UUID Guide: What They Are and When to Use Them

Published February 4, 2026 • 10 min read

UUIDs (Universally Unique Identifiers) are 128-bit numbers used to uniquely identify information. If you've seen IDs like 550e8400-e29b-41d4-a716-446655440000, that's a UUID. This guide explains everything you need to know.

What is a UUID?

A UUID is a 36-character string (32 hex digits + 4 hyphens) that's practically guaranteed to be unique. The format looks like:

550e8400-e29b-41d4-a716-446655440000
├──────┤ ├──┤ ├──┤ ├──┤ ├──────────┤
   8      4    4    4        12

UUID vs GUID

GUID (Globally Unique Identifier) is Microsoft's term for UUID. They're the same thing. Use "UUID" for cross-platform code.

UUID Versions

Version 1 (Time-based)

• Generated from timestamp + MAC address
• Can leak machine info
• Sortable by time
• Use when: You need time-ordered IDs and control the infrastructure

Version 4 (Random)

• Generated from random/pseudo-random numbers
• Most common version
• No privacy concerns
• Use when: You need truly unique IDs (99.9% of cases)

Other Versions

Versions 2, 3, and 5 exist but are rarely used. Stick with v4 unless you have specific needs.

When to Use UUIDs

✅ Good Use Cases

• Distributed systems: Multiple servers generating IDs without coordination
• API keys: Unguessable identifiers
• Session tokens: Unique per session
• File uploads: Prevent name collisions
• Microservices: IDs generated across services
• Public URLs: Obscure sequential patterns

❌ When NOT to Use UUIDs

• Performance-critical databases: UUIDs are larger and slower to index than integers
• Human-readable IDs: Use short codes instead (e.g., "ORD-1234")
• URLs you want to remember: UUIDs are not memorable

UUID vs Auto-Increment IDs

How to Generate UUIDs

JavaScript/Node.js

// Native (Node 16+)
import { randomUUID } from 'crypto';
const uuid = randomUUID();

// Browser
const uuid = crypto.randomUUID();

Python

import uuid
new_uuid = uuid.uuid4()
print(str(new_uuid))

Go

import "github.com/google/uuid"
newUUID := uuid.New()
fmt.Println(newUUID.String())

PHP

$uuid = \Ramsey\Uuid\Uuid::uuid4();
echo $uuid->toString();

Java

import java.util.UUID;
UUID uuid = UUID.randomUUID();
System.out.println(uuid.toString());

SQL (PostgreSQL)

SELECT gen_random_uuid();

Are UUIDs Really Unique?

For practical purposes, yes. The collision probability for UUID v4 is:

1 in 5.3 × 10³⁶

You'd need to generate 1 billion UUIDs per second for 100 years to have a 50% chance of collision. It won't happen.

Common UUID Mistakes

1. Using UUIDs as Primary Keys in High-Write Tables

UUIDs fragment indexes. Use sequential IDs or consider UUIDv7 (time-ordered).

2. Storing UUIDs as Strings

Store as binary (16 bytes) instead of string (36 bytes). Saves space and improves performance.

3. Not Validating UUID Format

Always validate UUIDs from user input. Invalid formats can cause database errors.

Tools

Need to generate UUIDs quickly? Try our free UUID generator. Generate one or thousands at once, no signup required.

Conclusion

UUIDs are perfect for distributed systems, API keys, and anywhere you need globally unique identifiers without coordination. Use v4 for most cases, and consider performance trade-offs for high-scale databases.