UUID v6 Guide

Skip straight to the UUID v6 generator or keep reading to understand time-ordered UUID generation.

UUID v6 is a modern time-ordered UUID that keeps the timestamp at the front of the identifier without exposing a MAC address. This guide explains how UUID v6 differs from other versions and shows how to use it with popular languages and databases.

What is UUID v6?

UUID Version 6 is a reordered UUID v1 with a timestamp prefix. Instead of the original UUID v1 layout, UUID v6 places the 60-bit timestamp first so UUID values sort naturally when treated as strings. It is defined in RFC 9562 as a backward-compatible way to preserve v1 semantics while improving sortability.

8ace1c11-5b22-6dd1-95b4-682cc3acb675
└───────┘ └──┘ └───┘ └───────────────┘
 timestamp  ver  clock  node
 (60-bit)   6    seq   (48-bit)

Why choose UUID v6?

Time-ordered sorting

UUID v6 orders its timestamp bits at the front of the identifier. That means a simple lexical sort produces creation order, which is ideal for databases and log streams.

Better than UUID v1 for indexing

UUID v1 embeds a timestamp but leaves the low-order time and node fields first, which causes poor index locality. UUID v6 fixes that by moving the timestamp to the top while still preserving the original v1 timestamp and node information.

How it compares to UUID v7

UUID v7 is the newer recommendation for time-ordered UUIDs because it uses a millisecond Unix timestamp and fully random payload bits. UUID v6 can still be useful when you want a more direct upgrade path from v1 or when compatibility with libraries and systems that already understand version 6 is required.

When to use UUID v4 instead

Use UUID v4 when you do not want any timestamp semantics embedded in the value. UUID v6 is best when chronological ordering and index locality are important.

UUID v6 structure

• timestamp: 60 bits from the original UUID v1 time layout.
• version: the version nibble is 6.
• clock sequence: 14 bits used to preserve uniqueness when the clock moves backwards.
• node: 48 bits of node information or random data, matching UUID v1 style.

Code examples for UUID v6

# Install
npm install uuid

import { v6 as uuidv6 } from 'uuid';

const id = uuidv6();
console.log(id);

function formatHex(bytes) {
  return [...bytes].map(b => b.toString(16).padStart(2, '0')).join('');
}

function uuidv6() {
  const ts = BigInt(Date.now()) * 10000n + 0x01b21dd213814000n;
  const bytes = new Uint8Array(16);
  const rnd = new Uint8Array(8);
  crypto.getRandomValues(rnd);

  // timestamp high 48 bits
  for (let i = 0; i < 6; i++) {
    bytes[i] = Number((ts >> BigInt(40 - 8 * i)) & 0xffn);
  }
  bytes[6] = 0x60 | ((Number((ts >> 24n) & 0xffn) ) & 0x0f);
  bytes[7] = Number((ts >> 16n) & 0xffn);
  bytes[8] = 0x80 | (rnd[0] & 0x3f);
  bytes.set(rnd.subarray(1), 9);

  const h = formatHex(bytes);
  return `${h.slice(0,8)}-${h.slice(8,12)}-${h.slice(12,16)}-${h.slice(16,20)}-${h.slice(20)}`;
}

console.log(uuidv6());

# Install
pip install uuid6

import uuid6

uid = uuid6.uuid6()
print(uid)
# version 6
print(uid.version)

import uuid6
from datetime import datetime, timezone

uid = uuid6.uuid6()
ms = (uid.int >> 80) - 0x01b21dd213814000
print(datetime.fromtimestamp(ms / 1000, tz=timezone.utc))

# Install
go get github.com/google/uuid

package main

import (
    "fmt"
    "github.com/google/uuid"
)

func main() {
    id, err := uuid.NewV6()
    if err != nil {
        panic(err)
    }
    fmt.Println(id)
}

<!-- Maven dependency -->
<dependency>
  <groupId>com.fasterxml.uuid</groupId>
  <artifactId>java-uuid-generator</artifactId>
  <version>5.1.0</version>
</dependency>

import com.fasterxml.uuid.Generators;
import java.util.UUID;

UUID id = Generators.timeBasedGenerator().generate();
System.out.println(id);

# Install
dotnet add package UUIDNext

using UUIDNext;

var id = Uuid.NewV6();
Console.WriteLine(id);
// → 8ace1c11-5b22-6dd1-95b4-682cc3acb675

# Install
composer require ramsey/uuid

use Ramsey\Uuid\Uuid;

$id = Uuid::uuid6()->toString();
echo $id;

# Install
gem install uuidtools

require 'uuidtools'

puts UUIDTools::UUID.uuid_v6

# Cargo.toml
[dependencies]
uuid = { version = "1", features = ["v6"] }

use uuid::Uuid;

fn main() {
    let id = Uuid::new_v6();
    println!("{}", id);
}

# mix.exs dependencies
{:uuid, "~> 2.0"}

UUID = Elixir.UUID

id = UUID.uuid6()
IO.puts(id)

% rebar.config
{deps, [{uuid, "*"}]}

UUID = uuid:uuid6().
io:format("~s~n", [UUID]).

CREATE TABLE events (
  id UUID PRIMARY KEY,
  name TEXT
);

-- Insert UUID v6 from your app
INSERT INTO events (id, name) VALUES ('8ace1c11-5b22-6dd1-95b4-682cc3acb675', 'signup');

CREATE TABLE events (
  id BINARY(16) PRIMARY KEY,
  title VARCHAR(200)
);

Frequently asked questions

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