Generating UUIDs in Rust

Updated April 26, 2026 · 5 min read · by Samuel Yoo

The uuid crate is the universal Rust UUID library — well-maintained, no-std friendly, with features gated behind flags so you only pay for what you use.

Setup

cargo add uuid --features v4,v7,serde

Each feature flag enables a specific version or capability:

Quick start

use uuid::Uuid;

fn main() {
    let v4 = Uuid::new_v4();
    let v7 = Uuid::now_v7();
    let v5 = Uuid::new_v5(&Uuid::NAMESPACE_URL, b"https://example.com");

    println!("{}", v4);              // canonical form
    println!("{}", v4.simple());     // no hyphens
    println!("{}", v4.braced());     // {with-braces}
    println!("{}", v4.urn());        // urn:uuid:...
}

Uuid is Copy — a 16-byte value you pass around freely without borrowing. The various format methods return temporary structs that implement Display, so they’re zero-allocation when used with format! / write!.

Parsing

let s = "0e6f1b8c-2c33-4f1f-9c0b-2a3d4e5f6a7b";
let id: Uuid = s.parse()?;          // canonical
let id = Uuid::parse_str(s)?;       // explicit

parse_str accepts canonical, no-hyphens, braced, and URN forms. Invalid input returns uuid::Error.

Serde / JSON

use uuid::Uuid;
use serde::{Serialize, Deserialize};

#[derive(Serialize, Deserialize)]
struct User {
    id: Uuid,
    email: String,
}

let u = User { id: Uuid::now_v7(), email: "alice@example.com".into() };
let json = serde_json::to_string(&u)?;
// {"id":"01928a47-3b30-7c5e-9d1a-f0b8c4a7e923","email":"alice@example.com"}

UUIDs serialize to their canonical string by default.

sqlx integration

[dependencies]
sqlx = { version = "0.8", features = ["runtime-tokio", "postgres", "uuid"] }
uuid = { version = "1", features = ["v7", "serde"] }

use sqlx::{PgPool, Row};
use uuid::Uuid;

#[derive(sqlx::FromRow)]
struct User {
    id: Uuid,
    email: String,
}

let user: User = sqlx::query_as(
    "SELECT id, email FROM users WHERE id = $1"
)
.bind(id)
.fetch_one(&pool)
.await?;

let id = Uuid::now_v7();
sqlx::query("INSERT INTO users (id, email) VALUES ($1, $2)")
    .bind(id)
    .bind(&email)
    .execute(&pool)
    .await?;

sqlx’s uuid feature enables transparent conversion between PostgreSQL uuid and Rust Uuid.

Diesel integration

[dependencies]
diesel = { version = "2.2", features = ["postgres", "uuid"] }
uuid = { version = "1", features = ["v7"] }

use diesel::prelude::*;
use uuid::Uuid;

#[derive(Insertable, Queryable, Selectable)]
#[diesel(table_name = users)]
struct User {
    id: Uuid,
    email: String,
}

Bytes and byte order

let id = Uuid::new_v4();
let bytes: &[u8; 16] = id.as_bytes();   // borrowed, RFC 4122 order
let owned: [u8; 16] = id.into_bytes();  // owned

let from_bytes = Uuid::from_bytes(owned);

This is RFC 4122 / network byte order. For Microsoft’s GUID byte order (when reading SQL Server uniqueidentifier raw bytes), see UUID vs GUID.

Const UUIDs (compile-time)

use uuid::uuid;

const ORDERS_NS: Uuid = uuid!("8a4c2d6e-1f3b-4a5c-9d8e-7f6a5b4c3d2e");

The uuid! macro parses at compile time, so an invalid literal becomes a compile error rather than a runtime panic.

WASM / browsers

uuid = { version = "1", features = ["v4", "v7", "js"] }

The js feature pulls in getrandom configured to use the browser’s crypto.getRandomValues(). Without it, you’ll get a runtime error in WASM.

no_std

uuid = { version = "1", default-features = false, features = ["v4"] }

Disable default features and pick what you need. The crate works on no_std for embedded use cases.

Performance

Default uses getrandom (cryptographically secure). fast-rng uses rand with a faster (non-secure) PRNG. Don’t use fast-rng for security tokens.

Common pitfalls

• Uuid::new_v4() requires the v4 feature flag. Forgetting to enable it in Cargo.toml produces a confusing “method not found” error. Same for v7 / v5 / etc.
• Don’t use fast-rng UUIDs as session tokens. They’re fast because they’re not cryptographic. Use the default RNG for any unguessable token.
• Uuid::default() is the nil UUID (all zeros). If a Uuid field has the default trait used for initialization, check before using it as a real ID.
• WASM targets need the js feature. Without it, random UUID generation panics with “no implementation for this target.”

Cheat sheet

Try the tools

• UUID generator — generate v4, v7, v1/v3/v5
• UUID v7 generator — modern primary keys
• UUID validator — decode and check version