What is a UUID?
A UUID (Universally Unique Identifier) is a 128-bit identifier that is, in practice, unique: independent systems can create them without coordinating and never expect a collision. UUID v4 is random, v7 (RFC 9562) starts with a timestamp so it sorts by creation time, and a ULID (Universally Unique Lexicographically Sortable Identifier) is a time-ordered 128-bit ID written in Base32. All generation happens in your browser using the Web Crypto API.
What a UUID is and why it is useful
A UUID (universally unique identifier) is a 128-bit value written as 32 hexadecimal digits in five groups, such as 550e8400-e29b-41d4-a716-446655440000. Its purpose is to let independent systems generate identifiers that will not collide, without asking a central database for the next number. That makes UUIDs ideal for primary keys, distributed systems, and offline clients that create records before syncing.
The chance of two randomly generated version-4 UUIDs colliding is so small it can be treated as zero in practice, which is why they are trusted to be unique across servers, databases, and time.
Versions: v4, v7, and ULID
Version 4 UUIDs are fully random and are the common default. Version 7 UUIDs embed a millisecond timestamp in their leading bits, so they sort in the order they were created — a real advantage for database indexes, where random v4 keys can hurt insert performance. ULIDs are a related, sortable, timestamp-based identifier written in a more compact 26-character alphabet.
This generator keeps v7 UUIDs and ULIDs in order even when many are created in the same millisecond: v7 uses the counter method from RFC 9562, and ULIDs increment their random part as the ULID specification describes. A bulk batch therefore sorts in exactly the order it was generated, and each v7 or ULID shows the time it encodes.
UUIDs versus auto-increment IDs
Sequential database IDs are compact but reveal how many records exist and require a central authority to hand out the next value. UUIDs trade a little size for the ability to generate an identifier anywhere — on a client, offline, or across many servers — with no coordination and no risk of collision.
How to generate a UUID
- 1Choose a type. Pick UUID v4 for random identifiers, UUID v7 for time-ordered ones, or ULID for time-ordered IDs in compact Base32. For UUIDs, choose uppercase or no dashes if you need them.
- 2Click Generate. Each click creates a new identifier. Bulk creates as many as the Bulk count (10 by default, up to 1,000), in creation order.
- 3Copy the result. Use Copy next to an ID, or Copy all for a batch, and paste it into your database, code, or configuration.
Examples
A version-4 UUID
Fully random.
Input
Generate (v4)
Output
3f2504e0-4f89-41d3-9a0c-0305e82c3301
A version-7 UUID
Time-ordered — its first 48 bits are the creation time, 2024-05-09 02:28:52.474 UTC.
Input
Generate (v7)
Output
018f5b2e-9c7a-7c3e-b1a2-4e5f6a7b8c9d
UUID format
The shape of a UUID string.
| Part | Detail |
|---|---|
| Length | 36 characters (32 hex digits + 4 hyphens) |
| Groups | 8-4-4-4-12 |
| Version digit | 1st digit of group 3 (4 for v4, 7 for v7) |
| Bits | 128 (6 fixed for version and variant) |
| Example | 550e8400-e29b-41d4-a716-446655440000 |
Frequently asked questions
Are these UUIDs really unique?
For practical purposes, yes. A version-4 UUID has 122 random bits, so the odds of a collision are astronomically small and safe to ignore in real systems.
What is the difference between v4 and v7?
v4 is fully random. v7 puts a millisecond timestamp in the high bits so the identifiers sort by creation time, which is friendlier to database indexes. This tool also keeps v7 UUIDs made in the same millisecond in order.
Should I use a UUID as a database primary key?
Yes, especially in distributed systems. If insert ordering matters for your index, prefer v7 or ULID over random v4.
What is a ULID?
A 128-bit identifier like a UUID — a 48-bit millisecond timestamp and 80 random bits — written as 26 Crockford Base32 characters. Because the timestamp comes first, ULIDs sort by creation time, and within one millisecond this tool increments the random part so they stay in order.
Are the UUIDs generated privately?
Yes. They are created in your browser and aren't sent to a server. The only exception is the Share link button, which uploads the IDs on screen and your settings when you click it, so the link can show them again.
Is it free?
Yes — free, with up to 1,000 IDs per click and no limit on clicks.
Are UUIDs safe to expose in URLs?
A random v4 UUID reveals nothing about record counts or creation order, unlike a sequential integer ID, which leaks how many records exist. A v7 UUID or ULID does reveal when the record was created, to the millisecond, so use v4 where creation times should stay private.