UUID vs ULID: What’s the Difference and Which One Should You Use?

Identifiers are everywhere — in databases, APIs, authentication systems, and just about any application that needs to uniquely reference something.
For years, UUIDv4 has been the default unique ID format for developers. But recently, ULIDs have gained a lot of traction as a modern alternative.

If you’ve wondered whether you should switch, this guide breaks down the differences with clear examples and practical recommendations.

What Is a UUID?

A UUID (Universally Unique Identifier) is a 128-bit value typically represented like this:

550e8400-e29b-41d4-a716-446655440000

UUIDv4 — the most common version — is entirely random.

Benefits of UUIDs

• Very high uniqueness (128 bits)
• Well-established and widely supported
• No need for a centralized generator

Downsides of UUIDs

• Not sortable (v4 has no time component)
• Very long (36 characters with hyphens)
• Not human-friendly
• Causes fragmentation in some databases because insertion order is random

UUIDs still work great — but the randomness can be a drawback in modern systems.

What Is a ULID?

A ULID (Universally Unique Lexicographically Sortable Identifier) is a newer format that looks like this:

01JH7X5T4P7Q5TFXDW2HYX7TFB

ULIDs combine:

• 48 bits of timestamp
• 80 bits of randomness
• Crockford Base32 encoding

This makes them:

• sortable
• compact
• case-insensitive
• URL-safe
• easier to visually parse

Developers like ULIDs because they solve real-world problems UUIDs never addressed.

UUID vs ULID: Side-by-Side Comparison

Why Developers Are Switching to ULIDs

Here are the most common reasons:

1. Sortable by default

ULIDs encode the timestamp first, so sorting them also sorts by creation time.

Useful for:

• append-only logs
• event streams
• ordered API resources
• time-series data

UUIDs offer no such ordering.

2. Much better for databases

Random insertion of UUIDv4 values causes fragmentation in indexes like B-Trees.

ULIDs insert sequentially, improving performance.

Databases love predictable ordering.

3. Shorter and easier to work with

ULIDs are 26 characters compared to UUID’s 36.

They avoid:

• confusing characters
• unnecessary hyphens
• case sensitivity issues

Great for URLs, tokens, and user-facing IDs.

4. Still extremely unique

ULIDs maintain 80 bits of randomness — far more than enough for modern systems.

When Should You Use UUIDs?

Stick to UUIDv4 when you need:

• compatibility with older systems
• standardized formats across platforms
• consistent encoding across languages

UUIDs are reliable, predictable, and supported everywhere.

When Should You Use ULIDs?

Choose ULIDs for:

• modern APIs
• distributed systems
• event sourcing
• high-performance database inserts
• anything requiring natural ordering
• developer ergonomics

ULIDs feel like a modern fix for UUID limitations.

Real Examples

UUIDv4

c0c39d60-b96d-4c52-bb5d-29e35f4d8421

ULID

01JH7X7W4H3S5JF9AJ0E7X7W5P

Sorting Example (ULIDs)

01JH7X5T4P7Q5TFXDW2HYX7TFB← oldest
01JH7X5T4P7Q5TFXDW2HYX7TFC
01JH7X5T4P7Q5TFXDW2HYX7TFD← newest

The order naturally follows creation time — very useful.

Should You Migrate From UUID to ULID?

If you’re starting a new project, ULIDs are almost always the better choice.

If you’re maintaining an existing system:

• Migrate only if ordering or performance issues matter
• Otherwise, UUIDs remain perfectly valid

Generate UUIDs & ULIDs in Your Browser

Our free tool lets you generate UUIDs, ULIDs, or multiple IDs at once — all locally in your browser, using secure randomness from window.crypto.

Try it here: UUID & ULID Generator

No accounts. No tracking. No data sent to any server.

Final Thoughts

UUIDs aren’t going anywhere — they’re a proven standard and still useful.
But ULIDs offer real advantages for modern systems, including ordering, readability, and better performance.

If you want:

• safer identifiers
• easier debugging
• better database behavior
• time-sortable IDs

…ULIDs are an upgrade worth considering.