A Luxon-style datetime library for Rust with full TC39 Temporal types, embedded IANA timezone data, and zero allocations in hot paths.

Install · API Reference · Benchmarks · Docs

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5-line demo

use fastemporal::{ZonedDateTime, Duration};

let dt = ZonedDateTime::now()
    .plus(Duration::days(7))
    .in_timezone("America/New_York").unwrap();

println!("{}", dt.to_iso());
// 2025-06-14T14:32:00.000-04:00[America/New_York]

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Benchmark table

Benchmark	fastemporal	Luxon (Node.js)	Speedup
now()	74.3 ns	681.3 ns	9×
from_iso (parse)	102.1 ns	3,823.0 ns	37×
plus(days:7)	94.9 ns	3,539.0 ns	37×
in_timezone()	191.6 ns	7,875.8 ns	41×
to_iso()	69.0 ns	510.9 ns	7×
format(yyyy-MM-dd)	100.2 ns	1,870.4 ns	19×
start_of('day')	72.7 ns	1,221.1 ns	17×
diff(days)	59.5 ns	12,831.2 ns	216×
1 M tight loop	87.5 ns/op	3,526.3 ns/op	40×

Measured on Linux x64, release build. Rust: cargo bench (criterion 0.4). JS: Luxon 3.x on Node.js v22.
Regenerate: bash scripts/run_benchmarks.sh && python scripts/gen_bench_table.py --luxon luxon_results.txt

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Passes every Luxon + date-fns + Temporal test

All tests live in tests/luxon.rs, tests/datefns.rs, and tests/temporal.rs — ported from the upstream JS test suites. See the CI workflow for proof.

test result: ok. 76 passed  ← lib unit tests
test result: ok. 70 passed  ← tests/luxon.rs   (ported from luxon-master)
test result: ok. 54 passed  ← tests/datefns.rs  (ported from date-fns)
test result: ok. 70 passed  ← tests/temporal.rs (TC39 Temporal spec)
test result: ok. 62 passed  ← cargo test --doc  (every public fn has a runnable example)
─────────────────────────────
                  332 total, 0 failed

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Feature flags

Feature	Description	Default
tz-embedded	Bundle IANA timezone data into the binary	✓
tz-system	Use the OS /usr/share/zoneinfo at runtime	—
wasm	wasm-bindgen JS/WASM bindings	—
serde	Serialize / Deserialize for all types	—

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Installation

[dependencies]
fastemporal = "0.1"

Or:

cargo add fastemporal

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API reference

ZonedDateTime — main workhorse

Method	Luxon equivalent
ZonedDateTime::now()	DateTime.now()
ZonedDateTime::from_iso(s)	DateTime.fromISO(s)
.to_iso() -> String	.toISO()
.plus(Duration) -> Self	.plus({days:7})
.minus(Duration) -> Self	.minus(…)
.in_timezone(tz) -> Result<Self>	.setZone(tz)
.start_of(unit) -> Result<Self>	.startOf("day")
.end_of(unit) -> Result<Self>	.endOf("month")
.diff(other, unit) -> Result<Duration>	.diff(other, "days")
.format(fmt) -> String	.toFormat(fmt)
.year() .month() .day() .hour() .minute() .second()	field accessors

Duration

// Single-unit constructors
Duration::days(7)
Duration::hours(3)
Duration::years(1)
Duration::months(6)
Duration::millis(500)

// Multi-field builder
Duration::builder()
    .years(1).months(2).days(3)
    .hours(4).minutes(30)
    .build()

// Getters use num_ prefix (avoids conflict with constructors)
d.num_days()         // i32
d.num_hours()        // i32
d.num_milliseconds() // i32

Temporal types

use fastemporal::{PlainDate, PlainTime, PlainDateTime};

let d  = PlainDate::new(2025, 6, 7).unwrap();
let t  = PlainTime::new(14, 32, 0, 0).unwrap();
let dt = PlainDateTime::new(2025, 6, 7, 14, 32, 0, 0).unwrap();

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Format tokens

Supports both strftime (%Y-%m-%d) and Luxon-style (yyyy-MM-dd) tokens in the same format string.

Token	Meaning	Example
yyyy / %Y	4-digit year	2025
MM / %m	Month (zero-padded)	06
dd / %d	Day (zero-padded)	07
HH / %H	Hour 24h	14
mm / %M	Minute	32
ss / %S	Second	00
SSS / %3f	Milliseconds	123
%f	Nanoseconds (9 digits)	123456789
MMMM / %B	Full month name	June
MMM / %b	Short month name	Jun
EEEE / %A	Full weekday	Saturday
EEE / %a	Short weekday	Sat
ZZ / %Z	UTC offset	-04:00

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Running the benchmarks

Linux / macOS:

bash scripts/run_benchmarks.sh

Windows (PowerShell):

pwsh -File scripts/run_benchmarks.ps1

Manual steps:

# 1. Rust (criterion)
cargo bench

# 2. Luxon (requires: npm install luxon)
node scripts/luxon_bench.js bench > luxon_results.txt

# 3. Generate table
python scripts/gen_bench_table.py --luxon luxon_results.txt

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Phase roadmap

Version	Status	Scope
v0.1	✅ shipped	Core types · ISO 8601 parser · IANA tz · strftime + Luxon tokens · 332 tests · criterion benchmarks
v0.2	🔜 planned	no_std · with() field mutation · round() · since/until · Interval type · from_plain_datetime · 40 date-fns fns · serde ISO strings · WASM JS bindings
v1.0	🔮 future	Full TC39 Temporal spec compliance · non-Gregorian calendars · locale-aware formatting

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☕ Support

If fastemporal is useful to you, consider buying me a coffee — it helps keep the project moving.

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License

Licensed under either of

• MIT License
• Apache License, Version 2.0

at your option.