NumericDate

NumericDate is a data representation used to encode a point in time as a numeric value, most notably in security token specifications such as JSON Web Tokens (JWT). In this context, NumericDate is defined as the number of seconds that have elapsed since the Unix epoch, 1970-01-01T00:00:00Z, and is expressed as a JSON numeric value. The concept is designed to be timezone-agnostic and easily comparable across systems.

Format and semantics

The typical format for NumericDate is an integer representing whole seconds since the epoch. Some implementations may allow fractional seconds, but integers are standard in most specifications. The value 0 corresponds to the epoch itself, and larger values represent subsequent times. Because the representation is a simple scalar, it avoids locale, format, and timezone issues that accompany human-readable dates.

Usage and context

NumericDate is commonly used in token and credential systems to denote time-related claims, such as issuance time (iat), expiration time (exp), and not-before time (nbf). As a machine-friendly representation, it facilitates fast comparison and validation in authentication and authorization workflows. It is intended for computational use rather than human display; conversion to ISO 8601 or local time is performed by applications when presenting information to users.

Considerations

Producers and consumers should ensure clocks are synchronized and aware of potential clock skew. While 64-bit representations mitigate the Y2038 problem in most environments, some 32-bit contexts may overflow in the near future. RFC guidance and library support should be consulted when adopting NumericDate in a system.