How to Generate UUID v4 Identifiers
UUID Generation
When to Generate UUIDs
Use UUID v4 when you need globally unique identifiers without a central coordinator — database primary keys, API correlation IDs, file names in distributed storage, or session tokens where collision risk must be negligible.
Real-World Examples
PostgreSQL row ID: 550e8400-e29b-41d4-a716-446655440000
API request trace ID attached to log lines across microservices
S3 object key prefix before upload to avoid filename collisions
Common Mistakes
- Using
Math.random()instead of cryptographically secure randomness for security-sensitive IDs - Assuming UUIDs are always sequential — v4 values are random and poor for B-tree index locality
- Storing UUIDs as strings without considering index size vs binary (16-byte) storage
Edge Cases
- Collision probability is astronomically low but not zero — birthday paradox applies at extreme scale
- Some databases prefer UUID v7 (time-ordered) for index performance — use the ULID tool for sortable IDs
- Uppercase vs lowercase UUID strings are equivalent — normalize for comparisons
Developer Tips
- Node.js:
crypto.randomUUID()in Node 16+ - PostgreSQL:
gen_random_uuid()with the pgcrypto extension - For sortable IDs, prefer ULIDs or UUID v7 over v4
Frequently asked questions
What UUID version does this generator create?
This tool generates UUID version 4 (random) using the browser crypto.randomUUID() API, which produces RFC 4122-compliant identifiers with 122 bits of randomness.
Can I generate multiple UUIDs at once?
Yes. Enter a number between 1 and 50 in the input field, or leave it empty to generate a single UUID.
Are generated UUIDs cryptographically secure?
Yes. The tool uses crypto.randomUUID(), which relies on the browser secure random number generator — suitable for production identifiers.