UUID & ULID Generator

Free online UUID (v1–v7) and ULID generator with bulk generation, timestamp extraction, and RFC 9562 compliance

UUID v4: Random

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UUID v4

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Which one should I use?

Use Case	Best Choice	Why
Web APIs & General	UUID v4	Universal compatibility, fully random
Database Primary Keys	UUID v7 ULID	Timestamp-ordered, great B-tree perf
URLs & Short IDs	ULID	26 chars, URL-safe, sortable
Deterministic IDs	UUID v5	Same input = same output (SHA-1)
Event Ordering	UUID v7 ULID	Millisecond timestamp + random suffix

UUID Guide

Understanding UUID Versions

UUIDs come in several versions, each designed for specific use cases. UUID v1 combines a timestamp with the MAC address of the generating machine, making it unique but potentially exposing hardware information. UUID v3 and v5 are namespace-based, generating deterministic identifiers by hashing a namespace and name using MD5 or SHA-1 respectively.

UUID v4 remains the most widely used version, generating completely random identifiers with 122 bits of randomness. For modern applications, UUID v7 (introduced in RFC 9562) offers the best of both worlds: a Unix timestamp prefix for natural sorting combined with random bits for uniqueness. This makes v7 ideal for database primary keys where index performance matters.

UUID vs ULID: Which One to Choose?

While UUIDs are the industry standard, ULIDs (Universally Unique Lexicographically Sortable Identifiers) offer some advantages. ULIDs are case-insensitive, use a more compact encoding (26 characters vs 36 for UUIDs), and are naturally sortable by creation time.

Choose UUID v7 if you need maximum compatibility with existing systems and libraries. Choose ULID if you want shorter identifiers and your stack supports them. Both are excellent choices for distributed systems where coordination-free ID generation is required.

Best Practices for Using UUIDs in Databases

When using UUIDs as primary keys, consider these performance tips:

Use UUID v7 or ULID for better index locality due to their time-ordered nature
Store UUIDs as BINARY(16) instead of VARCHAR(36) to save storage space
Consider using UUID v4 for security-sensitive contexts where predictability must be avoided
In PostgreSQL, use the native UUID type for optimal performance

Frequently Asked Questions

What is a UUID?

A UUID (Universally Unique Identifier) is a 128-bit value used to uniquely identify information in computer systems. UUIDs are standardized by RFC 9562 and are designed to be unique across all devices and time.

What is a ULID and how does it differ from UUID?

A ULID (Universally Unique Lexicographically Sortable Identifier) is a 128-bit identifier that encodes a Unix timestamp in the first 48 bits, followed by 80 random bits. Unlike UUID v4, ULIDs are naturally sortable by creation time and use a compact 26-character Crockford Base32 encoding (vs 36 characters for UUID). They are ideal for database keys where sort order matters.

How many UUID v4s can I generate before a collision?

UUID v4 has 122 random bits, giving 5.3 × 10³⁶ possible values. By the birthday paradox, you would need to generate roughly 2.7 × 10¹⁸ UUIDs (2.7 quintillion) before there is a 50% chance of a single collision. For context, if you generated 1 billion UUIDs per second, it would take about 85 years to reach that threshold. In practice, UUID v4 collisions are not a concern for any real-world system.

Are UUIDs generated online secure?

Yes, when using this tool. All UUIDs and ULIDs are generated locally in your browser using cryptographically secure random number generators. Your data never leaves your device.

Why does UUID v4 cause B-tree index fragmentation?

UUID v4 values are fully random, so consecutive inserts scatter across the entire index instead of appending to the end. This forces the database to read and split random B-tree leaf pages, degrading write throughput and inflating index size by 20-40% compared to sequential keys. UUID v7 and ULID solve this by prefixing a millisecond timestamp, so new IDs naturally sort after previous ones. In PostgreSQL, switching from v4 to v7 can improve insert performance by 2-5x on large tables.

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Use Case

Best Choice

Web APIs & General

UUID v4

Database Primary Keys

UUID v7

ULID

URLs & Short IDs

ULID

Deterministic IDs

UUID v5

Event Ordering

UUID v7

ULID

UUID Guide

Understanding UUID Versions

UUID vs ULID: Which One to Choose?

Best Practices for Using UUIDs in Databases

When using UUIDs as primary keys, consider these performance tips:

Use UUID v7 or ULID for better index locality due to their time-ordered nature
Store UUIDs as BINARY(16) instead of VARCHAR(36) to save storage space
Consider using UUID v4 for security-sensitive contexts where predictability must be avoided
In PostgreSQL, use the native UUID type for optimal performance

Frequently Asked Questions

What is a UUID?

What is a ULID and how does it differ from UUID?

How many UUID v4s can I generate before a collision?

Are UUIDs generated online secure?

Yes, when using this tool. All UUIDs and ULIDs are generated locally in your browser using cryptographically secure random number generators. Your data never leaves your device.

Why does UUID v4 cause B-tree index fragmentation?

UUID & ULID Generator

Which one should I use?

UUID Guide

Understanding UUID Versions

UUID vs ULID: Which One to Choose?

Best Practices for Using UUIDs in Databases

Frequently Asked Questions

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JWT

Hash

Cron

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Which one should I use?

UUID Guide

Understanding UUID Versions

UUID vs ULID: Which One to Choose?

Best Practices for Using UUIDs in Databases

Frequently Asked Questions