The ID That Doesn’t Need a Database Sequence
Auto-incrementing integers are great until you’ve got three microservices and a mobile app all trying to create records simultaneously. Who gets ID 42? With UUIDs, nobody has to ask. Each service generates its own identifiers independently, and the probability of a collision is about 1 in 5.3 x 10^36. You’d need to generate a billion UUIDs per second for 85 years to even reach a 50% chance of one duplicate.
UUID v4 uses 122 bits of cryptographic randomness to produce identifiers like f47ac10b-58cc-4372-a567-0e02b2c3d479. The 4 in the third group tells you it’s version 4 (random-based). The format is standardized in RFC 4122, and virtually every programming language, database, and framework speaks UUID natively.
This tool generates them using crypto.randomUUID(), supports bulk generation up to 100, and offers multiple formatting options. It also validates existing UUIDs. Need sortable IDs instead? Flip the version selector to v7 and you’ll get time-ordered identifiers that play nicely with database indexes.
Why UUIDs Over Sequential IDs
No coordination needed. In a distributed system, sequential IDs require a central authority (like a database sequence) to avoid conflicts. UUIDs don’t. Your frontend, backend, and mobile app can all generate IDs without talking to each other.
No enumeration attacks. With /users/42, an attacker can try /users/43, /users/44, and crawl your entire user base. With /users/f47ac10b-58cc-4372-a567-0e02b2c3d479, good luck guessing the next one.
Offline generation. Mobile apps and PWAs that work offline can create records with UUIDs and sync them later without ID conflicts.
Merge-friendly. Two databases with sequential IDs will collide when merged. Two databases with UUIDs won’t.
Format Options
Different systems expect different UUID formats:
- Standard:
550e8400-e29b-41d4-a716-446655440000(most common) - No hyphens:
550e8400e29b41d4a716446655440000(some databases prefer this) - Uppercase:
550E8400-E29B-41D4-A716-446655440000(Windows and SQL Server convention) - With braces:
{550e8400-e29b-41d4-a716-446655440000}(Microsoft COM/GUID format)
PostgreSQL has a native uuid type. MySQL can store them as CHAR(36) or BINARY(16). MongoDB uses its own ObjectId format but accepts UUIDs too.
The Tradeoffs
UUIDs aren’t perfect. They’re 36 characters (or 16 bytes in binary), which is larger than a 4-byte integer. That means larger indexes, more storage, and slightly slower joins. For high-volume tables with billions of rows, that overhead adds up.
They’re also non-sequential, which hurts B-tree index performance because new UUIDs insert at random positions in the index rather than appending at the end. That’s exactly what UUID v7 fixes: it puts a 48-bit Unix-millisecond timestamp up front (followed by 74 bits of randomness and a monotonic counter), so freshly minted IDs sort in roughly creation order and append near the end of the index. The version digit becomes 7 instead of 4. Pick v7 here when you’re using these as primary keys; stick with v4 when you want pure randomness with no embedded time.
For bulk identifier needs, try the UUID Bulk Generator on Toolsvu (up to 1,000 at once). For custom-length random strings with prefixes (better suited for API keys), the Random Token Generator is more flexible. For shorter, URL-friendly IDs, check out the NanoID Generator.
Everything runs in your browser via crypto.randomUUID(). Works offline too.