UUID Generator
Generate version 4 UUIDs singly or in bulk
UUID Generator tool
UUID Generator: key facts
- What it does
- Generate version 4 UUIDs singly or in bulk
- Category
- Developer Tools
- Cost
- Free, with no account, sign-up, or install.
- Your data
- Runs entirely in your browser — the files and text you enter are never uploaded to a server.
- Last reviewed
- . Report an incorrect result.
Understanding the UUID Generator
Unique identifiers are the quiet backbone of modern software — primary keys, request IDs, file names that must never collide. The UUID Generator produces version 4 UUIDs, the random variety, as many as you need at once.
Developers grab them constantly: seeding a database with test records, generating a correlation ID to trace a request through logs, or creating a unique key for a new resource without round-tripping to a server. Because UUID v4 is built from random data, two generated values colliding is astronomically unlikely, which is exactly why it is the default choice for distributed systems.
Need one or need a hundred — set the count and generate them in a single batch, then copy them all or download them as a file.
Getting a result
- Set the "Count" field to how many UUIDs you need (1 to 100).
- Click Generate.
- Read the list of version 4 UUIDs.
- Use an individual copy button for a single value, "Copy All" to grab the whole list, or Download to save them as uuids.txt.
Version 4, and the source of randomness
A version 4 UUID is 128 bits, almost all of them random: six bits are fixed to identify the version and variant, leaving 122 random. It is rendered as 32 hexadecimal digits in five hyphen-separated groups, and the digit that always reads 4 marks the version.
The generator uses the browser's built-in cryptographically secure UUID function where it is available, which is the correct source. Where it is not, it falls back to constructing the value from the ordinary pseudorandom generator. That fallback is fine for identifiers whose only requirement is uniqueness, and it is not suitable for anything where a value must be unguessable.
Collision probability at 122 bits is negligible for practical purposes — generating a billion per second for a century leaves the chance vanishingly small — which is what makes version 4 safe to generate independently on many machines without coordination.
- The version digit is always 4 and the variant digit is one of 8, 9, a, or b.
- The canonical form is 36 characters including four hyphens.
- Uniqueness holds across machines without any central allocator, which is the whole point.
Reasons to use it here
- It uses the browser's built-in crypto.randomUUID where available, so the values come from a cryptographically strong random source rather than a weak pseudo-random one, with a safe fallback for older browsers.
- You can generate up to 100 at once and export them with Copy All or as a downloadable text file — useful for seeding data in bulk.
- Generation is instant and local; no value is requested from or recorded by any server.
- It is free with no sign-up, so it fits straight into a scripting or testing workflow.
Choosing between versions, and the database cost
Version 4 is random. Version 1 embeds a timestamp and a node identifier, which makes it sortable but leaks the generating machine's MAC address and the creation time. Version 7, standardised more recently, is the pragmatic middle ground: a timestamp prefix followed by random bits, giving time-ordered values without the disclosure.
That ordering matters more than it sounds for storage. Random identifiers scatter inserts across a B-tree index, fragmenting pages and hurting write throughput and cache locality — a well-documented problem in databases that cluster on the primary key. Version 7 or a similar time-prefixed scheme keeps inserts largely sequential and avoids most of it.
Two further notes. A UUID is not a security token: version 4 values are unguessable if generated from a secure source, but treating an identifier as an authorisation mechanism means anyone who learns it gains access. And at 36 characters as text against 16 bytes as binary, storing UUIDs as strings more than doubles the space and slows comparison, so a native UUID column is worth using where the database offers one.
Frequently Asked Questions
What is a version 4 UUID?
A version 4 UUID is a 128-bit identifier generated mostly from random numbers, written as 32 hexadecimal digits in five hyphen-separated groups. The "4" appears in a fixed position to mark the version. It is the most common UUID type because it needs no central coordination to stay unique.
Are these UUIDs guaranteed to be unique?
Not literally guaranteed, but the probability of a collision is so vanishingly small that it is treated as unique for practical purposes. With 122 random bits, you would need to generate billions of UUIDs before a collision became remotely likely.
Are the generated UUIDs random and private?
Yes. They are generated in your browser using a cryptographically secure random source where available, and no value is sent to or stored on any server, so the UUIDs you create are yours alone.
Can I generate other UUID versions like v1 or v7?
This tool generates version 4 (random) UUIDs, which suit the large majority of use cases. Time-ordered versions like v1 or v7 are not produced here; if you specifically need sortable, timestamp-based identifiers, use a library that supports those versions.
