# SCRU128: Sortable, Clock and Random number-based Unique identifier
[](https://crates.io/crates/scru128)
[](https://github.com/scru128/rust/blob/main/LICENSE)
SCRU128 ID is yet another attempt to supersede [UUID] for the users who need
decentralized, globally unique time-ordered identifiers. SCRU128 is inspired by
[ULID] and [KSUID] and has the following features:
- 128-bit unsigned integer type
- Sortable by generation time (as integer and as text)
- 25-digit case-insensitive textual representation (Base36)
- 48-bit millisecond Unix timestamp that ensures useful life until year 10889
- Up to 281 trillion time-ordered but unpredictable unique IDs per millisecond
- 80-bit three-layer randomness for global uniqueness
```rust
// generate a new identifier object
let x = scru128::new();
println!("{x}"); // e.g. "036Z951MHJIKZIK2GSL81GR7L"
println!("{}", x.to_u128()); // as a 128-bit unsigned integer
// generate a textual representation directly
println!("{}", scru128::new_string()); // e.g. "036Z951MHZX67T63MQ9XE6Q0J"
```
See [SCRU128 Specification] for details.
[uuid]: https://en.wikipedia.org/wiki/Universally_unique_identifier
[ulid]: https://github.com/ulid/spec
[ksuid]: https://github.com/segmentio/ksuid
[scru128 specification]: https://github.com/scru128/spec
## Crate features
Default features:
- `std` enables the primary `new()` and `new_string()` functions and configures
`Scru128Generator` with the system clock and default random number generator.
Without `std`, this crate provides limited functionality available under
`no_std` environments.
Optional features:
- `serde` enables serialization/deserialization via serde.
## License
Licensed under the Apache License, Version 2.0.
## See also
- [docs.rs/scru128](https://docs.rs/scru128)