iso8601-millisecond-precision
ISO 8601 Millisecond Precision
Goal
When a temporal value must be represented textually, use ISO 8601.
This skill governs textual formatting and parsing only. It does not require temporal values to be stored internally as strings when the stack provides built-in or standard-library temporal types.
When the textual representation includes a time component, use millisecond precision exactly. For example, use 2026-03-20T14:35:12.123Z, not a seconds-only form and not a microsecond or nanosecond form.
For date-only values, use the ISO 8601 calendar date form such as 2026-03-20. Millisecond precision applies to temporal strings that include a time component.
What Counts as In Scope
Apply this skill to code that does one or more of these things:
- formats temporal values into strings
- parses textual date, time, datetime, or timestamp values
- defines API, event, message, or persistence contracts that use textual temporal representations
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