About the UUID / ULID Generator
UUIDs (Universally Unique Identifiers) and ULIDs (Universally Unique Lexicographically sortable Identifiers) are both used to generate unique IDs without a central coordinating authority — common for database primary keys, request IDs, and distributed system identifiers.
This tool generates cryptographically random UUIDs (version 4) and time-ordered ULIDs in bulk, so you can quickly grab however many identifiers you need for testing or seeding data.
How it works
- Set how many identifiers you want using the count control.
- Click Generate under UUIDs for random v4 UUIDs, or under ULIDs for time-sortable identifiers.
- Copy the generated list directly into your test data, seed script, or code.
Common use cases
- Seeding test data: Generating a batch of UUIDs to use as primary keys when populating a test database with sample records.
- Choosing sortable IDs for a new table: Using ULIDs instead of UUIDs for a table where you want IDs that naturally sort by creation time, improving index locality.
- Generating a one-off request ID: Grabbing a single UUID to use as a correlation ID when manually testing an API request.
Frequently asked questions
What's the difference between a UUID and a ULID?
A version 4 UUID is 128 bits of pure randomness with no inherent ordering, while a ULID encodes a millisecond timestamp in its first 10 characters followed by 16 random characters — meaning ULIDs generated later always sort after earlier ones lexicographically, which UUIDs don't guarantee.
Are these UUIDs cryptographically random?
Yes — they're generated using the browser's `crypto.getRandomValues()` API, a cryptographically secure random number source, not a weaker `Math.random()`-based generator.
Can two generated UUIDs ever collide?
In practice, no — a version 4 UUID has 122 random bits, giving such an astronomically large number of possible values that accidental collisions are considered practically impossible even at massive scale.
Why would I choose ULID over UUID for a database primary key?
Because ULIDs are naturally time-ordered, inserting them into a database index causes far less fragmentation than randomly-ordered UUIDs, which can meaningfully improve write performance and index locality on large tables.
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