What Is a UUID?
The UUID & ULID Generator creates universally unique identifiers for developers, database administrators and QA engineers. UUIDs are 128-bit values used as primary keys, correlation IDs and idempotency tokens because they can be generated independently without coordination and never collide in practice. This tool supports three formats: UUID v4 (fully random), UUID v7 (time-ordered, ideal for database indexes because it sorts chronologically) and ULID (a compact, URL-friendly, lexicographically sortable identifier). Everything is generated locally in your browser using the cryptographically secure Web Crypto API, so the values are safe to use and never leave your device.
A UUID (Universally Unique Identifier) is a 128-bit number formatted as 32 hexadecimal digits separated by hyphens — for example, 550e8400-e29b-41d4-a716-446655440000. Version 4 UUIDs, which this tool generates, are filled with random bits from a cryptographically secure source, making the chance of a collision so astronomically small that UUIDs are treated as unique in practice across all systems worldwide.
How to Use the UUID Generator
- Choose the identifier type — UUID v4, UUID v7 or ULID — using the buttons at the top.
- Set how many you need (from 1 to 1000) and toggle formatting options such as hyphens and uppercase.
- Click Generate, then copy any single value or use Copy all to grab the whole batch for your seeds or tests.
Use Cases
- Assigning a unique identifier to a database record, user account or session without needing a central counter.
- Generating transaction IDs, request trace IDs or correlation IDs in distributed systems.
- Creating idempotency keys for API calls that must not be processed twice.
- Naming files, cache keys or temporary resources with no risk of collision.
How UUIDs Are Generated
Version 4 UUIDs are generated with window.crypto.getRandomValues() — the browser's cryptographically secure random number generator (CSPRNG). The 128 bits are filled randomly, then two specific bit fields are set to identify the version (4) and variant (RFC 4122) of the UUID.
The probability of generating the same UUID twice is approximately 1 in 5.3 × 10³⁶ — for practical purposes, impossible. That is why UUIDs can safely be generated independently on millions of devices without coordination.
Benefits and Use Cases
- Perfect for seeding databases, creating test fixtures and generating correlation IDs for distributed systems and logs.
- UUID v7 and ULID are time-ordered, reducing index fragmentation compared to random v4 keys in high-write databases.
- Runs entirely client-side with a secure random source, so generated identifiers are never transmitted or stored anywhere.
Privacy
UUIDs are generated entirely in your browser using the Web Crypto API. Nothing is sent to our servers. Because the generation is local, it also works offline once the page has loaded.