UUID Generator

What is a UUID?

A UUID (Universally Unique Identifier) is a 128-bit identifier standardised as RFC 4122. It is represented as 32 hexadecimal characters in the format xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx — always 36 characters including the four hyphens.

UUIDs are designed to be generated independently by any system, at any time, without coordination — and still be unique across the entire world. This makes them ideal for distributed systems, databases, and APIs where a central ID-issuing authority is impractical.

UUID versions compared — v1, v4, v5, v7

There are multiple UUID versions, each generated differently. Here's when to use each:

This tool generates UUID v4 — the most widely supported version, used by default in PostgreSQL, MySQL, MongoDB, and all major languages.

Generate a UUID in code

Need UUIDs in your project rather than via the browser? Here are the one-liners for every common language:

// Browser and Node.js 19+ (no library needed)
const id = crypto.randomUUID();
// → "110e8400-e29b-41d4-a716-446655440000"

// Node.js (older versions)
const { v4: uuidv4 } = require('uuid');
const id = uuidv4();

import uuid

# UUID v4 with hyphens
id = str(uuid.uuid4())
# → "550e8400-e29b-41d4-a716-446655440000"

# UUID v4 without hyphens (32 hex chars)
id_clean = uuid.uuid4().hex

# macOS
uuidgen | tr '[:upper:]' '[:lower:]'

# Linux
cat /proc/sys/kernel/random/uuid

-- Enable extension once
CREATE EXTENSION IF NOT EXISTS "pgcrypto";

-- Generate UUID v4
SELECT gen_random_uuid();

-- Use as default primary key
CREATE TABLE users (
  id UUID PRIMARY KEY DEFAULT gen_random_uuid(),
  email TEXT NOT NULL
);

When should you use a UUID?

• Database primary keys — UUIDs let you generate IDs client-side before inserting, avoiding database round-trips in distributed systems.
• API resource identifiers — UUIDs in URLs (e.g. /users/550e8400-e29b-41d4-a716-446655440000) don't expose sequential information to attackers.
• Session and auth tokens — UUID v4's randomness makes tokens unpredictable and resistant to enumeration attacks.
• File and upload naming — rename uploaded files to UUIDs to prevent path traversal attacks and name collisions.
• Event and message IDs — in event-driven systems (Kafka, RabbitMQ), UUID message IDs enable idempotency checks.
• Testing and mock data — generate unique identifiers quickly for test fixtures, seeds, and mock APIs.

If sort order matters (e.g. for database index performance or event ordering), consider UUID v7 or ULID instead — both are time-sortable.