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UUID v4: Why and How to Generate Unique IDs

PureTools Team· 8 min read
UUID v4: Why and How to Generate Unique IDs

UUID v4: The Definitive Guide

A UUID (Universally Unique Identifier) is a 128-bit number that looks like this: 550e8400-e29b-41d4-a716-446655440000. The "universally unique" part means you can generate one on any machine, at any time, without coordinating with anyone, and be virtually certain it's unique.

How Unique Is "Unique"?

UUID v4 uses 122 random bits (6 bits are fixed for version/variant). That's 2^122 = 5.3 × 10^36 possible values. To put this in perspective:

  • Generate 1 billion UUIDs per second
  • Do this for 100 years
  • You'd have a 50% chance of ONE collision

In practice, your system will fail for a thousand other reasons before UUID collision becomes a concern.

UUID Versions

VersionBased onUse case
v1Timestamp + MAC addressSortable, but leaks device info
v4RandomMost popular, no information leakage
v5SHA-1 hash of namespace + nameDeterministic — same input = same UUID
v7Timestamp + random (new)Sortable like v1, random like v4

v4 is the default choice. v7 is gaining traction for database primary keys because it's sortable (better B-tree performance than random v4).

Generating UUIDs

JavaScript (browser):

crypto.randomUUID();
// "3b241101-e2bb-4d7a-8613-e4cf2408e94e"

Node.js:

import { randomUUID } from 'crypto';
const id = randomUUID();

Python:

import uuid
str(uuid.uuid4())

PostgreSQL:

SELECT gen_random_uuid();
-- or as column default:
CREATE TABLE users (
  id UUID DEFAULT gen_random_uuid() PRIMARY KEY,
  name TEXT NOT NULL
);

UUID vs Auto-Increment

Auto-increment IDs (1, 2, 3...) are simple but have drawbacks in distributed systems:

  • Predictable: Competitors can enumerate your data (/users/1, /users/2...)
  • Centralized: Need a single source to assign IDs (bottleneck)
  • Merge conflicts: Two databases both have id=42 for different records

UUIDs solve all three. The tradeoff: they're larger (16 bytes vs 4-8 bytes) and not human-friendly.

UUIDs in URLs

/users/550e8400-e29b-41d4-a716-446655440000 is ugly. Options:

  • Nanoid: /users/V1StGXR8_Z5jdHi6B — shorter, URL-safe
  • Hashids: /users/abc123 — encode numeric IDs into short strings
  • ULID: /users/01ARZ3NDEKTSV4RRFFQ69G5FAV — sortable, Crockford base32

Generate now: UUID Generator — v4 UUIDs with one click.

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