jiff

This release fixes a bug in duration parsing where, e.g., -PT0.5S would be parsed as if the - sign didn't exist. This bug also affects friendly durations such as -0.5s.

Bug fixes:

• #613: Fixes a bug where the sign in a duration could be ignored while parsing.

This release contains a few small enhancements. Namely, some error messages for parsing datetime values have been improved by removing some redundant messaging. Additionally, the strftime APIs on datetime values can no longer panic. Instead, they'll silently pass through invalid formatting directives.

Enhancements:

• #519: Improve some parsing error messages by removing redundancy.
• #585: Change Timestamp::strftime (and similar methods) so that they will never panic.

This release permits the use of a global time zone database in alloc-only environments. It also contains a massive internal refactor that introduces a new jiff-core crate for better code sharing.

Enhancements:

• #285: Decouple naming of time zones from their TZif data.
• #373: Add a new jiff-core crate for better code sharing.
• #533: A bundled TimeZoneDatabase is now available when only alloc is enabled.

This release updates Jiff's bundled copy of the [IANA Time Zone Database] to 2026c. See the 2026c release announcement for more details.

This release fixes a minor bug in tests that prevents the crate from running through standard build processes in Linux distributions downstream.

• #594: Fix imports in recently added tests.

This release fixes a safety soundness bug in Jiff's lower level printing APIs. There is also a nice performance improvement to civil::Date::weekday, which also improves downstread routines like civil::Date::nth_weekday and datetime<-->timestamp conversions in some cases.

Enhancements:

• #591: Improve the performance of weekday calculations from Gregorian dates by 30-50%.

Bug fixes:

• #592: Fix safety soundness bug when using a non-empty String destination buffer with lower level printing APIs inside of jiff::fmt.

This release adds support for [defmt], which is a highly efficient logging framework that targets resource-constrained devices, like microcontrollers.

Enhancements:

• #505: Add support for the defmt crate by implementing defmt::Format on the principle public types in Jiff.
• #584: Add Zoned::UNIX_EPOCH as a constant.
• #587: Change the Debug output for civil::ISOWeekDate to match the Debug output style of other primitive datetime types.

Bug fixes:

• #525: Fix a bug that prevented time zone lookups when using an on-disk time zone database on Windows.
• #539: Fix a bug where rendering a datetime in an error message would omit a T separator.

This is a small release with a fix for test failures on 32-bit targets in no-alloc environments.

Bug fixes:

• #573: Fix test failure on 32-bit targets in no-alloc environments.

This is a small release with a bug fix for build errors on Windows for very old versions of Rust.

Bug fixes:

• #566: Fix build error on Windows for very old versions of Rust (e.g., 1.71).

This release has a couple enhancements.

Firstly, Jiff now uses windows-link for calling FFI routines on Windows instead of windows-sys. Using windows-link means less churn and fewer duplicates in the dependency graph.

Secondly, a new jiff-sqlx 0.2.0 release has been put out to support sqlx 0.9.0.

Enhancements:

• #538: Replace use of windows-sys with windows-link and inline bindings.
• #561: Update jiff-sqlx to use sqlx 0.9.0 and release jiff-sqlx 0.2.0.

Bug fixes:

• #548: Absolutetize incorrect relative size terms in the documentation of RoundMode.

This release updates Jiff's bundled copy of the [IANA Time Zone Database] to 2026b. See the 2026b release announcement for more details.

This release primarily adds a new memory_usage routine for reporting heap allocation sizes for the TimeZone and Zoned types. This release also acknowledges and updates the timeline expectations for a Jiff 1.0 release in README.md.

Enhancements:

• #520: Add memory_usage to the TimeZone and Zoned types.
• #535: Improve comment in Span::checked_add example.

Bug fixes:

• #541: Update Jiff 1.0 timeline.

This release updates Jiff's bundled copy of the [IANA Time Zone Database] to 2026a. See the 2026a release announcement for more details.

This release includes a bug fix where fallible conversions from signed durations to unsigned durations could panic in some cases.

Bug fixes:

• #526: Fix a panicking bug that occurs for std::time::Duration::try_from(SignedDuration::new(0, -1)).

This release contains a performance improvement and a bug fix for civil::Date::new where it could panic on some inputs.

Bug fixes:

• #523: Fix a bug where Date::new could panic. This was a regression introduced in jiff 0.2.20.

Performance:

• #518: Improve Timestamp to civil::DateTime conversion performance by ~15%.

This release contains a major internal refactor that moves off of using ranged integers internally. There are also some small bug fixes and added support for finding the system time zone on emscripten targets.

Enhancements:

• #11: Stop using ranged integers internally.
• #490: Add support for retrieving the system time zone on emscripten targets.
• #500: Update comparison with the time crate in the Jiff documentation.
• #502: Enable some non-default features for the Rust Playground deployment.

Bug fixes:

• #485: Fix bug with padding for negative integers in strftime.
• #486: Make %^c result in uppercase strings where appropriate.

This is a small release with a performance optimization (with respect to doing heavily contended arithmetic on Zoned values) and a bug fix for a panic that can occur when using %2s in strftime.

Enhancements:

• #491: Avoid cloning TimeZone for consuming operations on Zoned.

Bug fixes:

• #497: Fix a panic in timestamp.strftime("%2s").

This release ships a sizeable refactor to the RFC 2822, RFC 9110, RC 3339, RFC 9557, ISO 8601 and friendly format printers. Specifically, they are now all monomorphic internally (instead of being generic over jiff::fmt::Write) and write to uninitialized buffers. This improves runtime performance (sometimes dramatically so), and to a more modest degree, decreases binary size and improves compile times.

This release also includes a bug fix where DateTime::MIN.to_zoned(..) could panic.

Enhancements:

• #460: Improve runtime performance and binary size of RFC 2822 printer.
• #461: Tweak behavior of printing min/max offsets in RFC 2822 and Temporal printers.
• #462: Export fallible constructors for jiff::SignedDuration.
• #465: Improve runtime performance and binary size of the "friendly" duration printer.
• #468: Improve runtime performance and binary size of the Temporal ISO 8601 duration printer.
• #470: Improve runtime performance and binary size of the Temporal ISO 8601 datetime printer.
• #474: Improve runtime performance and binary size of Jiff's strftime implementation.
• #477: Fix a bug where time zone lookups for civil::DateTime::MIN could panic.

This release contains binary size improvements to Jiff, more succinct error messages and some new minor APIs.

While Jiff 1.0 is overdue, I've been doing a lot of experimenting with improving Jiff's binary size and compile times. In particular, I want to spend time doing this before Jiff 1.0 so that we don't box ourselves into a corner. (For example, some binary size improvements may require minor API breaking changes.)

In this release, Jiff has switched to structured error handling internally in an effort to provide error predicates and also hopefully improve binary sizes and compile times. Overall this didn't have as big of an impact on binary sizes or compile times as I was hoping. I did take this opportunity to make Jiff's error messages a bit more succinct. In many cases, this involved de-duplicating some aspects of error messages and omitting user provided input in the messages. If you feel like there is a significant decrease in error message quality that isn't easily amended by callers providing additional context themselves, please open an issue.

This release also updates Jiff's bundled copy of the [IANA Time Zone Database] to 2025c. See the 2025c release announcement for more details.

Enhancements:

• #412: Add Display, FromStr, Serialize and Deserialize trait implementations for jiff::civil::ISOWeekDate. These all use the ISO 8601 week date format.
• #418: Add some basic predicates to jiff::Error for basic error introspection.
• #453, #454: Switch to structured error handling internally.
• #456, #457, #458: Various improvements to binary size.

This release contains a number of enhancements and bug fixes that have accrued over the last few months. Most are small polishes. A couple of the bug fixes apply to panics that could occur when parsing invalid TZ strings or invalid strptime format strings.

Also, parsing into a Span should now be much faster (for both the ISO 8601 and "friendly" duration formats).

Enhancements:

• #298: Add Serde helpers for (de)serializing std::time::Duration values.
• #396: Add Sub and Add trait implementations for Zoned (in addition to the already existing trait implementations for &Zoned).
• #397: Add BrokenDownTime::set_meridiem and ensure it overrides the hour when formatting.
• #409: Switch dependency on serde to serde_core. This should help speed up compilation times in some cases.
• #430: Add new Zoned::series API, making it consistent with the same API on other datetime types.
• #432: When lenient mode is enabled for strftime, Jiff will no longer error when the formatting string contains invalid UTF-8.
• #432: Formatting of %y and %g no longer fails based on the specific year value.
• #432: Parsing of %s is now a bit more consistent with other fields. Moreover, BrokenDownTime::{to_timestamp,to_zoned} will now prefer timestamps parsed with %s over any other fields that have been parsed.
• #433: Allow parsing just a %s into a Zoned via the Etc/Unknown time zone.

Bug fixes:

• #386: Fix a bug where 2087-12-31T23:00:00Z in the Africa/Casablanca time zone could not be round-tripped (because its offset was calculated incorrectly as a result of not handling "permanent DST" POSIX time zones).
• #407: Fix a panic that occurred when parsing an empty string as a POSIX time zone.
• #410: Fix a panic that could occur when parsing %: via strptime APIs.
• #414: Update some parts of the documentation to indicate that TimeZone::unknown() is a fallback for TimeZone::system() (instead of the jiff 0.1 behavior of using TimeZone::UTC).
• #423: Fix a panicking bug when reading malformed TZif data.
• #426: Fix a panicking bug when parsing century (%C) via strptime.
• #445: Fixed bugs with parsing durations like -9223372036854775808s and -PT9223372036854775808S.

Performance:

• #445: Parsing into Span or SignedDuration is now a fair bit faster in some cases.

This release fixes a bug where error values were being constructed during parsing even in the success case. This was a regression introduced in 0.2.14 as a result of trying to improve compilation times. Thankfully, fixing this regression doesn't seem to meaningfully impact the amount of IR generated by compiling Jiff.

Bug fixes:

• #385: Fixes a performance regression for parsing.

This release includes a smattering of bug fixes, and hopefully a small improvement to the time it takes to compile Jiff. Also, in this release, when TZ is set to a non-empty but invalid value, Jiff will always fall back to Etc/Unknown when using TimeZone::system(). This differs from previous behavior where Jiff would, in this case, attempt to read the system's default time zone. This change brings Jiff into consistency with existing Unix tooling like date, and is also arguably a better failure mode. That is, when TZ is set but invalid, we shouldn't silently fall back to the default system time zone, but instead do something that indicates something has potentially gone wrong.

Enhancements:

• #364: Jiff now falls back to Etc/Unknown for invalid TZ values.
• #379: Improve compilation times.

Bug fixes:

• #365: Fixes a compile error in Jiff when only the tzdb-concatenated feature was enabled.
• #366: Fixes slow initial Zoned::now() in environments where /usr/share/zoneinfo is on a very slow file system (like CI environments).
• #376: Avoids searching for a tzdb at /usr/share/zoneinfo on Windows.

This release fixes a bug in a corner case where TimeZone::following could sometimes omit the last time zone transition. This could only happen in time zones that once had daylight saving time, but ended it. This did not have an impact on other Jiff APIs that handle daylight saving time.

Bug fixes:

• #362: Fix a bug where TimeZone::following could omit the last historical time zone transition.

This release fixes a couple bugs in Jiff's parser. In particular, a regression was introduced in jiff 0.2.11 where its RFC 2822 parser could panic on some inputs. Previous releases of Jiff are unaffected.

Bug fixes:

• #357: Fix a bug where parsing 1970-06-01T00-00:45:00[Africa/Monrovia] succeeded but it should fail.
• #359: Fix a bug where the RFC 2822 parser could panic on some inputs.

This release includes new APIs for customizing Jiff's strtime behavior along with a few minor bug fixes. Jiff's strtime formatting API has also been optimized. It's about twice as fast as it was.

This release also coincides with the publication of jiff-icu 0.2.0-beta.2, which has support for icu 2.0.0-beta.2.

Enhancements:

• #338: Add support for the %c, %r, %X and %x conversion specifiers.
• #341: Add support for %q in jiff::fmt::strtime (prints quarter of year).
• #342: Add support for %::z and %:::z in jiff::fmt::strtime.
• #344: Add support for %N in jiff::fmt::strtime (alias for %9f).
• #350: Add a "lenient" mode for strtime formatting APIs that ignores most errors.

Bug fixes:

• #328: Document default precision behavior of Display impls for datetime types.
• #340: Allow whitespace in more places in RFC 2822 parser (improves spec compliance).
• #346: TimeZone::get("UTC") should now always return TimeZone::UTC.

Performance:

• #338: Jiff's strftime APIs are now approximately twice as fast as they were. Performance should be comparable to chrono and time's prebuilt APIs.

This release includes a bug fix for parsing Tuesday when using %A via Jiff's strptime APIs. Specifically, it would recognize Tueday instead of Tuesday.

Bug fixes:

• #333: Fix typo in strptime parsing from Tueday to Tuesday.

This release includes a bug fix that, in debug mode, could result in datetime types having different hashes for the same value. This could cause problems, for example, if you are using datetimes as keys in a hash map. This problem didn't exist when Jiff was compiled in release mode.

This release also improves the panic message shown when the js feature isn't enabled and the current time is requested on wasm32-unknown-unknown targets.

Enhancements:

• #296: Provide a better panic message when Zoned::now() fails on WASM.

Bug fixes:

• #330: Fix bug where Hash on datetime types could yield different hash values for the same underlying date/time.

This release fixes a bug where the constructors on SignedDuration for floating point durations could panic (in debug mode) or produce incorrect results (in release mode). This bug only impacts users of the try_from_secs_{f32,f64} and from_secs_{f32,f64} methods on SignedDuration.

Enhancements:

• #326: Add an alternate Debug impl for SignedDuration that only shows its second and nanosecond components (while using only one component when the other is zero).

Bug fixes:

• #324: Fix a bug that could produce a panic or incorrect results in SignedDuration::(try_)?from_secs_{f32,f64}.

This release includes a bug fix that changes how an empty but set TZ environment variable is interpreted (as indistinguishable from TZ=UTC). This also includes a new enabled by default create feature, perf-inline, which allows toggling Jiff's use of inline(always). This may help improve compile times or decrease binary size.

Enhancements:

• #320: Remove some internal uses of generics to mildly improve compile times.
• #321: Add perf-inline crate feature for controlling inline(always) annotations.

Bug fixes:

• #311: Make TZ= indistinguishable from TZ=UTC.

This release includes a few bug fixes and support for discovering the IANA Time Zone Database automatically on Illumos.

Enhancements:

• #315: Add support for automatically finding the tzdb on Illumos.

Bug fixes:

• #305: Fixed Zoned rounding on days with DST time zone transitions.
• #309: Fixed bug where TimeZone::preceding could omit historical time zone transitions for time zones that have eliminated DST in the present.
• #312: Fixed nth_weekday_in_month, where it would sometimes incorrectly return an error.

This release updates Jiff's bundled copy of the [IANA Time Zone Database] to 2025b. See the 2025b release announcement for more details.

Enhancements:

• #300: Update jiff-tzdb to 2025b.

This is another small release that fixes a problem where Jiff could break builds if they relied on inference for integer comparisons. Specifically, Jiff uses internal trait impls to make comparing its internal ranged integers more convenient. But Rust the language has no concept of "internal" trait impls, and thus this can impact type inference. If code was written in a way that relies on a singular trait impl that is available, then adding Jiff to the project can cause it to break.

This isn't arguably Jiff's fault per se, but since these trait impls were just about internal convenience and not essential to Jiff's design, we adopt a pragmatic approach and just remove them.

Bug fixes:

• #293: Remove internal trait impls that can cause breaks due to inference failures.

This is a small release that fixes a bug in the handling of POSIX time zones in some cases. Specifically, the implementation of Date::yesterday was wrong when the date was the first of the month. This was a regression introduced in 0.2.2 and was not present in older releases. More test coverage has been added.

Bug fixes:

• #290: Fix bug in implementation of Date::yesterday.

This release of Jiff includes a new opt-in proc macro for embedding a TimeZone into your binary. Just enable Jiff's static feature, and this will print the current time in the America/New_York time zone:

use jiff::{
    tz::{self, TimeZone},
    Timestamp,
};

fn main() {
    static TZ: TimeZone = tz::get!("America/New_York");
    let zdt = Timestamp::now().to_zoned(TZ.clone());
    println!("{zdt}");
}

This enables TimeZone to be meaningfully used in core-only environments, even when dynamic memory allocation isn't available.

This release also features a number of performance improvements for time zone lookups. In some cases, the improvement is significant (by an order of magnitude).

Additionally, the IANA Time Zone Database embedded into jiff-tzdb now uses "rearguard" semantics. This means that the boolean flag indicating whether daylight saving time is active or not (only accessible via TimeZone::to_offset_info) will respect the actual definition of daylight saving time. (This is relevant, for example, for time zones like Europe/Dublin, where their summer time is legally known as their standard time, but is in effect daylight saving time.)

Enhancements:

• #256: Add tz::{get,include} macros for time zone support in core-only environments.
• #258: Switch to rearguard tzdb data in jiff-tzdb and document it.
• #259: De-duplicate TZif data in jiff-tzdb.
• #273: Add "crate features" documentation to jiff-sqlx and jiff-diesel.
• #277: Document semver guarantee for error conditions on Timestamp constructors.
• #277: Greatly optimize time zone lookups (for both timestamps and civil datetimes).

Bug fixes:

• #261: Improve the documentation for ZonedWith::nanosecond and ZonedWith::subsec_nanosecond.

This release includes a massive number of optimizations that significantly improves performance in some cases. If you had a workload whose performance with Jiff was underwhelming, please give it a try. I welcome questions via [Discussions on GitHub].

This release also provides a new API, Timestamp::constant, for constructing Timestamp values in a const context.

Enhancements:

• #235, #255, #266: A massive number of performance improvements. Jiff should now generally be faster than chrono and time.
• #263: Add Timestamp::constant for constructing timestamps in const context.

This is a new semver incompatible release of Jiff. It contains several breaking changes. I expect most users of Jiff to be able to upgrade without any changes. The fundamental API organization of Jiff has not changed.

Some of the highlights of this release include reducing footguns and better ecosystem integration.

For reducing footguns, APIs on Span will no longer implicitly assume that days are always 24 hours long. And Span no longer implements PartialEq or Eq (instead favoring span.fieldwise() to create a value that supports naive fieldwise comparison). Moreover, when using TimeZone::system() (perhaps via Zoned::now()), if the system time zone could not be detected, then a special Etc/Unknown time zone will be used instead. This avoids erroring, but also surfaces itself to make it clearer that something has (perhaps) gone wrong.

As for ecosystem integration, this release coincides with the publication of the [jiff-icu], [jiff-sqlx] and [jiff-diesel] crates. jiff-icu integrates with the [ICU4X project], and is now the recommended way to use Jiff to work with non-Gregorian calendars or to localize datetimes for end users. jiff-sqlx and jiff-diesel provide wrapper types that implement the necessary traits to make it ergonomic to store and retrieve Jiff values in a database using [SQLx] or [Diesel], respectively.

Unless something unexpected happens, my plan is for the next breaking change release to be Jiff 1.0 in about 6 months. Once Jiff 1.0 is out, I plan to commit to it indefinitely.

BREAKING CHANGES:

This is an exhaustive list of breaking changes. Changes with the bolded RUNTIME prefix are changes that will not be caught by the Rust compiler. That is, they are changes in runtime behavior.

• #28: The deprecated intz routines on Zoned, Timestamp, civil::DateTime and civil::Date have been removed. You can use in_tz instead. This change was made because many found the name intz to be unclear.
• #32: The PartialEq and Eq trait implementations on Span have been removed. Ideally these shouldn't have been used, but if you do need them, please use Span::fieldwise to create a SpanFieldwise, which does have the PartialEq and Eq traits implemented. These were removed on Span itself because they made it very easy to commit subtle bugs.
• #36: Turn panics during Timestamp::saturing_add into errors. Callers adding spans that are known to contain units of hours or smaller are guaranteed that this will not return an error.
• RUNTIME #48: On Span APIs, days are no longer silently assumed to always be 24 hours when a relative datetime is not provided. Instead, to perform operations on units of days or bigger, callers must either provide a relative date or opt into invariant 24-hour days with SpanRelativeTo::days_are_24_hours. Shortcuts have been added to the span builders. For example, SpanTotal::days_are_24_hours.
• RUNTIME #147: Change the behavior of the deprecated %V conversion specifier in jiff::fmt::strtime from formatting an IANA time zone identifier to formatting an ISO 8601 week number. To format an IANA time zone identifier, use %Q or %:Q (which were introduced in jiff 0.1).
• RUNTIME #212: When parsing into a Zoned with a civil time corresponding to a gap, we treat all offsets as invalid and return an error. Previously, we would accept the offset as given. This brings us into line with Temporal's behavior. For example, previously Jiff accepted 2006-04-02T02:30-05[America/Indiana/Vevay] but will now return an error. This is desirable for cases where a datetime in the future is serialized before a change in the daylight saving time rules. For more examples, see jiff::fmt::temporal::DateTimeParser::offset_conflict for details on how to change Jiff's default behavior. This behavior change also applies to tz::OffsetConflict::PreferOffset.
• RUNTIME #213: Tweak the semantics of tz::TimeZoneDatabase so that it only initializes one internal tzdb instead of trying to find as many as possible. It is unlikely that you'll be impacted by this change, but it's meant to make the semantics be a bit more sensible. (In jiff 0.1, it was in theory possible for one tz lookup to succeed in the system zoneinfo and then another tz lookup to fail in zoneinfo but succeed automatically via the bundled copy. But this seems confusing and possibly not desirable. Hence the change.)
• #218: In order to make naming a little more consistent between Zoned and civil::Date, the civil::Date::to_iso_week_date and civil::ISOWeekDate::to_date APIs were renamed to civil::Date::iso_week_date and civil::ISOWeekDate::date.
• #220: Remove Span::to_duration for converting a Span to a std::time::Duration and rename Span::to_jiff_duration to Span::to_duration. This prioritizes SignedDuration as the "primary" non-calendar duration type in Jiff. And makes it more consistent with APIs like Zoned::duration_since. For non-calendar spans, the TryFrom<Span> for std::time::Duration still exists. For calendar durations, use Span::to_duration and then convert the SignedDuration to std::time::Duration. Additionally, Timestamp::from_jiff_duration and Timestamp::as_jiff_duration were renamed to Timestamp::from_duration and Timestamp::as_duration, respectively. The old deprecated routines on the unsigned std::time::Duration have been removed.
• #221: Change the type of the value yielded by the jiff::tz::TimeZoneNameIter iterator from String to jiff::tz::TimeZoneName. This opaque type is more API evolution friendly. To access the string, either use TimeZoneName's Display trait implementation, or its as_str method.
• #222: Split TimeZone::to_offset into two methods. One that just returns the offset, and another, TimeZone::to_offset_info, which includes the offset, DST status and time zone abbreviation. The extra info is rarely needed and is sometimes more costly to compute. Also, make the lifetime of the time zone abbreviation returned by TimeZoneTransition::abbreviation tied to the transition instead of the time zone (for future API flexibility, likely in core-only environments). This change was overall motivated by wanting to do less work in the common case (where we only need the offset), and for reducing the size of a TimeZone considerably in core-only environments. Callers previously using TimeZone::to_offset to get DST status and time zone abbreviation should now use TimeZone::to_offset_info.
• RUNTIME #230: When TimeZone::system() cannot find a system configured time zone, jiff 0.1 would automatically fall back to TimeZone::UTC (with a WARN-level log message). In jiff 0.2, the fall back is now to TimeZone::unknown(), which has a special Etc/Unknown identifier (as specified by Unicode and reserved by the IANA time zone database). The fallback otherwise still behaves as if it were TimeZone::UTC. This helps surface error conditions related to finding the system time zone without causing unrecoverable failure.

Enhancements:

• #136: When the special SpanRelativeTo::days_are_24_hours() marker is used, weeks will also be treated as invariant. That is, seven 24-hour days. In all cases, working with years and months still requires a relative date.
• #228: It is now possible to forcefully use a bundled copy of the IANA time zone database without relying on disabling crate features. This can be done by enabling the tzdb-bundle-always crate feature and explicitly creating a jiff::tz::TimeZoneDatabase::bundled() database. Once in hand, you must use APIs like TimeZoneDatabase::get to create a TimeZone and avoid any APIs that implicitly use the global time zone database (like Timestamp::in_tz or even Zoned::from_str).
• #238: Add integration with the ICU4X project via the [jiff-icu] crate. jiff-icu provides traits for easily converting between datetime types defined in Jiff and datetime types defined in ICU4X.
• #240: Add integration with the SQLx project via the [jiff-sqlx] crate. jiff-sqlx provides wrapper types that implement the necessary traits in SQLx for reasonably ergonomic integration. This includes PostgreSQL and SQLite support, but not MySQL support. (It's not clear if it's possible at present to provide MySQL support for SQLx for datetime types outside of SQLx itself.)
• #241: Add integration with the Diesel project via the [jiff-diesel] crate. jiff-diesel provides wrapper types that implement the necessary traits in Diesel for reasonably ergonomic integration. This includes MySQL, PostgreSQL and SQLite support.

This release includes a few small enhancements and a bug fix. In particular, there is now Serde support for TimeZone and the ISOWeekDate API has been filled out a bit more.

Unless a serious issue is uncovered, my plan is that this will be the last release before jiff 0.2.

Enhancements:

• #89: Opt-in support for using Serde with jiff::tz::TimeZone has been added.
• #227: The civil::ISOWeekDate API has been beefed up with a few convenience methods.
• #233: Add tz::Offset::round for rounding time zone offsets.

Bug fixes:

• #231: Use more flexible offset equality when parsing offsets with fractional minutes.

This is a small release that just removes the dev-dependency on serde_yml. It has been replaced with the deprecated serde_yaml. See this post about serde_yml shenanigans for why this was done. Note that this was only a dev-dependency and thus doesn't impact folks using Jiff.

Bug fixes:

• #225: Remove dependency on serde_yml in favor of serde_yaml.

This is a small release with a bug fix for precision loss in some cases when doing arithmetic on Timestamp or Zoned.

Bug fixes:

• #223: Fix the check for fractional seconds before taking the fast path.

This is a small release with another deprecation and a new API for doing prefix parsing via strptime. There's also a bug fix for a corner case when dealing with daylight saving time gaps with the Zoned::with API.

Deprecations:

• #210: Deprecate ISOWeekDate::to_date in favor of ISOWeekDate::date.

Enhancements:

• #209: Add fmt::strtime::BrokenDownTime::parse_prefix for parsing only a prefix.

Bug fixes:

• #211: Fix unintuitive behavior of Zoned::with when time falls in a DST gap.

This release contains a number of deprecations in preparation for a jiff 0.2 release. The deprecations are meant to facilitate a smoother transition. The deprecations, when possible, come with new APIs that will permit users to write forward compatible code that will work in both jiff 0.1 and jiff 0.2.

This release also includes a handful of new conversion specifiers in Jiff's strftime and strptime APIs. This improves compatibility with the analogous implementation with GNU libc.

Deprecations:

• #28: The intz methods on Zoned, Timestamp, civil::DateTime and civil::Date have been deprecated in favor of in_tz.
• #32: The Eq and PartialEq trait implementations on Span have been deprecated in favor of using the new SpanFieldwise type.
• #48: Silently assuming days are always 24 hours in some Span APIs has now been deprecated. This will become an error in jiff 0.2. To continue assuming days are 24 hours without a relative reference date, you can use the new SpanRelativeTo::days_are_24_hours API. In jiff 0.1, you'll seen a WARN-level log message emitted if you're code will be broken by jiff 0.2.
• #147: Both %V and %:V have been deprecated in favor of %Q and %:Q. In jiff 0.2, %V will correspond to the ISO 8601 week number and %:V will result in an error. This change was made to improve compatibility with other strtime implementations. %V and %:V continue to correspond to IANA time zone identifiers in jiff 0.1, but using them for parsing or formatting will result in a WARN-level deprecation message.

Enhancements:

• #147: Adds a number of new conversion specifiers to Jiff's strftime and strptime APIs. Specifically, %C, %G, %g, %j, %k, %l, %n, %R, %s, %t, %U, %u, %W, %w. Their behavior should match the corresponding specifiers in GNU libc.

This release updates Jiff's bundled copy of the [IANA Time Zone Database] to 2025a. See the 2025a release announcement for more details.

Enhancements:

• #206: Update jiff-tzdb to 2025a.

This release includes some bug fixes, particularly for compilation on aarch64-linux-android. There are also some minor enhancements, such as making Zoned::iso_week_date a convenience function for civil::Date::iso_week_date, in line with similar functions.

My current plan is to make a reasonably quick transition to jiff 0.2 with a few pending breaking changes. I will be making some jiff 0.1 releases with deprecations in order to make the transition as smooth as possible. If all goes well with jiff 0.2, then my plan is still to do a Jiff 1.0 release in the Summer of 2025.

Deprecations:

• #197: Date::to_iso_week_date has been deprecated in favor of Date::iso_week_date.

Enhancements:

• #196: Improve ISO week date documentation regarding weekday offsets.
• #197: Add Zoned::iso_week_date, DateTime::iso_week_date and Date::iso_week_date.

Bug fixes:

• #200: Fix compilation failure on Android in a Termux shell.
• #202: Re-add license files to crate artifact.

This release adds support for Android. This support means that Jiff will automatically read its special concatenated time zone database, and will read the persist.sys.timezone property to determine the system's current time zone.

See [PLATFORM] for more specific information about Android support.

Note that this release also removed all non-essential files (including tests and test data) for the artifact uploaded to crates.io. If you need or want these files, please open a new issue.

Enhancements:

• #140: Add support for the Android platform.

This release includes a new API for setting the unit designator label in a friendly formatted duration for zero-length durations.

Enhancements:

• #192: Add option to the friendly printer for setting the unit when writing a zero-length duration.

This release includes a new type, Pieces, in the jiff::fmt::temporal sub-module. This exposes the individual components of a parsed Temporal ISO 8601 datetime string. It allows users of Jiff to circumvent the checks in the higher level parsing routines that prevent you from shooting yourself in the foot.

For example, parsing into a Zoned will return an error for raw RFC 3339 timestamps like 2025-01-03T22:03-05 because there is no time zone annotation. Without a time zone, Jiff cannot do time zone aware arithmetic and rounding. Instead, such a datetime can only be parsed into a Timestamp. This lower level Pieces API now permits users of Jiff to parse this string into its component parts and assemble it into a Zoned if they so choose.

Enhancements:

• #188: Add fmt::temporal::Pieces for granular datetime parsing and formatting.

This releases includes a UTF-8 related bug fix and a few enhancements.

Firstly, a Span's default Display implementation now writes uppercase unit designator labels. That means you'll get P1Y2M3DT4H5M6S instead of P1y2m3dT4h5m6s by default. You can restore previous behavior via jiff::fmt::temporal::SpanPrinter::lowercase. This change was made to improve interoperability.

Secondly, SignedDuration now supports rounding via SignedDuration::round. Note that it only supports rounding time units (hours or smaller). In order to round with calendar units, you'll still need to use a Span.

Enhancements:

• #130: Document value ranges for methods like year, day, hour and so on.
• #187: Add a rounding API (for time units only) on SignedDuration.
• #190: Span and SignedDuration now use uppercase unit designator labels in their default ISO 8601 Display implementation.

Bug fixes:

• #155: Relax strftime format strings from ASCII-only to all of UTF-8.

This release includes a few minor enhancements. Namely, the ability to iterate over time zone transitions (in the future or the past), and some improvements to failure modes when Timestamp and Span arithmetic fails.

Enhancements:

• #144: Add APIs for iterating over the transitions of a time zone.
• #145: Improve docs and error messages around fallible Timestamp arithmetic.

This release enhances Jiff's support for no_std environments by making its alloc feature optional. When alloc is disabled, only fixed offset time zones are supported and error messages are significantly degraded. If you have core-only use cases for Jiff, I'd love to hear about them on the issue tracker.

Enhancements:

• #162: Support platforms that do not have atomics in std.
• #168: Jiff now supports disabling the alloc feature, which enables core-only mode.
• #169: Add TimeZone::to_fixed_offset for accessing an invariant offset if possible.

This release includes a new jiff::fmt::friendly module for formatting and parsing durations in a more human readable format than what ISO 8601 specifies. ISO 8601 remains the "default" duration format in Jiff due to its widespread support. Here are some examples:

40d
40 days
1y1d
1yr 1d
3d4h59m
3 days, 4 hours, 59 minutes
3d 4h 59m
2h30m
2h 30m
1mo
1w
1 week
1w4d
1 wk 4 days
1m
0.0021s
0s
0d
0 days
3 mins 34s 123ms
3 mins 34.123 secs
3 mins 34,123s
1y1mo1d1h1m1.1s
1yr 1mo 1day 1hr 1min 1.1sec
1 year, 1 month, 1 day, 1 hour, 1 minute 1.1 seconds
1 year, 1 month, 1 day, 01:01:01.1

To quickly demonstrate this new feature, here's a simple CLI program using Clap:

use clap::Parser;
use jiff::{Span, Zoned};

#[derive(Parser, Debug)]
#[command(version, about, long_about = None)]
struct Args {
    duration: Span,
}

fn main() {
    let args = Args::parse();
    println!("adding duration to now: {}", &Zoned::now() + args.duration);
}

And running the program:

$ cargo run -q -- '1 year, 2 months, 5 hours'
adding duration to now: 2026-02-26T18:58:22-05:00[America/New_York]
$ cargo run -q -- 'P1Y2MT5H'  # ISO 8601 durations are supported too!
adding duration to now: 2026-02-26T19:00:57-05:00[America/New_York]

With Jiff, you should no longer need to pull in crates like humantime and humantime-serde to accomplish a similar task.

While this new format doesn't support any kind of internationalization, the prevalence of the humantime crate suggests there's a desire for something like this. The "friendly" format is meant to service all the same use cases as humantime does for durations, but in a way that doesn't let you shoot yourself in the foot.

The new "friendly" format is now the default for the Debug implementations of both Span and SignedDuration. It's also available via the "alternate" Display implementations for Span and SignedDuration as well. Moreover, the FromStr trait implementations for both Span and SignedDuration will parse both the ISO 8601 duration and this new "friendly" format. Finally, when serde integration is enabled, the Deserialize implementations for SignedDuration and Span also automatically parse either ISO 8601 or the friendly format. For serialization, ISO 8601 remains the default, but the jiff::fmt::serde module provides easy to use helpers to switch to the friendly format.

The jiff::fmt::friendly module documentation provides many more details, including a complete grammar for the format.

Enhancements:

• #143: Add Hash implementation for Zoned and Timestamp.

Bug fixes:

• #60: Use a better Debug output format for SignedDuration and Span.
• #111: Add a new "friendly" duration format.
• #138: Fix deserialization in serde_yml and serde_yaml crates.
• #161: Fix serde dependency configuration so that it builds in no-std mode.

This release fixes a bug where Jiff would sometimes fail to parse TZif files (found, typically, in /usr/share/zoneinfo on Unix systems). This occurred when the TZif file contained a time zone transition outside the range of Jiff's Timestamp type (which is -9999-01-01 to 9999-12-31). The bug fix works by clamping the out-of-range transitions to Jiff's supported range.

This bug only seems to occur in some environments where their TZif files contain more extreme values than what is typically found.

Bug fixes:

• #163: Fix a bug where Jiff would fail to parse some TZif files.

This release introduces new APIs to the RFC 2822 printer that explicitly print timestamps in a format strictly compatible with [RFC 9110].

Enhancements:

• #151: Add rfc2822::DateTimePrinter::timestamp_to_rfc9110_string method.

This release introduces a new jiff::tz::TimeZone::try_system API. It is like TimeZone::system, but returns an error instead of an automatic fall back to UTC when the system time zone could not be discovered.

This also includes an update to the bundled [IANA Time Zone Database] to the 2024b release in the jiff-tzdb crate. As a reminder, the bundled database is not used or included on Unix platforms by default. See [PLATFORM] for more details.

Enhancements:

• #65: Add TimeZone::try_system for fallibly determining the system's time zone.
• #125: Update to the 2024b release of the [IANA Time Zone Database].

This release introduces some new minor APIs that support formatting Timestamp values as RFC 3339 strings with a specific offset.

Previously, using the standard formatting routines that Jiff provides, it was only possible to format a Timestamp using Zulu time. For example:

use jiff::Timestamp;

assert_eq!(
    Timestamp::UNIX_EPOCH.to_string(),
    "1970-01-01T00:00:00Z",
);

This is fine most use cases, but it can be useful on occasion to format a Timestamp with a specific offset. While this isn't as expressive as formatting a datetime with a time zone (e.g., with an IANA time zone identifier), it may be useful in contexts where you just want to "hint" at what a user's local time is. To that end, there is a new Timestamp::display_with_offset method that makes this possible:

use jiff::{tz, Timestamp};

assert_eq!(
    Timestamp::UNIX_EPOCH.display_with_offset(tz::offset(-5)).to_string(),
    "1969-12-31T19:00:00-05:00",
);

A corresponding API was added to jiff::fmt::temporal::DateTimePrinter for lower level use.

Moreover, this release also includes new convenience APIs on the Temporal and RFC 2822 printer types for returning strings. For example, previously, if you were using the RFC 2822 printer to format a Timestamp, you had to do this:

use jiff::{fmt::rfc2822::DateTimePrinter, Timestamp};

let mut buf = String::new();
DateTimePrinter::new().print_timestamp(&Timestamp::UNIX_EPOCH, &mut buf).unwrap();
assert_eq!(buf, "Thu, 1 Jan 1970 00:00:00 -0000");

But now you can just do this:

use jiff::{fmt::rfc2822::DateTimePrinter, Timestamp};

assert_eq!(
    DateTimePrinter::new().timestamp_to_string(&Timestamp::UNIX_EPOCH).unwrap(),
    "Thu, 1 Jan 1970 00:00:00 -0000",
);

Enhancements:

• #122: Support formatting Timestamp to an RFC 3339 string with a specific offset.

This release includes a few small enhancements that have been requested over the last several weeks. The biggest enhancement is a new jiff::fmt::serde sub-module. It provides convenience routines similar to Chrono's chrono::serde sub-module for serializing and deserializing between a jiff::Timestamp and an integer number of seconds, milliseconds, microseconds or nanoseconds. For example:

use jiff::Timestamp;

#[derive(serde::Serialize, serde::Deserialize)]
struct Record {
    #[serde(with = "jiff::fmt::serde::timestamp::second::required")]
    timestamp: Timestamp,
}

let json = r#"{"timestamp":1517644800}"#;
let got: Record = serde_json::from_str(&json).unwrap();
assert_eq!(got.timestamp, Timestamp::from_second(1517644800).unwrap());
assert_eq!(serde_json::to_string(&got).unwrap(), json);

If you need to support optional timestamps via Option<Timestamp>, then use jiff::fmt::serde::timestamp::second::optional instead. Similarly, if you need to support milliseconds instead of seconds, then replace second with millisecond in the module path.

Enhancements:

• #78: Add BrokenDownTime::set_{offset,iana_time_zone} APIs.
• #93: Add note about using Timestamp::now().to_zoned() instead of Zoned::now().with_time_zone().
• #101: Add new jiff::fmt::serde module for integration with integer timestamps.
• #117: Remove unsafe usage in libm functions (applicable only to no-std users).

This release features a small bug fix where Jiff will detect an IANA time zone identifier in some cases where it wouldn't before. While Jiff would previously read the symlink metadata on /etc/localtime by default to discover the system configured time zone on Unix systems, it wouldn't do so when TZ=/etc/localtime. There's really no reason not to, so this release of Jiff is fixed to use symlink sniffing on file paths provided by the TZ environment variable.

Bug fixes:

• #113: When TZ=/etc/localtime, use symlink metadata to detect IANA identifier.

This release introduces new options for controlling the precision of fractional seconds when printing Zoned, Timestamp, civil::DateTime or civil::Time values. This is principally exposed via jiff::fmt::temporal::DateTimePrinter::precision, but it's also available via the standard library's formatting machinery. For example, if zdt is a jiff::Zoned, then format!("{zdt:.6}") will format it into a string with microsecond precision, even if its fractional component is zero.

Enhancements:

• #92: Support setting the precision of fractional seconds when printing datetimes.