I thought it was jiff

In this section, wouldn’t be more realistic for chrono users to use timezone info around the wire instead of on the wire, rather than using Local+FixedOffset?

They do say that the difference is that chrono users would need to keep out-of-band timezone information in addition to the datetime, whereas Jiff does it in-band.

    // The serialized datetime has no time zone information,
    // so unless there is some out-of-band information saying
    // what its time zone is, we're forced to use a fixed offset:

use jiff::{ToSpan, Unit, Zoned};

fn main() -> anyhow::Result<()> {
    let now = Zoned::now().round(Unit::Minute)?.intz("Europe/Kyiv")?;
    let next_year = now.checked_add(1.year())?;
    println!("{next_year}");
    Ok(())
}

$ cargo -q r
2025-07-22T17:23:00+03:00[Europe/Kyiv]

Is the cache invalidated if system tzdata is updated?

Yes, although at present, there is a TTL. So an update may take “time” to propagate. jiff::tz::db().reset() will force the cache to be invalidated. I expect the cache invalidation logic to get tweaked as we get real experience with it.

And what effect does the answer have on the example from “Jiff supports detecting time zone offset conflicts” if both zoned datetimes used the system timezone which got updated between 1. opening 2. parsing the two zoned datetimes.

It’s hard to know precisely what you mean. But once you get a jiff::tz::TimeZone, that value is immutable: docs.rs/jiff/latest/jiff/tz/struct.TimeZone.html#…

New updates to tzdb are only observed when you do a tzdb lookup.

In this section, wouldn’t be more realistic for chrono users to use timezone info around the wire instead of on the wire, rather than using Local+FixedOffset?

That’s kinda my point. How do they do that? And does it work with chrono-tz and tzfile? And what happens if tzdb updates lead to a serialized datetime with an incorrect offset in a future update of tzdb? There are all sorts of points of failure here that Jiff will handle for you by virtue of tighter integration with tzdb as a first class concept.

The original name I wanted was gigawatt or some variation there of. :)

You should absolutely not need to handle ISO 8601 and RFC 3339 manually. They are supported via the Display and FromStr trait implementations on every main type in Jiff (Span, Zoned, Timestamp, civil::DateTime, civil::Date and civil::Time). It’s technically an implementation of a mixture of ISO 8601, RFC 3339 and RFC 9557, but the grammar is specified precisely by Temporal. See: docs.rs/jiff/latest/jiff/fmt/temporal/index.html