What Is a UUID? Universal Unique Identifier Explained

You've seen strings like 550e8400-e29b-41d4-a716-446655440000 in code, databases, and URLs. That's a UUID. Here's what it is and why developers use it.

What Is a UUID?

A UUID (Universally Unique Identifier) is a 128-bit number used to identify information uniquely across space and time. The chance of generating a duplicate is so low it's considered impossible for practical purposes.

Format: xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx (32 hex digits + 4 hyphens)

UUID Versions

| Version | How It's Generated | Best For | |---------|-------------------|----------| | v1 | Timestamp + MAC address | Time-sortable IDs | | v4 | Random numbers | Most common — general purpose | | v7 | Timestamp + random | Sortable, newer standard |

Why Developers Use UUIDs

Instead of Auto-Increment IDs

-- Old way: predictable, reveals row count
id: 1, 2, 3, 4...

-- UUID way: unpredictable, no info leak
id: a3f2b1c4-... , 8e7d6f5a-...

Benefits

No central authority needed — generate anywhere, no collision
Can't guess the next one — unlike sequential IDs
Works across systems — merge databases without ID conflicts
URL-safe — no special characters that break URLs

Generate UUIDs for Free

Use our UUID Generator:

Set how many UUIDs you need (1–100)
Click Generate
Copy or download — all generated in your browser

UUID v4 Structure

550e8400-e29b-41d4-a716-446655440000
       │       │
       │       └─ Version nibble (4 = v4)
       └─ Variant bits (indicates UUID layout)

Related Tools

UUID Generator — generate UUIDs instantly
Base64 Encoder — encode UUIDs to Base64