UUID vs ULID vs NanoID: Which ID Generator Should You Use?

Unique identifiers are essential for databases, APIs, and distributed systems. But with so many formats available, which one should you choose? This guide compares the most popular options.

UUID v4 (Random)

Format: 550e8400-e29b-41d4-a716-446655440000

UUID v4 is the most widely used identifier format. It generates 128-bit random identifiers with an incredibly low collision probability.

Pros:

• Universally supported (every database and programming language)
• Well-understood and battle-tested
• 2.71 × 10^18 possible values

Cons:

• Not sortable (random order hurts database index performance)
• 36 characters with hyphens (verbose)

Generate one: UUID Generator

UUID v7 (Time-Ordered)

Format: 01932c40-c3e0-7000-8000-000000000001

UUID v7 embeds a Unix timestamp in the most significant bits, making identifiers naturally sortable by creation time.

Pros:

• Time-ordered (great for database indexes)
• Same 128-bit size as UUID v4
• Backward compatible with UUID infrastructure

Cons:

• Newer standard (less library support)
• Slightly predictable (contains timestamp)

Generate one: UUID v7 Generator

ULID (Universally Unique Lexicographically Sortable Identifier)

Format: 01ARZ3NDEKTSV4RRFFQ69G5FAV

ULID uses Crockford's Base32 encoding for a shorter, URL-safe representation that is still lexicographically sortable.

Pros:

• Sortable by creation time
• Shorter than UUID (26 characters vs 36)
• URL-safe and case-insensitive

Cons:

• Less widely supported than UUID
• Custom encoding (not standard hex)

Generate one: ULID Generator

NanoID

Format: V1StGXR8_Z5jdHi6B-myT

NanoID is a tiny, URL-safe unique ID generator that lets you customize the alphabet and length.

Pros:

• Extremely short (customizable length)
• URL-safe characters
• Customizable alphabet

Cons:

• Not sortable
• Higher collision risk at short lengths
• Less standardization

Generate one: NanoID Generator

Comparison Table

| Feature | UUID v4 | UUID v7 | ULID | NanoID | |---------|---------|---------|------|--------| | Length | 36 chars | 36 chars | 26 chars | 21 chars | | Sortable | No | Yes | Yes | No | | URL-safe | Mostly | Mostly | Yes | Yes | | Collision risk | Very low | Very low | Very low | Low-Medium |

When to Use What

• UUID v4: General-purpose IDs, legacy systems, maximum compatibility
• UUID v7: Database primary keys, time-series data, new projects
• ULID: When you need shorter sortable IDs
• NanoID: URL slugs, short links, when size matters most

Try all of these generators for free — no signup required:

• UUID Generator
• UUID v7 Generator
• ULID Generator
• NanoID Generator