2822   This is described in the Wikipedia article

[datetime] What's the difference between ISO 8601 and RFC 3339 Date Formats?

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