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ISO 8601

The International Standards Organisation's standard, number 8601 is an international standard for date and time representations. It is used for all date-time representations in microformats.


For a plain-language overview of ISO 8601, we recommend the ISO 8601 summary by Markus Kuhn.


Microformats using ISO8601 include:

RFC 3339

RFC 3339 defines a profile of ISO 8601 for the use in Internet protocols and standards.

  • It explicitly excludes durations and dates before the common era.
  • The more complex formats like week numbers and ordinal day are not permitted (see RFC 3339, section 5.6).

Microformats SHOULD re-use RFC 3339, but MUST NOT be limited to it, in order to include both more human readable, yet still easily unambiguously parsable, alternatives, as well as ISO 8601 features deemed to be useful.


  • How should dates before the common era be marked up? Andy Mabbett
  • If a web page is created or edited by a non-technical human, it is unfriendly to expect them to work in ISO date format. Charles Belov

See also

Related pages