Which Markdown processors preserve ISO‑8601 timestamps without timezone conversion?

Which Markdown processors preserve ISO‑8601 timestamps without timezone conversion depends on whether the processor treats the string as raw text or parses it into a temporal value. Text-passing renderers emit timestamps verbatim; tools that interpret front-matter dates as typed values may re-express them in UTC or the site timezone.

• CommonMark reference implementations emit ISO‑8601 strings unchanged, treating them as plain text.
• GitHub Flavored Markdown does not parse or convert ISO‑8601 timestamps; they appear verbatim unless nested inside GFM-specific syntax.
• Pandoc (≥2.0) passes ISO‑8601 date literals through unchanged during HTML conversion, unless a date filter or template variable is applied.
• markdown-it, in default configuration, preserves ISO‑8601 strings; only add-on date-formatting plugins alter the output.
• Jekyll (v4.x) parses front-matter dates as Ruby Time objects, applying the site's default timezone (typically UTC), so the original offset is not preserved unless the date is kept as a raw string.
• Hugo (≥0.110) converts offset-aware front-matter dates to UTC time.Time, losing the original offset unless the value is accessed as a string or the site timezone matches the offset.

These patterns reflect default, version-specific behavior and should be treated as assumptions to verify against your installed versions; custom templates, filters, or plugins can override them. On the third sub-question: a portable Markdown document conveys a regional time reliably only by embedding the explicit UTC offset in the string itself. Renderers that treat the text literally keep it intact, but any pipeline that parses the value into a date object may re-express it, so there is no guarantee once front matter is involved.

1. Create a Markdown file containing an ISO‑8601 timestamp with a non-zero offset, for example 2026-10-19T15:52:16-04:00, both in front matter and as inline text.
2. Render the file with the target processor to HTML (or plain text).
3. Compare the rendered output string to the original input; preservation is confirmed if they match exactly.
4. Inspect the rendered HTML for converted times (for example, the equivalent UTC value) to detect implicit normalization.

One diagnostic detail that would change the recommendation: which processor and version you are using, and whether the timestamp lives in front matter or inline text — the two paths behave differently.